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WLU
AS101
FINAL EXAM
STUDY GUIDE
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MODULE 1 NOTES
-1 Astronomical Unit (AU) = 1.5 x 108km = 150M km

Average distance from Sun to the Earth
-Light-year (ly) = the distance light travels in one year, approx. 63,000 AU
-~ 13.7B years since the Big Bang
-The Moon’s distance from Earth = ~30x the Earth’s diameter = 384,000km
-The precession of the Earth’s rotational axis points to the North Star but this will change over time
- The Earth rotates from west to east in front of the Sun, giving both day and night
- the Sun rises in the east and sets in the west
- What you see in the sky depends on where you are

Canadians see constellations and stars that Australians never see
- Astronomers measure distances across the sky as angles in
units of degrees, arc minutes and arc seconds
Zenith – point in the sky directly overhead
Nadir – point directly below your feet
Celestial Equator – an extension of the Earth’s equator onto the
celestial sphere
Meridian – the line going from due north, through your zenith
and finishing due south
Arc Minutes – angular degrees are subdivided into arc minutes
(60’ in one degree)

Further divided into 60 arc seconds
Circumpolar Stars – stars that trace out complete circles
-The Earth moves along the ecliptic path its rotational axis, on which it makes one revolution each day, is
tipped to the ecliptic plane at a constant angle of 23.5° resulting in seasons on Earth
Tropic of Cancer – circle of latitude on the Earth that marks the most northerly position at which the Sun
may appear directly overhead at its zenith

Occurs once per year at the time of June Solstice
Tropic of Capricorn – southern hemisphere counterpart, marking the most southerly position at which
the Sun may appear directly overhead
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-The moon takes about a month to circle the Earth

As it circles the Earth it goes through phases of reflected sunlight
Orbital Period – from one full moon to the next – approximately 29.5 days
Sidereal Period – the time for one revolution relatives to the stars – approximately 27 days
Solar Eclipse – Moon blocks out the sunlight at high noon for a period of time
Lunar Eclipse – Earth blocks out the Sun’s light at midnight for a period of time
-Nodes: Points when the moon crosses through ecliptic plane – that’s when an eclipse is possible


Sun, Earth, and Moon must be lined up for an eclipse to be possible
Phase of moon must be new or full
Lunar Eclipse Types – Earth is between the Sun and Moon
a) Penumbral - most common, Moon passes through only the penumbra (sunlight is only partially
blocked). Result is that the Moon darkens only slightly.
b) Partial - part of Moon passes through the umbra while the rest passes through the penumbra. Result is
the part of the Moon is darkened completely but rest only slightly darkened with no clear demarcation
between the areas
c) Total - Moon passes entirely through the umbra. Result is that the Moon is completely dark during the
eclipse
Solar Eclipse Types – Moon is between the Earth and the Sun
a) Total – Moon is relatively close to the Earth in its orbit and the Moon’s umbra touches a small area of
the Earth’s surface; anyone within this area sees the sun totally blocked out
b) Partial – surrounding the small area of totality lies a larger area falling inside the Moon’s penumbral
shadow; anyone within this area sees the moon partially blocked out
c) Annular – Moon is relatively far from Earth and the Moon’s umbra may not reach the Earth surface at
all; anyone within the small area behind the umbra will see all of the Sun blocked out except a ring of
sunlight surrounding the Moon’s disk
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Five planets closest to the Earth are visible to the naked eye:
a) Mercury – at sunrise/sunset
b) Venus – closer to the horizon and bright
c) Mars – reddish colour
d) Jupiter – at night and comparatively bright
e) Saturn – slightly more difficult to spot
-2002: all five planets were lined up in the Western sky

Will occur again in 2040
-Planets generally follow motions of Sun and Moon  move eastward relative to stars

Occasionally, all planets appear to change direction and move westward relative to stars 
retrograde motion
o Inner planets move faster in orbit and catch up to outer, slower-moving planets, so the
outer planets appear to move backwards
-Stellar Parallax – occurs when we look at a nearby star from two vantage points


First when the Earth is at one extreme of its orbit around the Sun
Second when the Earth is at the opposite extreme six months later
- the nearby star appears to shift laterally against the background of stars behind it
-Stellar parallax allows us to measure distances to nearby stars AND also provides direct evidence that
the Earth really does revolved around the Sun
Declination – latitude, expressed in degrees, arcminutes/arcseconds north (+) or south (-) of the celestial
equator
Right Ascension – longitude; expressed in hours (h), minutes (m), and seconds (s) of time, from 0 to 24h
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Module 2 Lecture
Kepler published his three laws of planetary motion in the early 1600s:
a) Kepler’s First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus

All planets move around Sun in elliptical orbits with Sun as focus
Eccentricity was established whereby a circle has an eccentricity of zero and a straight line has an
eccentricity of 1; this is useful in determining the ellipses of orbits
b) Kepler’s Second Law: As a planet moves around in its orbit, it sweeps out equal areas in equal times

Radius vector joining any planet to Sun takes out equal areas in equal lengths of time
-When a planet is closer to the Sun (around its perihelion) it moves faster along its orbit than when close
to the aphelion (further point from the Sun)
-The planet moves from A to B (perihelion) in the same time that it takes to go from A’ to B’ (perihelion).
c) Kepler’s Third Law: The squares of the periods of any two planets have the same ratio as the cubes
of their semi-major axes
p2 = a 3
where p is the orbital period in years, and a is the avg. distance from the Sun in AU
Galileo introduced the telescope to the world in the early 1600s and proved the Earth was not the centre
of the universe and in fact the Sun-centred model was correct.
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Newton’s Universal Law of Gravitation: if the mass of either object is doubled, the force doubles
- also, if the distance between the masses doubles, the force diminishes by a factor of 4 (two squared)


Particle attract every other particles in universe using force directly proportional to product of
masses
Inversely proportional to square of distance between them
-Tides are a good example of this

Caused by the difference in gravitational attraction from one side of the Earth to the other
-When the Sun, Moon and Earth are all lined up, the tides are highest and called spring tides.
-During first and third quarter Moons, the tides are called neap tides
The Scientific Method
a) Deductive reasoning – process of concluding that something is true because it is a special case of a
general principle that is known to be true
- logically valid and this is the fundamental method in which mathematical facts are shown to be true
b) Inductive reasoning – process of reasoning that a general principle is true because the special cases
you’ve seen are true; for example, if all the people you’ve met from a particular town have been
intelligent, you might say that “all the residents of this town are smart”
Any model, hypothesis or theory can never be “proved” – a theory always remains a theory until some
observation discredits it.
Pseudoscience – false science; ex. making predictions based on tarot cards, psychic determinations
Nonscience – predictions based on intuition, faith, political conviction and tradition
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Cosmological Principal
- there is nothing special or unique about Earth; our location in the Universe is by chance
- the laws of physics and chemistry are valid throughout the universe
Orbital Motion
1. An object orbiting Earth, and any orbiting object, is actually falling (being accelerated due to the
gravitational force) toward Earth’s center
2. Objects orbiting each other actually revolve around their mutual center of mass
3. If you want to leave Earth and never return, you must give your spaceship a high enough velocity so it
will follow an open orbit
Momentum – the inertia an object has
p=mv

where p is momentum, m is mass and v is velocity
Properties of a Wave
- wavelength – the length of one wave (λ)
- frequency – the number of waves passing a point in space per second (f)
- speed – how fast the wave moves through space (c)
Speed = Frequency x wavelength
Every time light interacts with an object, at least one of the following occurs:
- absorption, transmission, or reflection
Doppler Effect – If a sound source is moving toward an observer, the waves in front of the sound source
get bunched up (closer together) so that the observer hears more waves per second than if the sound
source was not moving

If the sound source is moving away from the observer the waves behind the sound source get
pulled apart so that the observer hears fewer waves per second than if the sound source was not
moving
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-Light is a wave phenomenon and so the same effect is observed for light

Light coming from a moving object will have its frequency shifted to a higher or lower value
depending on the motion of the source

If we are looking at light from a star and we see the traditional hydrogen spectral line pattern (say
the Lyman series) but it is shifted towards the red end of the visible spectrum then we know that
the star is moving away from us
By measuring the amount the spectrum is shifted, we can determine the radial velocity of the star
If the spectrum is "blue-shifted" then the star is moving toward us.


Heat is transferred from one body to another body by three unique mechanisms:
- conduction – when the atoms in one part of the substance vibrate faster than at another part of the
substance (lower temperature) causing energy to be transferred
- convection – liquids and gas distribute heat with an actual transfer of mass
- radiation – makes use of a form of energy to remove/transport heat from one place to another
Conduction — heat flows from the hot solid
core to the inner mantle (red part) and from the top of
the mantle into the lithosphere (the outside crust)

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

Convection — as described above conduction cells form in the mantle
Radiation — at the surface of the planet energy is radiated into space in the form of light of
various frequencies
Types of Electromagnetic Radiation and their Sources
Type of Radiation
Wavelength Range (nm)
Object Temperature
Typical Sources
Less than 0.01
More than 108 K
Nuclear reactions
X-rays
0.01 - 20
106 - 108 K
Supernova remnants and solar corona
Ultraviolet
20 - 400
104 - 106 K
Very hot stars
Visible
400 - 700
103 - 104 K
Stars
Infrared
1000 - 1,000,000
10 - 103 K
Cool clouds of dust, planets, satellites
More than 1,000,000
Less than 10 K
No astronomical objects are this cold
Gamma Rays
Radio
Types of Telescopes
a) Refractive – similar to human eye, takes light in through a lens (A)
b) Reflective – more common, use one optical surface to collect light, a spherical mirror surface, which
focuses the light at a point in front of the mirror (B)
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Gravity
The universal law of gravitation:
1. Every mass attracts every other mass.
2. Attraction is directly proportional to the product of their masses. (The more
massive, the more attractive).
3. Attraction is inversely proportional to the square of the distance between their
centers (Ex: increase distance by 3, decrease force by 9).
Fg=G m1m2
d2
Ne ton’s Theory of Gra ity:



According to the law of gravitation, force of gravity between the Earth and an
object of mass m
o F=Gm mearth
d2
According to Newton’s second law, this force can also be written as
o F=ma
Equating the two, we see that the acceleration does not depend on the objects
mass
o g= Gmearth
d2
Mass vs. Weight:

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In physics mass and weight are related but are NOT the same thing.
Mass is the amount of matter in an object
Mass in an intrinsic property of an object
Mass is the same no matter what forces are acting on an object
Weight is the force of gravity exerted on an object
Weight is directly proportional to the mass
Example: doubling your mass doubles your weight
Weight varies from planet to planet since the acceleration due to gravity varies
Tides: Gravity in Action:

Tides are caused by small differences in gravitational forces
o As the earth and moon orbit around each other, they attract each other
gravitationally
o Because the side of the earth towards the moon is closer, the moon pulls
on it more strongly, and that pulls up a bulge
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o The moon pulls on earth more than it pulls on earth’s far side and that
produces a bulge on the far side
o Because there are two bulges, there are two high tides every day
Orbital Motion:

An object orbiting Earth is actually falling (being accelerated) towards earth’s
center
o An object in a stable orbit continuously misses the earth because of its
orbital velocity
Apparent Weight:



There is gravity in space
Weightlessness is due to a constant state of free-fall around the earth
The apparent weight of an object in free-fall is zero (no sensation of weight)
Escape Velocity:



If an object gains enough orbital energy, it may escape – change from a bound to
an unbound orbit
Escape velocity from earth = about 11km/s
Escape and orbital velocities don’t depend on the mass of an object
Kepler’s La s Re isited:


Kepler’s First Law: the orbit of earth planet around the Sun is an ellipse with the
Sun at one focus
o Newton showed that the inverse square law results in elliptical orbits for
the planets
o According to Newton’s first law of motion the planets will remain in their
orbits unless acted on by another force
As a planet moves around it’s orbit, it sweeps out equal areas in equal times
o The inverse square law means that when planets are closer to the sun they
feel a larger force and thus move faster
o If distance increases, velocity decreases, and vice versa, to keep angular
momentum constant
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Module 3 Notes
Comparative Planetology – seeking to understand the similarities and the differences between and
among the planets
Solar Nebular Theory – main theory of formation of our solar system

Imagines that some cataclysmic event initiated the collapse of a nebula that caused material
falling inward to some centre converting gravitational potential energy into kinetic energy making
the centre, or core, hotter and hotter
Terrestrial Planets – four inner planets - Mercury, Venus, Earth and Mars

Small, dense, rocky worlds with little or no atmosphere
Jovian Planets – four outer planets – Jupiter, Saturn, Uranus, and Neptune

Large, low-density worlds with thick atmospheres and liquid or ice interiors
Planetary Characteristics:
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
all planets orbit the Sun in the same direction – counter clockwise (ccw)(as viewed from above
North Pole)
all orbits lie in nearly the same plane
almost all planets have nearly circular orbits (Mercury is a minor exception)
most planets rotate ccw (Venus and Uranus are exceptions) including the Sun
most moons orbit their planet in same direction as the planet's rotation and orbit in their planet's
equatorial plane
-Mercury and Venus have no moons
-Earth has one and Mars has two very small asteroid-like moons
-The Jovian planets, by contrast, have many
-Jupiter is listed as having 6 but it actually has over 60
-Saturn has almost as many and Uranus and Neptune have 40 between them.
-All Jovian planets have ring systems
-Saturn’s rings are made of ice particles
-The rings of Jupiter, Uranus and Neptune are made of dark rocky particles
-Terrestrial planets have no rings
Asteroids lie primarily between Mars and Jupiter and a fairly broad belt in the same plane as planetary
orbits.
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Comets follow either elliptical orbits or parabolic/hyperbolic orbits passing close to the Sun once
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Made largely of ices mixed with rocky dust, no bigger than a few km across
Come from two major sources – the Kuiper belt (a doughnut shaped region starting around
Neptune and extending out into space) and the Oort Cloud (a spherical region completely
surrounding the solar system and extending out some 50,000 AU)
As a comet gets close to the Sun it generates a coma (an atmosphere of escaping gases and dust)
around its nucleus and two tails: a plasma tail of ionized gas swept away by the solar wind, and
a dust tail of small solid particles created by the escaping atmosphere (escapes from the comet
because of its weak gravity)
When we see a comet in the sky we don’t actually see its core but rather the lengthy beautiful tail
emanating from the core. This tail always points away from the Sun.
-During each pass of the Sun, comets lose material through sublimation and tail formation.
Meteoroids, Meteors and Meteorites are found around Earth
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Meteors are actually small bits of rock and/or metal falling into Earth’s atmosphere that heat up
due to friction with the air - “shooting stars” (of course, they are not stars at all)
A meteoroid is what the rocky object is called before it hits the atmosphere and becomes a
meteor
If the meteoroid is massive enough to have any part of it left before it hits the Earth’s surface it
then becomes a meteorite
Kuiper Belt – begins at about orbit of Neptune and extends out to about 100 AU

this doughnut-shaped belt lies mainly in the planetary or ecliptic plane
Oort Cloud – a spherical cloud surrounding solar system, centred on Sun, and comets from this region
come into solar system from all directions

Extends from the outer part of the Kuiper belt to about halfway to nearest stars
Half-Life – the time it takes for half of the atoms to decay in a radioactive element

Solar system formed about 4.6 billion years ago
Summary
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Orbital Radius (AU)
0.39
0.72
1.0
1.52
5.2
9.54
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Uranus
Neptune
19.2
30.1
Galactic Recycling Process – when stars die, the spew out their mass into the universe and the next
generation of stars contains some of these heavier elements and, in the process of formation, make some
new ones of their own
As the nebula started to contract around its centre, collapsing under its own gravity to something around
200 AU in diameter, three things occurred:
1. Temperature Increased
2. Nebular Rotation Rate Increased
3. Nebular Sphere Flattens to Disk
-Eventually as we move away from the Sun, the temperature drops to the freezing point for water (273K)
signifying a special point known as the ice or frost line
-Beyond the frost line, gaseous compounds such as ammonia and methane can condense to form ice
flakes that formed the basis for the Jovian planets
Condensation – adding one atom or molecule at a time
Accretion – small flakes of metal and rocks stick together by being closer to each other
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
in the inner solar system, where only metal and rocks and silicates could condense, planetesimals
were made of rocks and metals and formed the terrestrial planets — furthermore, as only rocks
and metals could condense the terrestrial planets were rich in these materials
in the outer solar system where ices could condense (it was cold enough) planetesimals were built
of ices and metals and rocks but because ice derivatives (H, He, methane, ammonia, etc) were
more abundant the planetesimals were based on these materials and collected more material,
becoming larger, forming the Jovian planets
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Solar Wind
-Once the protosun formed into the Sun that it is today, it generated a continuous emission of energetic
charged particles (electrons, protons, ions) spewing out in all directions from the Sun
-The formation of the eight planets continued as all of them were bombarded by asteroids, meteors and
comets
-The large Jovian planets experienced asteroid bombardment, but because of their atmospheres, no
evidence remains
-The asteroids in the “belt” between Mars and Jupiter are likely a collection of leftover planetesimals that
never quite made it as another planet
-Planetesimals were likely of two types:
(1) rocky and metallic (much like the inner planets)
(2) ice and hard snow embedded with small amounts of rock/metal (much like core of the Jovians)
-Our Moon may have formed as a result of a collision between Earth and a large, leftover planetesimal,
possibly as big as Mars
-The smaller mass results in its inability to retain any atmosphere.
Two main techniques are used to measure the motion of a star back-and-forth, or side-to-side, which hare
caused by the gravitational tugs of one or more planets.
a) The Astrometric Technique - the use of sensitive telescopes
b) Doppler Technique – the light coming from the star is tracked using
the gravitational tug it exerts on the star
c) Transit – as the planet moves in front of its star, the star’s luminosity
dips, and then returns to its former level when the transit is complete
-Very few planets orbit their parent star with a greater radius
than 5 AU
-Many orbits are quite elliptical
Planetary Migration – a scenario which allows the
formation of Jovian planets at expected distances from the
star (beyond the frost line) followed by a migration into an
orbit which brings the planet closer to the home star
Encounters and Resonances – a situation where a planet interacts gravitationally with other planets,
essentially a re-arrangement of the solar system objects
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Comparing the Terrestrial Worlds:
Earth’s Interior
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Core: highest density; nickel and iron
Mantle: moderate density; silicon, oxygen, etc.
Crust: Lowest density; granite, basalt, etc.
A planet’s outer layer of cool, rigid rock is called the lithosphere. It “floats” on
the warmer, softer rock that lies beneath the surface
Seismic Waves
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P waves push matter back and forth
S waves shake matter side to side
P waves go through Earth’s core but S waves don’t
Earth’s core must have a liquid outer layer
Reasons for layers: Differentiation
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Gravity pulls high density materials to center
Lower-density material rises to surface
Material ends up separated by density
Heating of Interior:
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Accretion and differentiation when planets were young
Radioactive decay is most important heat source today
Interior heat drives geological activity
Cooling of Interior
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Convection- transports heat as hot material rises and cool material falls
Conduction- transfers heat from hot material to cold material
Radiation-sends energy into space
Role of Size in Heating and Cooling:
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
Smaller worlds cool off faster and harder earlier
Mercury and the Moon are now geologically “dead” since their interiors have
cooled down
Sources of Magnetic Fields


A world can have a magnetic field if charged particles are moving inside
3 requirements:
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o Molten interior
o Convection
o Moderately rapid rotation
Processes that Shape Planetary Surfaces
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Impact cratering
o Impacts by asteroids or comets
Volcanism
o Eruption of molten rock onto surface
Tectonics
o Disruption of a planet’s surface by internal stresses
Erosion
o Surface changes made by wind, water, or ice
Impact Cratering:
 Most cratering happened soon after solar system formed
 All planets equally impacted
 Craters are about 10 times wider than object that made them
 Small craters generally outnumber large ones
 A surface with many craters has not changed much in 3 billion years
 Erosion can erase craters
Volcanism:
 Volcanism happens when molten rock (magma) finds a path through lithosphere
to the surface
 Molten rock is called lava after it reaches the surface
 Volcanism also releases gases from interior into atmosphere: outgassing
Tectonics:
 Convection of the mantle creates stresses in the crust called tectonic forces
 Compression forces make mountain ranges
 Valley can form where crust is pulled apart
 Earth’s continents slide around on separate plates of crust: plate tectonics
Erosion:
 Weather-driven processes that break down or transport rock
Comparison of Planetary surfaces
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Mercury and the Moon
o Heavily cratered
o Some volcanic plains
Venus
o Volcanoes and bizarre bulges
Mars
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o Volcanoes and canyons
o Apparently dry riverbeds
Geology of Earth
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Most active geology volcanoes and tectonics
Moderate atmosphere
Water in liquid state
Earth’s crust is divided into moving sections called plates
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Telescopes
Telescopes:
 A type of light collecting device
 Light rays can be reflected (bounced off) or refracted (bent) at an interface
between two materials
Lens:
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A lens has usually two refracting surfaces
If the surfaces are close, we have a thin lens
Refraction can cause parallel light rays to converge to a focus
The focal plane is where light from different directions comes into focus
The image behind a single (convex) lens is actually upside down. Your brain
flips the image
Basic designs of telescopes:
 Refracting telescope: focuses light with lens (Galileo)
o Need to be very long, to maximize the distance between the lenses
o They have large, heavy lenses for good light collection
 Reflecting telescope: focuses light with mirrors (Newton)
o Reflecting telescopes can have much greater diameters
o Modern telescopes (built after 1900) are reflectors
What are the advantages of a reflecting telescope over a refracting telescope?
 Only the reflecting surface of mirrors in a reflecting telescope have to be
perfectly shaped. In a lens the entire shape of the lends and both surfaces are
important
 Objective lenses are heavy and difficult to stabilize at the top of the telescope.
Heavy mirrors at the bottom of the telescope are less problematic
 Small telescopes can use other focal arrangements that would be difficult in
larger telescopes
 Lenses have chromatic aberrations that must be corrected
Two most important important properties of a telescope:
 Light collecting area: Telescopes with a larger collecting area can gather a
greater amount of light in a shorter time
 Angular resolution: Telescopes that are larger are capable of taking images
with greater detail
Angular Resolution:
 The minimum angular separation that the telescope can distinguish
 Also known as resolving power
 Ultimate limit to resolution comes from interference of light waves within a
telescope
 The is blurring called a diffraction fringe around every point of light in the
image (Cannot see any detail smaller than the fringe)
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This limit on angular resolution is known as the diffraction limit
Larger telescopes are capable of greater resolution because there is less
inference
Diffraction limit depends on the wavelength of light and diameter of the
telescope
Imaging:
 Astronomical detectors generally record only one colour of light at a time
 Several images must be combined to make full-colour pictures
 Columns of cool interstellar hydrogen gas and dust that are also incubators
for new stars
 Turbulent air flow in Earth’s atmosphere distorts our view, causing stars to
appear to twinkle
Spectroscopy:
 A spectrograph separates the different wavelengths of light before they hit
the detector
 Since the light is separated out, more total light (longer exposure times) is
required for the same telescope to make a spectrum than to make an image
 Spectroscopy gives information about:
o Composition of stars and nebulae
o Temperature of stars
o Motion of stars and galaxies (Doppler shift)
Transmission in atmosphere:
 Only radio and visible light pass easily through Earth’s atmosphere
 We need telescopes in space to observe other forms
 Space telescopes also avoid the problems of light pollution and atmospheric
turbulence
How can we observe nonvisible light?
 A standard satellite dish is essentially a telescope for observing radio waves
Interferometry:
 A technique for linking two or more telescopes so that they have the angular
resolution of a single large one
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Lecture 4 Notes
a) Mercury
- moderately high orbital eccentricity (0.206) meaning its orbit is observably elliptic
- orbital inclination is also high (7 degrees), greater than all others except Pluto
- rotational axis tilt is 0 degrees; no seasons on Mercury
- orbital period: 88 days, synodic period of 116 days (time between successive conjunctions with Earth)
- solar day of 176 Earth days
-The two elongations, eastern and western, are the greatest angular
positions the inner planet ever has with respect to Earth
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Elongations = angle between sun and planet from earth
-The two conjunctions, superior and inferior, refer to when Mercury is
lined up with the Earth and the Sun
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When the order is Earth-Sun-Mercury, we have a superior
conjunction
When Mercury is between the Sun and Earth, we have an
inferior conjunction  see a solar transit during an inferior conjunction
- not tidally locked to the Sun; rotates one and a half times during each orbit
- a solar day on Mercury (sun rise to sun rise) is 176 Earth days long (rotates very slowly)
- about 61% iron and has an iron core about 75% of the radius of the planet
- surface has craters everywhere
- very thin atmosphere, too small to retain any gas
- the iron core makes up about 42% of its volume, magnetic field is similar to Earth’s in shape but only
about 1% as strong
- Mariner 10 visited Mercury in the 70s, but it is very difficult to explore due to high temperatures
b) Venus
- orbital eccentricity of 0.0068, almost a perfect circle; greatest elongation is 47 degrees away from Sun
- brightest object in sky other than Sun and Moon; 16x brighter than any star because it is close to the
Sun, close to Earth, relatively large (about same as Earth), and its albedo is 0.59
- during an inferior conjunction, it is possible to have a solar transit of Venus
- Venus’ rotation is retrograde; it rotates backwards very slowly
- sidereal day that is 243 Earth days, orbital period 224.7 days, and solar day of 117 Earth days
- axial tilt is 177.4 degrees; north pole points downward; rotational axis of 2.6 degrees (no seasons)
- 740 K - dry, hot, uninhabitable desert, two large highland features: Ishtar Terra and Aphrodite Terra
- no tectonic activity, evidence of volcanic activity, erosion, no current bombardment
- atmosphere is 90 times as dense as Earths, lots of CO2 and water vapour in atmosphere
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- greenhouse effect causes there to be no water
- no magnetic field due to slow rotation; no protection from solar wind generates thick atmosphere
c) Earth
- orbit is almost circular (e = 0.017)
- average distance from Sun is 1 AU, takes 365.25 days to orbit the Sun
- rotational axis inclined at 23.5 degrees causing seasons
- slightly bigger than Venus, radius of almost 6400km
- average surface temperature is 9 degrees Celsius; range is 60 to -90 degrees Celsius
- one natural satellite, the Moon, which orbits Earth in 29.5 days (solar period)
- atmosphere of nitrogen and has a magnetic field
- core is surrounded by a molten shell, thick mantle, and a thin crust
- lithosphere is about 100km thick, covered with liquid water (75%) and solid land mass (25%)
- two main seismic waves are p-waves (primary) which are pressure waves and s-waves (secondary)
which are shear waves; solid inner core of radius 1300km surrounded by 3500km molten outer core
- centre is around 6,000K, rich in nickel and iron
- crust consists of granite and rocks, upper mantle largely iron-magnesium-silicate mixture
- changing surface due to volcanic activity, plate tectonics and erosion
- melting point within the mantle is well above the actual temperature, so mantle is solid
- continental drifts causes plates to move slowly forming mountains, ocean ridges, new land
- atmosphere is unique, 77% nitrogen, 21% oxygen, 1% argon, some water and carbon dioxide
- temperature is cool enough to allow water vapour to condense as rain
- CO2 dissolves in water so oceans hold some of it and rainfall carries minerals from rocks/land into the
ocean which react with dissolved CO2 to form carbonate minerals which fall to ocean floor
- oxygen originally built up in atmosphere when only planets existed and few animals used it up
- very strong magnetic field resulting “magnetosphere” extending beyond the atmosphere
- at 3000 and 20,000km above Earth’s surface are two zones of trapped, charged, high-energy particles
called the Van Allen belts surrounding the Earth centred on the magnetic equator
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
Particles are from solar wind and these belts protect life on Earth from the harmful effects of the
solar wind particles
- aurora borealis in the North and aurora australis in the South are caused by these particles
d) The Moon
- average distance from Earth to Moon is 384,400 km
- sidereal period is 27.3 days, but takes 29.53 days to move through phases due to Earth’s orbit
- tipped at 6.7 degrees, size is 0.27 of Earth
- large dark areas on the surface are called maria, and lighter-coloured regions are called highlands
- the lunar highlands are covered with hundreds of craters
- large water ice deposits near both poles have been detected, which likely came from meteoroids
- largest crater in Solar System discovered on far side of the moon, 2500km wide, Aitken Basin
- Neil Armstrong set foot on the Moon on July 20, 1969
- virtually no atmosphere, low escape speed so any gas molecules eventually leave
- no erosion and no tectonic action so surface changes very, very slowly
- no global magnetic field
- large impact hypothesis theory imagines a collision between a very young, molten Earth and a large,
Mars-like object where debris particles in a ring began to accelerate into larger bodies
- plans exist to establish human colonies on the Moon for further exploration, mining, and scientific
research
e) Mars
- average orbital radius of about 1.5 AU with a relatively large eccentricity
- fairly bright but less than Venus due to smaller size, distance from Sun and lower albedo of 0.15
- rotation is similar to Earth’s, around 24.6 hours, and tipped at about 24 degrees resulting in seasons
- radius about 50% of Earth and mass about 10% but with a density 70% of Earth
- polar ice caps made of CO2 or dry ice, NOT water, although water ice below surface of poles
- huge volcanoes (largest in solar system), deep canyons, huge dune fields
- lava flows in the north, Tharsis bulge contains volcanoes, Valles Marinis canyon rises 10km high than
any other part of planet, Olympus Mons (largest volcanoe) is 600km in diameter and rises 21km
- no tectonic activity, volcanoes are inactive
- the Vallex Marineris canyon was formed when the planet’s surface bulged out under the forces of
crustal formation, is about 4000 km long, 120km across at widest point, 7km deep in some areas
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- the canyon was NOT created by water flow or tectonics but rather by heat conduction forces
- two Mars rovers called Spirit and Opportunity (which is still functioning)
- significant evidence of previous presence of water on Mars
- very thin atmosphere with a pressure of about 1/150 that of Earth
consisting of mostly carbon
dioxide (95.3%) and other gases
- "Mars apparently was once a world with pleasant temperatures
and streams, rain, glaciers, lakes and possibly oceans. It had all the
necessities for life as we know it. But the once hospitable planet
turned into a frozen and barren desert at least 3 billion years ago,
and it is unlikely that Mars will ever be warm enough for its frozen
water to flow again. If life once existed on Mars, it is either extinct
or hidden away in a few choice locations, such as hot springs
around not-quite-dormant volcanoes. As we think about the
possibility of future climate change on Earth, Mars presents us with
an ominous example of how much things can change."
- no magnetic field although there likely was once a field generated by moving, liquid, iron core
- Mars has two small moons: Phobos and Deimos; only few km across and gravity too low for them to by
spherical (Phobos orbits in 7 hours and 39 minutes and Deimos around three days)
- Mars radius is about 3400km, Phobos orbits 9378km from center and Deimos 22460km
- the moons may be captured asteroids or have formed from interplanetary debris during formation
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Stars and Constellations
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When you look up at the stars you look out through a layer only about 100
km deep
With the naked eye, we can see more than 2000 stars plus the milky way
Ancient civilizations named groups of stars called constellations
Names were based on ancient heroes, gods, animals, shapes, and mythology
was associated with them
Many star patterns recognized today originated 5,000 tears with the
Babylonians, Egyptians and later the Greeks
In 1928, the International Astronomical Union (IAU) established 88 official
constellations with clearly defined permanent boundaries that together
cover the entire sky
Just like a map of the earth is divided into countries, a map of the sky is
divided into constellations
A constellation now represents not a group of stars but a section of the sky –
a viewing direction
Any star within the region belongs to only that one constellations
The sky also contains some star groupings called asterisms
Example:
o Big dipper in the constellation Ursa Major (the Great Bear)
o Great square of Pegasus
The brightest stars in a constellation may actually be quite far away from
each other
Constellations:
 Most constellations are made up of stars that are not physically close to one
another
 Some stars may be moving in different directions
Star Names:
 Most individual star names derive from ancient Arabic, Greek, or Latin,
altered over centuries
 Examples:
o Sirius: Greek meaning glowing
o Vega: Arabic meaning landing (constellation was viewed as a
landing vulture)
o Spica: Latin from spica virginis meaning the ear of wheat of virgo
 Another way to identify stars is to assign Greek letters to the bright stars in a
constellation in the approximate order of brightness
 Astronomers measure the brightness of stars using the magnitude scale
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Modern instruments measure the flux: the total light energy hitting one
square metre per second
Flux can then be used to calculate apparent visual magnitude
Some stars are so bright they have negative magnitudes
Faint stars detected by telescopes have magnitudes larger than 6
Apparent visual magnitude is based only on visible light
Apparent visual magnitude does not measure energy
The Celestial Sphere:
 The celestial sphere is useful for describing the location (but not distance) of
stars in the sky – does not really exist
 Ecliptic is Sun’s apparent path through the celestial sphere
Angular Distance:
 Measured in degrees
 An object’s angular size appears smaller if it is father away. This relationship
is very useful for calculating actual distance or sizes
 Angular size = physical size x 360 degrees
2(3.14) x distance
Specifying Locations on Earth:
 Latitude: position on Earth north or south of equator
 Longitude: position on Earth east or west of prime meridian (runs through
Greenwich, England)
 Longitude helps us determine universal and local time
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Planets
The Sun:
 Radius: 108x radius of Earth (695,700km)
 Distance to earth = 149.6M km
 Mass: 333, 000 x mass of Earth
 Over 99.9% of solar system’s mass
 Surface temperature 5800 K
 Composition: 98% hydrogen and helium, 2 other elements
 In 1 second the Sun produces a million the total energy used in the US in ne
year
 Star at center of solar system
Earth:
 Distance from sun = 149.6M km
 Radius = 6,371km
 Oasis of life
 The only surface liquid water in the solar system
 A surprisingly large moon
 Third planet from Sun
 Densest planet of solar system
 Largest out of 4 terrestial planets
Mercury:
 0.4 AU from sun
 0.38 x radius of Earth
 0.055 x mass of Earth
 Made of metal and rock; large iron core, no atmosphere
 Desolate, cratered
 Very hot and cold 425 C (day), -170 C (night)
 Rotates 3 times in every 2 orbits around the sun
Venus:
 0.7 AU from sun
 0.95 x radius of Earth
 0.82 x mass of Earth
 Extreme greenhouse effect: Hotter than Mercury: 470 C, day and night
 Atmospheric pressure like 1km underwater
 No oxygen or water
 Rains sulfuric acid
Mars:
 1.5 AU from sun
 0.53 x radius of Earth
 0.11 x mass of Earth
 Looks almost Earth-like
 Giant volcanoes, a huge canyon, polar caps…etc.
 Water flowed in the distant past, could have been life?
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Jupiter:
 5.2 AU from sun
 11.2 x radius of Earth
 318 x mass of Earth
 Much farther from Sun than inner planets
 Most H/He; no solid surface (all gas)
 300 times more massive than Earth
 Many moons
o Io: Active volcanoes al over
o Europa: possible subsurface ocean
o Ganymede: Largest moon in solar system
o Calisto: a large, cratered ice ball
 Jupiter has rings
Saturn:
 9.5 AU from sun
 9.4 x radius of Earth
 95.2 x mass of Earth
 Giant and gaseous like Jupiter
 Spectacular rings made of ices and rocks
 Many moons, including cloudy Titan
 Cassini spacecraft currently studying it
Uranus:
 19.2 AU from Sun
 4 x radius of Earth
 14.5 x mass of Earth
 Smaller than Jupiter, Saturn; much larger than Earth
 Made of H/He gas & hydrogen compounds
 Extreme axis tilt
 Moons and rings
Neptune:
 30.1 AU from sun
 3.9 x radius of Earth
 17.1 x mass of Earth
 Similar to Uranus (except axis tilt)
 Many moons including Triton
 Has rings
Pluto:
 39.5 AU from sun
 0.18 x radius of Earth
 0.0022 x mass of Earth
 Much smaller than other planets: dwarf planet
 Icy, comet-like composition
 Its moon Charon is smaller in size
 The plane of its orbit is tilted other dwarf planets: Eris, Ceres
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Small Bodies in the solar system:
 Small bodies, the leftover scraps from the formation of the Solar System,
fall into three distinct groups:
o 1. Asteroids
 Rocky or metallic in composition
 Most are located between the orbits of Mars and Jupiter
o 2. Kuiper belt comets
 Made mostly of ice
 Orbit the Sun beyond Neptune
 Orbit in same direction and plane as the planets
o 3. Oort cloud comets
 Mode mostly of ice
 Orbit at the out fringe of the Solar System
 Spherically distributed about the Sun
Properties of Asteroids:
 Small in size
 Not spherical
 All the asteroids in the solar system wouldn’t even add up to a small
terrestrial planet
 Meteor – a trail of light cause by a particle which enters Earth’s atmosphere
o Most particles are the size of a pea
o Completely burn up in Earth’s atmosphere
 Meteorite – a rock which is large enough to have survived its fall to Earth
o Cause a brighter meteor, sometimes called a fireball
o Have higher metal content than terrestrial rocks
o Contain Iridium and other isotopes not found in terrestrial rocks
Comets:
 Icy
 Not confined to the ecliptic and disappear after several weeks
 Most comets remain perpetually frozen in the outer solar system
 Only comets that enter the inner solar system grow tails
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Jovian Planet Systems
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Voyager and explored the outer planets in the ’s and ’s
The Galileo spacecraft circled Jupiter dozens of times in the
’s
The Cassini Huygens orbiter and probe arrived at Saturn in 2004
Planet origins:
o Low density because they formed in the outer solar nebula where
water vapour could freeze to form ice particles
o Ice accumulated in proto-planets with density lower than rocky
terrestrial and asteroids
Compared to terrestrials:
o Much larger and more massive
o Composed mostly of hydrogen, helium
Inside Jovian Planets:
o All cores appear to be similar
 Made of rock, metal, and Hydrogen compounds
 10x the mass of Earth
o Uranus and Neptune captured less gas from the Solar nebula
 Accretion of planetesimals took longer
 Not much time for gas captures before nebula was cleared out
by Solar wind
o Only Jupiter and Saturn have high enough pressure for H & He to exist
in liquid and metallic states
Jupiter and other Jovian planets are all slightly flattened
A world with a large rocky core and mantle would not be flattened much by
rotation
An all-liquid planet, though, would flatten significantly
Jupiter:
o Largest and most massive of the Jovian planets
o Contains 71 percent of all the planetary matter in the entire solar
system
o It emits about twice as much energy as it absorbs from the sun
(energy left over from the formation of the planet)
o Hydrogen compounds in Jupiter form clouds
o Different cloud layers correspond to freezing points of different
hydrogen compounds
o Like Earth, Jupiter has circulation cells in its atmosphere
o Jupiter is much larger and rotates faster
o Circulation cells are split into many bands of rising and falling air
(stripes)
o The so-called:
 Zones (rising air)
 Belts (Falling air)
Other Jovian planets have cloud layers similar to Jupiter’s
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The temperature profile of each planet determines the colour of its
appearance
Why Uranus and Neptune are blue:
o They have a higher fraction of methane gas, which absorbs red
sunlight
o Blue light is reflected back into space by the clouds
Jovian Storms:
o All the Jovian planets have strong winds and storms
o Jupiter’s Great Red Spot: a storm that has existed for at least
years
Jovian Magnetospheres:
o The strong magnetic field around Jupiter traps particles from the solar
wind in lethal radiation belts a billion times more intense than the
Van Allen belts that surround Earth
o Other planets have smaller and weaker magnetospheres
o Fraction of electrically conducting material in interiors is smaller
o Solar wind is weaker father out, or else their magnetospheres would
be even smaller
o We cannot fully explain the magnetic filed tilts of Uranus and Neptune
Saturn:
o From spacecraft flybys, we see thousands of individual rings
 Separate by narrow gaps
 They differ in brightness and transparency
o From within the rings, we would see billions of individual particles
 Size ranges from house sized to dust
 Made of snowballs
 Many collisions keep rings thin
Ring Formation:
o Jovian planets all have rings because they possess many small moon
o Rings formed from random impacts on moons
o Gravitational force of Saturn and moons prevent the debris from
becoming larger moons
o Saturn’s rings may be due to recent impact
o Rings thin out from impacts and radiation
o The rings orbit inside the Roche limit
o Raw material for a moon cannot coalesce inside the Roche limit due to
the gravitational forces of the planet
o Compared to Saturn, the other ring systems
 Have fewer particles
 Are smaller in extent
 Have darker particles
o Other unsolved mysteries:
 Uranus’ rings are eccentric and slightly tilted
Uranus:
o Discovered in 1781 by William Hershel
o Atmosphere is over
degrees colder than Jupiter’s
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o The mantel contains rocky material and dissolved ammonia and
methane
o Circulation in this electrically conducting mantel may generate the
planet’s peculiar magnetic field – which is highly inclined to its axis of
rotation
Neptune:
o Existence and location of Neptune was predicted from irregularities in
the motion of Uranus
o Discovered in 1846
o Same size and interior as Uranus
o Atmosphere contains 1 and a half times more methane than Uranus:
bluer
Jovian Moons:
o Small moons – not spherical, probably captured asteroids
o Medium moods – 300 to 1500 km in diameter
o Large moons – greater than 1500 km in diameter
o Both groups formed in orbit around Jovian planets
o Enough self gravity to be spherical
o Have substantial amounts of ice
o Jupiter Moons:
 Io – sulfur volcanoes
 Europa – world of water ice (and liquid)
 Ganymede – active ice world
 Calisto – dead and dirty ice world
o Saturn Moons:
 Titan – only moon to have a thick atmosphere, so cold that is
gas molecules do not travel fast enough to escape, consists
mostly of nitrogen, liquid-methane
o Neptune’s Moons:
 Triton – orbits the opposite direction, thin nitrogen
atmosphere, some sort of volcanic activity has occurred
Rocky planets versus icy moons:
o Rock melts at higher temperatures
o Only rocky planets have enough heat for geological activity
o Ice melts at lower temperatures, so less heating is required to have
molten cores. Volcanism and tectonics can occur
o Tidal heating can melt internal ice,
The moons of Jupiter become less dense as you get farther from Jupiter
o Mini Solar System
Gravitational tidal heating due to resonances keeps interiors of the inner
moons hot
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Speed of Light
Why is the speed of light the cosmic speed limit?
Why is it a big deal to break the speed of light barrier?
What did scientists observe at CERN?
-Einstein’s Theory of Relativity (1905)
-General Theory of Relativity (1915)
-Relativity of Motion
 Motion is not absolute – we must measure speed of one object relative to one
another
Reference Frames (Point of View):
 Two or more objects which don’t move relative to each other share the same
reference frame
 Objects moving relative to one another are in different reference frames ex. Plane
and the ground below
 An inertial reference frame is one that is not accelerating. IT is at rest or moving
at constant velocity
 Motion can be defined with respect to a particular frame of reference
-Speed of light “c” (300,000 km/s) speed of light is always the same, cannot increase or
decrease
Rules of Special Relativity:
 The laws of nature are the same in all inertial reference frames
 The speed of light is the same in all inertial reference frames
Consequences of Special Relativity:
 Time slows down for moving objects
 Lengths shorten for moving objects
 Mass of a moving object increases
 Energy and mass are related
 Simultaneity of events depends on your reference frame
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Length Contraction:
 The time taken to travel between two points is shorter to a moving observer
because of time dilation
 The length of the journey is thus contracted
 Length contraction occurs along the direction of motion
 Length contraction is symmetric
Mass Increase:
 A force (push or pull) applied to a rapidly moving object procures less
acceleration than if the object were motionless
 This effect is like a mass increase in the moving object
The Speed of Light Barrier:
 The faster the object is moving, the less acceleration is produced by the force
 When the object is moving at the speed of light, the force produces zero
acceleration
 The object cannot go faster
 Example: the distance to Vega is about 25 light years. But if you could travel to
Vega at 0.999c, the round trip would seem to take only 2 years.
Breaking the speed of light barrier:
 Violates the law of special relativity
 These laws have confirmed in many other experiments
 Could question our understanding of time and space
 Could question our understanding of the relationship between energy and matter
 Has implications for the laws of cause and effect
 Could redefine cosmology (structure and evolution of the universe)
 Could point towards new fundamental theories of nature and ways to come up
with a grand unified theory
Large Hadron Collider:
 The world’s largest particle accelerator
 Located at the French – Swiss border about 100m below ground
 Produces high energy collusions of fundamental particles such as protons
 Particles are accelerated at 99.999999% of the speed of light
 Run by CERN
 The world wide web was first created at CERN in 1989
 OPERA experiment – neutrinos from CERN were sent to Italy’s INFN Gran Sass
Laboratory 730 km away. Particles were detected to arrive 60 nanoseconds earlier
than predicted by the speed of light (traveling roughly 60 feet further than light
every second)
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All About Stars
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100 billion stars in our galaxy
100 billion galaxies
The size of the observable universe is roughly
130,000,000,000,000,000,000,000 km
Some commonly used distance units:
o 1ly (light year) is the distance light travels in 1 year
o Speed of light = 300,000 km/s
o In 1 second sight travels 300,000km
o The astronomical unit (au)
o The earth’s orbit around the sun is elliptical. Hence the distance
between the earth and sun varies at different points
o 1 au = Average distance between earth and sun
 What is the size of the earth in astronomical units?
150,000,000 km = 1 au
130,000,000,000,000,000,000,000 km
= (1au/150,000,000 km) x 130,000,000,000,000,000,000,000 km
=8,666,666,666,667 au
=Roughly 8.67 trillion au (NOW. The universe is always expanding)
 What is the size of the earth in light years?
9,460,000,000,000 km = 1 ly
130,000,000,000,000,000,000,000 km
= (1ly/ 9460,000,000,000km) x 130,000,000,000,000,000,000,000 km
= 13,742,071,882 ly
= roughly 14 billion ly
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Scientific Notation: every number can be expressed as a multiple of powers
of 10
o Place the decimal after the first nonzero digit
o Count the number of places that the decimal point moved. This gives
the power of 10.
o If the decimal moves to the left, the power is positive. If the decimal
moves to the right the power is negative
o Ex. 4812=4.812 x 1000=4.812 x 103
o Ex. 0.0000312= 3.12 x 1/100000 = 3.12 x 10-5
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The cosmic calendar:
Say we speed up our clocks by a factor of 13.6 billion.
o The entire age of the Universe would be one calendar
o One month would be approximately 1 billion years
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Events:
o Big Bang: 13.6 billion years ago (January)
o Milky Way Galaxy forms: 8.8 billion years ago (March/April)
o Sun and planets form: 4.6 billion years ago (August)
o First life forms: 3.8 billion years ago (September)
o First dinosaurs: 300 million years ago (December 24)
o First mammals: 200 million years ago (December 25)
o Extinction of dinosaurs: 65 million years ago (December 29)
o First apes: 15 million years ago (December 31)
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Earth is roughly 4 billion years old
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The Nature of Light
- The warmth of sunlight tells us that light is a form of energy: radiative energy
- Units of energy: joules
- We can measure the flow of energy in light in unit of watts: 1 watt=1joule/s
- Newton showed white light is made up of many different colours
- Quantum Mechanics: Light behaves as both, particle and wave
- A wave is a periodic motion that can carry energy without carrying matter along with it
- Light is an electromagnetic field
 Light wave is a vibration of electric and magnetic fields
 Light interacts with charged particles
- Wavelength and frequency
 Wavelength x frequency = speed of light = constant
 Speed of light is 300,000,000 m/s
 Thus lower wavelength means higher frequency and vice versa
 Wavelengths/frequencies are related to colour
 Longer wavelengths/lower frequencies: redder light
 Short wavelengths/higher frequencies: bluer light
- The electromagnetic spectrum
 Visible 400-700 nanometers
 Highest frequency waves – gamma rays, x-rays
 Lowest frequency waves – radio waves
 Energy and wavelengths are inversely related
- Interactions of light with matter:
 Emission – energy in matter can be converted into light that is emitted
 Absorption – matter absorb energy in the form of light and convert it to another
form or re-emit it
 Transmission
 Reflection or Scattering
 We see objects the emit light directly
 We see others by light reflecting off these objects
- The structure of matter
 Atoms are the building blocks of matter
 Every element is made up of a different type of atom
 All atoms are made of
o
Protons with positive charge of +1
o
Neutrons with 0 charge
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o
Electrons with a negative charge -1
 The size of an atom is less than 1 millionth of a millimeter
 The nucleus is 100,000 times smaller in size but incredibly dense
 The nucleus contains most of the mass of the atom: protons and neutrons
- Mass of protons and neutrons is 2000 times the mass of electrons
- Light = cosmic messenger
 Light travels to us from all parts of the universe
 Matter in the universe interacting with light leaves its fingerprints in the light
 Spectroscopy is the process of dispersing light into its spectrum (different
wavelengths)
- Emission Line Spectrum
 A thin or low-density cloud of gas emits light only at specific wavelengths
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Jovian Planets – Jupiter, Saturn, Uranus, Neptune
-Jupiter, the largest, could hold 1400 Earths, Neptune, the smallest, could hold 50 Earths
-They all have rings, they have many moons (Jupiter over 60), composition of H and He (gas and liquid)
-They have huge atmospheres surrounding relatively small rocky cores
-Not perfectly spherical but flattened somewhat at poles due to fast rotation
-Obliquity, the inclination of a planet’s equator to its orbital plane, is minimal for Jupiter (3 degrees)
resulting in no seasons; tilt for Uranus is 98 degrees means it rotates backwards
-Generate more radiation than they receive from the Sun
-Temperature increases rapidly along with the pressure and density as one descends into Jupiter
 Quickly becomes liquid H and then an even more compact form becoming metallic H (a
conductor), which when combined with Jupiter’s rapid rotation generates a large magnetic field
-Central core is a mixture of hydrogen, rock and metals
-More mass would make Jupiter smaller as it results in a greater gravitational field
-Saturn is almost as big but only 1/3 the mass and low density such that it would float in water
-Cores are all about 10 Earth masses
Jupiter’s At osphere
-75% H, 24% He, 1% Hydrogen compounds (which make the planet visible)
-Cloud layers have different compositions which create alternating zones and belts resulting in
Jupiter’s colourful appearance
-The bands of rising air are zones and appear white because of ammonia clouds
-The adjacent bands of falling air are belts which are transparent
-The rising zones and falling belts result from pressure differences between regions
-Great Red Spot: long-lived high-pressure storm wider than two Earths
Satur , Ura us, a d Neptu e’s At osphere
-Saturn’s more subdued yellows, reds and tans come from the same compounds on Jupiter
 However, a lower temperature and deeper cloud layers result in a “washing out” of distinct colour
variations
-Uranus and Neptune are distinctly blue from the methane (20x more than on Jupiter/Saturn) which form
in icy flakes in the upper clouds
-All Jovian planets have weather patterns with storms and winds; greatest speeds on Saturn
-Neptune has one high-pressure storm seen as the Great Dark Spot
Magnetic Fields
-All Jovian planets have substantial magnetic fields and magnetospheres
-Jupiter’s magnetic field is about 20,000 times stronger than Earth’s so its magnetosphere deflects the
solar wind 3M km before it even reaches Jupiter
-Other planetary magnetospheres are smaller with Saturn's generated by its thinner layer of metallic
hydrogen, and Uranus' and Neptune's magnetic fields generated by their cores as they have no metallic
hydrogen layers
Jovian Moons and Rings
-More than 150 moons orbit the four Jovian planets
-Classified as small (<300km in diameter), medium (300-1500km) and large (>1500km)
-Most are categorized as small and are irregular in shape because gravity is too small to force them into a
spherical shape
 Many also have unusual orbits and some even revolve backwards
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-Most medium/large moons are spherical and some have atmospheres, hot interiors, magnetic fields
-Impact cratering has occurred on most moons, volcanism is present on some along with tectonics
Galilean Moons of Jupiter
a) Io – most volcanically active object in the solar system with 300 active volcanoes continually repaving
the surface; a 400,000 volt potential exists across the surface resulting in a 5M amp current
b) Europa – the smoothest body in the solar system, completely covered by water ice a few km thick
- lines covering the surface are fractures in the ice surface caused by tidal forces of Jupiter/other moons
c) Ganymede – largest moon in the solar system, similar in appearance to Callisto having impact craters
- both reveal the effect of tectonic action early in its formation; covered with an icy shield
Moons of Saturn
a) Titan - atmosphere is 90% N (only world besides Earth where N is the dominant gas)
- almost as large as Mars; hydrocarbon gases result in a greenhouse effect, cold -180 degrees C
- few craters on surface, evidence for ice volcanoes, seasonal variations with wind speeds
- wide variety of hydrocarbon molecules in the upper atmosphere
b) Enceladus – active geologically; energy, organics, liquid water are present
- unknown if life forms are contained in the deep oceans of water under the icy surface
Moons of Uranus
-Small and numerous; largest are likely composed of ice and rock
-Miranda is heavily cratered but unlike any other moon with its ridges, cliffs and valleys
Moons of Neptune
-Triton has a retrograde orbit inclined at 20 degrees
-Surface temperature of 37 K and a surface of water ice
-Total Moons: Earth – 1, Mars – 2, Jupiter – 67, Saturn – 62, Uranus – 27, Neptune – 13
Jovian Moons and Rings
-Rings of Saturn: A ring, B ring, C ring; small cap near edge of A ring is called Encke gap
-Particles making up rings vary in size from mere dust to boulder-sized water ice chunks
-Any ring particles that stray from circular orbits get nudged or pushed back into orbit by adjacent ring
objects to maintain the ring structure
-Rings begin at about 10,000 km from Saturn’s surface out to 420,000 km
-Rings are no thicker than 100 meters
-Critical distance inside which the moon is broken apart is known as the tidal stability limit or Roche
limit; Roche limit is about 2.4 times the radius of the planet
-Ring particles are constantly falling into the parent planet as the upper atmosphere extends into the ring
system; rings get replenished with new particles
-Some rings are so well-defined in space because of the influence of small moons that orbit on either side
of it and are known as Shepherd moons
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Calculations
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
100 billion stars in our galaxy
100 billion galaxies
The size of the observable universe is roughly
130,000,000,000,000,000,000,000 km
Some commonly used distance units:
o 1ly (light year) is the distance light travels in 1 year
o Speed of light = 300,000 km/s
o In 1 second sight travels 300,000km
o The astronomical unit (au)
o The earth’s orbit around the sun is elliptical. Hence the distance between
the earth and sun varies at different points
o 1 au = Average distance between earth and sun
 What is the size of the earth in astronomical units?
150,000,000 km = 1 au
130,000,000,000,000,000,000,000 km
= (1au/150,000,000 km) x 130,000,000,000,000,000,000,000 km
=8,666,666,666,667 au
=Roughly 8.67 trillion au (NOW. The universe is always expanding)
 What is the size of the earth in light years?
9,460,000,000,000 km = 1 ly
130,000,000,000,000,000,000,000 km
= (1ly/ 9460,000,000,000km) x 130,000,000,000,000,000,000,000 km
= 13,742,071,882 ly
= roughly 14 billion ly

Scientific Notation: every number can be expressed as a multiple of powers of 10
o Place the decimal after the first nonzero digit
o Count the number of places that the decimal point moved. This gives the
power of 10.
o If the decimal moves to the left, the power is positive. If the decimal
moves to the right the power is negative
o Ex. 4812=4.812 x 1000=4.812 x 103
o Ex. 0.0000312= 3.12 x 1/100000 = 3.12 x 10-5

The cosmic calendar:
Say we speed up our clocks by a factor of 13.6 billion.
o The entire age of the Universe would be one calendar
o One month would be approximately 1 billion years
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Events:
o Big Bang: 13.6 billion years ago (January)
o Milky Way Galaxy forms: 8.8 billion years ago (March/April)
o Sun and planets form: 4.6 billion years ago (August)
o First life forms: 3.8 billion years ago (September)
o First dinosaurs: 300 million years ago (December 24)
o First mammals: 200 million years ago (December 25)
o Extinction of dinosaurs: 65 million years ago (December 29)
o First apes: 15 million years ago (December 31)

Earth is roughly 4 billion years old
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Solar System
- Formation of the Solar System:
 The nebular theory states that our solar system formed from the gravitational
collapse of a giant interstellar gas cloud—the solar nebula
 Kant and Laplace proposed the nebular hypothesis over two centuries ago
 A large amount of evidence now supports this idea
 Predictions of this theory have been accurate
-The Birth of the Solar System:
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
Solar nebula was initially a cold low density cloud of gas of diameter 100-200 AU
Collapse of the gas may have been triggered by a cosmic event such as the shock
wave of a nebula
-Spinning Cloud:
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Initial slow rotation speed of the cloud increased as the cloud contracted (ice
skater)
The cloud heated up as it contracted
The sun formed at the center where temperatures and densities were highest
-Disks around other stars:

Observation of disks around other stars support the nebular hypothesis
-Motion in the Solar System:
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
The spinning disk explains the uniform motion observed in the solar system today
planets all orbit the same direction of the spin of the disk they were formed from
Planets orbit in the same plane because of the flattening of the disk they were
formed from
-Why are the two types of planets?
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Inner part of disks are hotter than outer parts
Rock can be solid at much higher temperatures than ice
Inside the ice line (frost line): too hot for hydrogen compounds to form ices.
Only rocks and metals can be solid
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
Out the ice line: cold enough for ices to form
-How did terrestrial planets form?
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Small particles of rock and metal (seeds) were present inside the ice line
Planetesimals of rock and metal built up as these particles collided. This process
is called accretion
o Many smaller objects collected into just a few large ones
o Computer simulations support this process
o Meteorites provide evidence of early condensation
Gravity eventually assembled these planetesimals into terrestrial planets over a
few million years
Heat cause melting and differentiation inside the planets
-How did Jovian planets form?
 Ice could also form planetesimals outside the frost line
 Larger planets may have been able to form from H and He gases by direct
gravitational collapse without an accretion phase
 Planets were large enough to draw in surrounding gas to form moons and rings
-What ended the era of planet formation?

Outflowing matter from the Sun – the solar wind – blew away the leftover gases
-Where did asteroids and planets come from?



Leftovers from the accretion process
Rocky asteroids inside frost line
Icy comets outside frost line beyond orbit of Pluto
-Asteroid Orbits:
 Most asteroids orbit in a belt between Mars and Jupiter
 Trojan asteroids follow Jupiter’s orbit
 Rocky planetesimals between Mars and Jupiter did not accrete into a planet
 Jupiter’s gravity stirred up asteroid orbits and prevented their accretion into a
planet
-Origin of Meteorites:

Primitive:
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
o About 4.6 billion years old
o Accreted in the Solar nebula
Processed:
o Younger than 4.6 billion years
o Matter has differentiated
o Fragments of a larger object which processed the original solar nebula
material
-Origin of Comets:
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
We can tell where comets originate by measuring their orbits as they visit the Sun
Most approach from random directions and do not orbit in the same sense as the
planets
o They come from the Oort cloud
Others orbit along the ecliptic plane in the same sense as the planets
o They come from the Kuiper belt
-Pluto: Dwarf Planet or Kuiper Belt Comet?
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By far the smallest planet.
Not a gas giant like other outer planets
Has an icy composition like a comet
Has a very elliptical, inclined orbit
Pluto has more in common with comets than with the eight major planets
Pluto is currently classified as a dwarf planet
Other dwarf planets: Ceres, Eris
-Other Icy Bodies:
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
Many icy objects like Pluto on elliptical, inclined orbits, beyond Neptune
The largest, Eris (previously planet X) discovered summer 2005, is even larger
than Pluto
-How to Explain Exceptions to the Rules:
Heavy bombardment:
 Leftover planetesimals bombarded other objects in the late stages of the Solar
System formation
Origin of Earth’s water:
 Water may have come to Earth by way of icy planetesimals from outer Solar
System
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Odd Rotation:
 Giant impacts may explain different rotation axes of some planets
Meteor Impacts and Mass Explosions:
 Meteor crater in Arizona cause by 50m asteroid
 Impact occurred 50,000 years ago
 65 million years ago many species, including dinosaurs, disappeared from Earth
Iridium - Evidence of an Impact:
 Very rare in Earth’s surface rocks but found in meteorites
 Worldwide layer containing iridium, laid down 65 million years ago, probably by
meteor impact
 Dinosaur fossils all lie below this layer
Impacts and Mass Extinctions on Earth:
 Debris in atmosphere blocks sunlight, plants die, animals starve
 Poisonous gas in atmosphere
-Planet Detection:
 Direct: Pictures of spectra of the planets themselves
 Indirect: measurement of stellar properties revealing the effects of orbiting
planets
-Surprising Characteristics of Detected Planets:
 First extrasolar planet detected in 1995
 Almost 700 extrasolar planets have been discovered so far
 Some have highly elliptical orbits
 Some massive planets orbit very close to their stars “hot Jupiters”
 This forces reexamination of Nebular theory – massive “Jupiter-like planets
should not form inside frost line (at < 5 AU)
 Planetary migration or gravitational encounters may explain Hot Jupiters
o Close gravitational encounters between two massive planets can eject one
planet while flinging the other into a highly elliptical orbit
o Multiple close encounters with smaller planetesimals can also cause
inward migration
-First Earth-like planet found:
 Discovered April 2007
 Orbiting the star Gliese 581 about 20.5 ly away
 Lies in habitable zone – may be water planet
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Planets
The Sun:
 Radius: 108x radius of Earth
 Mass: 333, 000 x mass of Earth
 Over 99.9% of solar system’s mass
 Surface temperature 5800 K
 Composition: 98% hydrogen and helium, 2 other elements
 In 1 second the Sun produces a million the total energy used in the US in ne
year
Mercury:
 0.4 AU from sun
 0.38 x radius of Earth
 0.055 x mass of Earth
 Made of metal and rock; large iron core, no atmosphere
 Desolate, cratered
 Very hot and cold 425 C (day), -170 C (night)
 Rotates 3 times in every 2 orbits around the sun
Venus:
 0.7 AU from sun
 0.95 x radius of Earth
 0.82 x mass of Earth
 Extreme greenhouse effect: Hotter than Mercury: 470 C, day and night
 Atmospheric pressure like 1km underwater
 No oxygen or water
 Rains sulfuric acid
Earth:
 Oasis of life
 The only surface liquid water in the solar system
 A surprisingly large moon
Mars:
 1.5 AU from sun
 0.53 x radius of Earth
 0.11 x mass of Earth
 Looks almost Earth-like
 Giant volcanoes, a huge canyon, polar caps…etc.
 Water flowed in the distant past, could have been life?
Jupiter:
 5.2 AU from sun
 11.2 x radius of Earth
 318 x mass of Earth
 Much farther from Sun than inner planets
 Most H/He; no solid surface (all gas)
 300 times more massive than Earth
 Many moons
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o Io: Active volcanoes al over
o Europa: possible subsurface ocean
o Ganymede: Largest moon in solar system
o Calisto: a large, cratered ice ball
 Jupiter has rings
Saturn:
 9.5 AU from sun
 9.4 x radius of Earth
 95.2 x mass of Earth
 Giant and gaseous like Jupiter
 Spectacular rings made of ices and rocks
 Many moons, including cloudy Titan
 Cassini spacecraft currently studying it
Uranus:
 19.2 AU from Sun
 4 x radius of Earth
 14.5 x mass of Earth
 Smaller than Jupiter, Saturn; much larger than Earth
 Made of H/He gas & hydrogen compounds
 Extreme axis tilt
 Moons and rings
Neptune:
 30.1 AU from sun
 3.9 x radius of Earth
 17.1 x mass of Earth
 Similar to Uranus (except axis tilt)
 Many moons including Triton
 Has rings
Pluto:
 39.5 AU from sun
 0.18 x radius of Earth
 0.0022 x mass of Earth
 Much smaller than other planets: dwarf planet
 Icy, comet-like composition
 Its moon Charon is smaller in size
 The plane of its orbit is tilted other dwarf planets: Eris, Ceres
Small Bodies in the solar system:
 Small bodies, the leftover scraps from the formation of the Solar System,
fall into three distinct groups:
o 1. Asteroids
 Rocky or metallic in composition
 Most are located between the orbits of Mars and Jupiter
o 2. Kuiper belt comets
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 Made mostly of ice
 Orbit the Sun beyond Neptune
 Orbit in same direction and plane as the planets
o 3. Oort cloud comets
 Mode mostly of ice
 Orbit at the out fringe of the Solar System
 Spherically distributed about the Sun
Properties of Asteroids:
 Small in size
 Not spherical
 All the asteroids in the solar system wouldn’t even add up to a small
terrestrial planet
 Meteor – a trail of light cause by a particle which enters Earth’s atmosphere
o Most particles are the size of a pea
o Completely burn up in Earth’s atmosphere
 Meteorite – a rock which is large enough to have survived its fall to Earth
o Cause a brighter meteor, sometimes called a fireball
o Have higher metal content than terrestrial rocks
o Contain Iridium and other isotopes not found in terrestrial rocks
Comets:
 Icy
 Not confined to the ecliptic and disappear after several weeks
 Most comets remain perpetually frozen in the outer solar system
 Only comets that enter the inner solar system grow tails
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Solar Systems History
Solar Nebula Theory – a theory of formation of the solar system consistent with our current observations
that supposes a rotating cloud of gas and dust gravitationally collapsed and flattened into a disk around
the forming Sun at the centre, from which the planets were formed


Describes formulation of solar system from nebula cloud made from dust and gas
Sun, planets, moons, and asteroids formed around same time 4.5 B years ago from nebula
Asteroid – small, rocky world; most asteroids orbit between Mars and Jupiter in the asteroid belt

Minor planets inside solar system
Comet – one of the small, icy bodies that orbit the Sun and produce tails of gas and dust when they
approach the Sun b/c it heats up so outgasses

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Effect of solar radiation and solar wind
First discovery by Edward Emerson
Comets leave trail of debris which leads to meteor showers on Earth
Formed by material left over from formation of planets
The entire solar system was created by collapse of lots of cloud, gas, and dust
Volatile – easily evaporated
Terrestrial Planets – small, dense, rocky worlds with little or no atmosphere


Inner planets closest to the Sun
E.g. Mercury, Earth, Venus, Mars
Jovian Planets – large, low-density worlds with thick atmospheres and liquid or ice interiors

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“Gas giants”
Jupiter, Saturn, Uranus, Neptune
Outer planets of solar system
Kuiper Belt – the collection of icy objects orbiting in a region from just beyond Neptune out to 50 AU+
Oort Cloud – the hypothetical source of comets, a swarm of icy bodies understood to lie in a spherical
shell extending to 100,000 AU from the Sun
Meteor – a small bit of matter heated by friction to incandescent vapour as it falls into Earth’s
atmosphere
Meteoroid – a meteor in space before it enters Earth’s atmosphere
Meteorite – a meteor that survives its passage through the atmosphere and strikes the ground
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Carbonaceous Chondrite – stony meteorite that contains small glassy spheres called chondrules and
volatiles; these chondrites may by the least-altered remains of the solar nebula still present in the solar
system
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Class of chondritic meteorites of 8 known and unknown groups of meteorites
Modified due to melting or differentiation from parent body
Formed when dust and small grains present in early solar system accreted to form primitive
asteroids
Meteor Shower – a display of meteors that appear to come from one point in the sky, understood to be
cometary debris
Half-Life – the time required for half of the radioactive atoms in a sample to decay
Uncompressed Density – the density a planet would have if its gravity did not compress it
Ice Line – boundary beyond which water vapour could freeze to form ice
Condensation Sequence – the sequence in which different materials condense from the solar nebula
depending on distance from the Sun
Planetesimal – one of the small bodies that formed from the solar nebula and eventually grew into
protoplanets
Condensation – the growth of a particle by addition of material from surrounding gas, atom by atom
Accretion – the sticking together of solid particles to produce a larger particle
Protoplanet – massive object, destined to become a planet, resulting from the coalescence of
planetesimals in the solar nebula
Gravitational Collapse – the process by which a forming body such as a planet gravitationally captures
gas rapidly from the surrounding nebula
Differentiation – the separation of planetary material inside a planet according to density
Outgassing – the release of gases from a planet’s interior
Heavy bombardment - the intense cratering that occurred sometime during the first 0.5 billion years in
the history of the solar system
NEO (near-Earth object) – a small solar system body (asteroid or comet) with an orbit near enough to
Earth that it poses some threat of eventual collision
Evolutionary Theory – an explanation of a phenomenon involving slow, steady processes of the sort
seen happening in the present day
Catastrophic Theory – an explanation of a phenomenon involving special, sudden events
Heat of Formation- the heat released by infalling matter during the formation of a planetary body
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Debris Disk – a disk of dust found by infrared observations around some stars

The dust is debris from collisions among asteroids, comets and Kuiper belt objects
Extrasolar Planet – a planet orbiting a star other than the Sun
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Chapter 2: Guide to the Sky: Patterns and Cycles
Constellations – one of the stellar patterns identified by name, usually of mythological gods, people,
animals, or objects

Most constellations are made up of stars that are not physically close to one another

Some stars may be moving in different directions
Asterism – a named grouping of stars that is not one of the recognized constellations
Magnitude Scale – the astronomical brightness scale; the larger the number, the fainter the star
Apparent Visual Magnitude – a measure of the brightness of a star as seen by human eyes on Earth
Flux – a measure of the flow of energy out of a surface; usually applied to light
Celestial Sphere – an imaginary sphere of very large radius surrounding Earth to which the planets, stars,
Sun, and Moon seem to be attached
Scientific Model – a concept that helps you think about some aspect of nature without necessarily being
true
Precession – the slow change in orientation of the Earth’s axis of rotation
- one cycle takes nearly 26,000 years
Zenith – marks the top of the sky above your head
Nadir – marks the bottom of the sky directly under your feet
You can measure distances on the sky as angular distances in degrees, minutes of arc, and seconds of
arc. An arc minute is 1/60th of a degree and an arc second is 1/60th of a minute. The angular diameter
of an object is the angular distance from one edge to the other.
North Celestial Pole – located directly above Earth’s North Pole
Rotation – motion around an axis passing through the rotating body
Revolution – orbital motion about a point located outside the orbiting body
Ecliptic – the apparent path of the Sun around the sky
Event
Vernal equinox
Summer solstice
Autumnal equinox
Winter solstice
Date
March 20
June 22
September 22
December 22
Season
Spring begins
Summer begins
Autumn begins
Winter begins
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Perihelion – Earth’s closest point to the Sun
Aphelion – Earth’s most distant point from the Sun
The Moon always keeps the same side facing Earth; you never see the far side of the Moon.
Solar Eclipse – the event that occurs when the Moon passes directly between Earth and the Sun, blocking
you view of the Sun
Umbra – the region of a shadow that is totally shaded
Penumbra – the portion of a shadow that is only partially shaded
Annular Eclipse – a solar eclipse in which the solar photosphere appears around the edge of the Moon in
a bright ring, or annulus; features of the solar atmosphere cannot be seen during an annual eclipse
Lunar Eclipse – the darkening of the Moon when it moves through Earth’s shadow
Saros Cycle – an 18-year, 11.33 day period after which the pattern of lunar and solar eclipses repeats
Timekeeping
Declination – the angular distance of an object on the celestial sphere measured north (+) or south (-)
from the celestial equator
Right Ascension – the angular east-west distance of an object on the celestial sphere measured from the
vertical equinox; measured in hours, minutes, and seconds rather than angular degrees
Solar Day – the average time between successive crossings of the Sun on the local meridian (24 hours)
Sidereal Day – the time between successive crossings of any star on the local meridian (23 hours, 56
minutes, 4.09 seconds)
Synodic Month – the time for a complete cycle of lunar phases (about 29.5 days)
Sidereal Month – the time for the Moon to orbit Earth once relative to any star (about 27.3 days)
Sidereal Year – the time for Earth to complete one full orbit around the Sun relative to any star
Tropical Year (Solar Year) – the time between successive spring equinoxes
Apparent Solar Time – time measured by the location of the Sun in the local sky such that noon is when
the Sun crosses the meridian
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Chapter 3: The Origin of Modern Astronomy
First Principle – something that seems obviously true and needs no further examination
Geocentric Universe – a model of the universe with Earth at the centre


Describes other objects from Earth’s point of view
Geocentric model is also known as Ptolemaic system - explains how planets, the Sun, and stars
orbit around Earth
Uniform Circular Motion – combinations of circles turning at uniform rates
Parallax – the apparent motion of an object because of the motion of the observer
Heliocentric Universe – a model of the universe with the Sun at the centre
Paradigm – a commonly accepted set of scientific ideas and assumptions
Ellipse – a closed curve around two points, called the foci, such that the total distance from one focus to
the curve and back to the other focus remains constant
Semi-Major Axis – half of the longest diameter of an ellipse
Eccentricity – a number between 1 and 0 that describes the shape of an ellipse (how elongated it is)
- the distance from one focus the centre of the ellipse divided by the semi-major axis
Empirical – description of a phenomenon based only on observations without explaining why it occurs
Hypothesis – a conjecture, subject to further tests, that accounts for a set of facts
Theory – a system of assumptions and principles applicable to a wide range of phenomena that has been
repeatedly verified
Natural Law – a theory that has been so well confirmed that it is almost universally accepted as correct
Speed – the rate at which an object moves
- total distance moved divided by the total time taken to move that distance
Velocity – both the speed and direction of travel of an object
Acceleration – the rate of change of velocity with time
Mass – a measure of the amount of matter making up an object
Weight – the force that gravity exerts on an object
Inverse Square Relation – a rule that the strength of an effect (such as gravity) decreases in proportion
as the distance squared increases
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Spring Tide – ocean tide of large range that occurs at full and new Moon
Neap Tide – ocean tide of small range occurring at first and third-quarter moon
Circular Velocity – the velocity needed to stay in a circular orbit
Closed Orbits – return the orbiting object to its starting point
Escape Velocity – the velocity needed to leave a body; will enter an open orbit
Open Orbit – does not return to Earth

An object orbiting Earth is actually falling (being accelerated) towards earth’s center
o
An object in a stable orbit continuously misses the earth because of its orbital velocity
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Chapter 4: Astronomical Telescope and Instruments
Electromagnetic Radiation – changing electric and magnetic fields that travel through space and transfer
energy from one place to another; ex. Light and radio waves

Radiation including visible light, gamma rays, X rays, and radio waves where electric and
magnetic fields vary together
Wavelength (λ) – the distance between successive peaks or troughs of a wave, usually represented by a
lowercase Greek lambda
Nanometre (nm) – a unit of distance equalling one-billionth of a metre, commonly used to measure the
wavelength of light
Angstrom (Å) – a unit of distance commonly used to measure the wavelength of light
Infrared (IR) – the portion of the electromagnetic spectrum with wavelengths longer than red light,
ranging from 700nm to about 1mm, between visible light and radio waves
Ultraviolet (UV) – the portion of the electromagnetic spectrum with wavelengths shorter than violet
light, between visible light and X-rays
X-rays – electromagnetic waves with wavelengths shorter than ultraviolet light
Gamma Rays – the shortest-wavelength electromagnetic waves
Photon – a quantum of electromagnetic energy that carries an amount of energy that increases
proportionally with its frequency but decreases proportionally with its wavelength
Atmospheric Window – wavelength region in which our atmosphere is transparent – at visual, radio, and
some infrared wavelengths
Refracting Telescope – a telescope that forms images by bending (refracting) light with a lens
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Reflecting Telescope – a telescope that forms images by reflecting light with a mirror
Primary Lens – in a refracting telescope , the largest lens
Primary Mirror – in a reflecting telescope, the largest mirror
Eyepiece – a short-focal-length lens used to enlarge the image in a telescope; the lens nearest the eye
Focal Length – the focal length of a lens or mirror is the distance from the lens or mirror to the point
where it focuses parallel rays of light
Chromatic Aberration – a distortion found in refracting telescopes because lenses focus different
colours at slightly different distances; images are consequently surrounded by colour fringes
Optical Telescope – telescope that gathers visible light
Radio Telescope – telescope that gathers radio radiation
Light-Gathering Power – the ability of a telescope to collect light; proportion to the area of the
telescope’s objective lens or mirror
Resolving Power – the ability of a telescope to reveal fine detail

Depends on the diameter of the telescope objective
Diffraction Fringe – blurred fringe surrounding any image, caused by the wave properties of light

Because of this, no image detail smaller than the fringe can be seen
Interferometer – separated telescopes combined to produce a virtual telescope with the resolution of a
much larger-diameter telescope
Adaptive Optics – a computer-controlled optical system in an astronomical telescope used to partially
correct for seeing


Improves performance of optical systems by reducing effect of wavefront distortions
Corrects deformations of incoming wavefront by deforming mirror to compensate for distortion
Magnifying Power – the ability of a telescope to make an image larger
Light Pollution – the illumination of the night sky by waste light from cities and outdoor lighting, which
prevents the observation of faint objects
Sidereal Tracking – the continuous movement of a telescope to keep it pointed at a star as Earth rotates
Photographic Plate – the first image recording device used with telescopes

records the brightness of objects, but with only moderate precision
Photometer – sensitive light meters to measure the brightness of individual objects very precisely
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Charge-Coupled Device (CDI) – an electronic device consisting of a large array of light sensitive
elements used to record very faint images
Array Detector – device for collecting and recording electromagnetic radiation using multiple individual
detectors arrayed on the surface of a chip
Digitized – converted to numerical data that can be read directly into a computer memory for later
analysis
False-Colour Image – a representation of graphical data with added or enhanced colour to reveal detail
Spectrograph – a device that separates light by wavelengths to produce a spectrum
Spectrum – a range of electromagnetic radiation spread into its component wavelengths (colours)
Grating – a piece of material in which numerous microscopic parallel lines are scribed

light encountering a grating is dispersed to form a spectrum
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Timekeeping
Timekeeping by Day
-Local meridian: Imaginary line ending at north and south celestial poles – cuts through our
zenith
-Solar Day: Average length of time between successive passes of the Sun across local meridian
 Time varies slightly throughout a year
-Determine length of day by measuring time it takes for any star to make successive passes across
local meridian called sidereal day
 Sidereal day = 23 hours, 56 minutes
 Shorter than solar day by 4 minutes b/c solar day the Earth travelled along orbit around
Sun and Earth needs more time to rotate before Sun crosses meridian
Timekeeping by Month
-Comes from the lunar phases’ cycle which is about 29.5 solar days (average month length) 
synodic month
 Synodic comes from Latin word “synod” – means meeting
 Meeting of the Sun and Moon at each new moon phase
-Use stars to measure length of lunar cycle – sidereal month – time is 27.3 days
 Shorter than synodic month b/c sidereal day is shorter than solar day
Timekeeping by Year
-Length of year related to time required for Earth to complete one full orbit around the Sun –
365.25 days
-2 different timeframes
 Sidereal Year: time taken for a complete orbit relative to the stars
 Tropical Year: time between successive spring (autumnal) equinoxes
-Sidereal year is longer than tropical year by 20 minutes – difference due to Earth’s rotation
-Solar Time used for timekeeping
-Apparent solar time determined by Sun’s position in the sky relative to local meridian
 Sun is right on meridian = noon
 Before Sun gets to meridian = ante meridian = before (morning)
 After Sun passes meridian = post meridian = after (afternoon)
-Each solar day differs from 24 hours b/c Earth’s orbit isn’t perfectly circular and b/c of Earth’s
23.5° tilt
-Average Solar Day: more important and used to keep track of time
 Adjusting clocks everyday
-Sandford Fleming proposed system of dividing Earth into 24 different time zones such that
within each time zone, time would be exactly the same
 Adopted universally by late 1800s
Calendars
-Tropical year (equinox to equinox) = 365.25 days
-365 days for one year = Egyptian concept  seasons drift through year by one day in every 4
years
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-Julius Caesar introduced idea that every 4 years an extra day would be added to account for this
discrepancy (leap years)
 Julian calendar
-Tropical year is 11 minutes short of 365.25 days
 Spring equinox moves backwards through calendar by 11 minutes each year
-1582: Pope Gregory XIII introduced slight variation in calendar = Gregorian calendar
 Set Spring equinox to March 21
 Adjusted leap day schedule so every century year (leap year) would be skipped as a leap
year unless it was divisible by 400
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Chapter 12: The Origin of the Solar System
Solar Nebula Theory – a theory of formation of the solar system consistent with our current observations
that supposes a rotating cloud of gas and dust gravitationally collapsed and flattened into a disk around
the forming Sun at the centre, from which the planets were formed


Describes formulation of solar system from nebula cloud made from dust and gas
Sun, planets, moons, and asteroids formed around same time 4.5 B years ago from nebula
Asteroid – small, rocky world; most asteroids orbit between Mars and Jupiter in the asteroid belt

Minor planets inside solar system
Comet – one of the small, icy bodies that orbit the Sun and produce tails of gas and dust when they
approach the Sun b/c it heats up so outgasses





Effect of solar radiation and solar wind
First discovery by Edward Emerson
Comets leave trail of debris which leads to meteor showers on Earth
Formed by material left over from formation of planets
The entire solar system was created by collapse of lots of cloud, gas, and dust
Volatile – easily evaporated
Terrestrial Planets – small, dense, rocky worlds with little or no atmosphere


Inner planets closest to the Sun
E.g. Mercury, Earth, Venus, Mars
Jovian Planets – large, low-density worlds with thick atmospheres and liquid or ice interiors



“Gas giants”
Jupiter, Saturn, Uranus, Neptune
Outer planets of solar system
Kuiper Belt – the collection of icy objects orbiting in a region from just beyond Neptune out to 50 AU+
Oort Cloud – the hypothetical source of comets, a swarm of icy bodies understood to lie in a spherical
shell extending to 100,000 AU from the Sun
Meteor – a small bit of matter heated by friction to incandescent vapour as it falls into Earth’s
atmosphere
Meteoroid – a meteor in space before it enters Earth’s atmosphere
Meteorite – a meteor that survives its passage through the atmosphere and strikes the ground
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Carbonaceous Chondrite – stony meteorite that contains small glassy spheres called chondrules and
volatiles; these chondrites may by the least-altered remains of the solar nebula still present in the solar
system



Class of chondritic meteorites of 8 known and unknown groups of meteorites
Modified due to melting or differentiation from parent body
Formed when dust and small grains present in early solar system accreted to form primitive
asteroids
Meteor Shower – a display of meteors that appear to come from one point in the sky, understood to be
cometary debris
Half-Life – the time required for half of the radioactive atoms in a sample to decay
Uncompressed Density – the density a planet would have if its gravity did not compress it
Ice Line – boundary beyond which water vapour could freeze to form ice
Condensation Sequence – the sequence in which different materials condense from the solar nebula
depending on distance from the Sun
Planetesimal – one of the small bodies that formed from the solar nebula and eventually grew into
protoplanets
Condensation – the growth of a particle by addition of material from surrounding gas, atom by atom
Accretion – the sticking together of solid particles to produce a larger particle
Protoplanet – massive object, destined to become a planet, resulting from the coalescence of
planetesimals in the solar nebula
Gravitational Collapse – the process by which a forming body such as a planet gravitationally captures
gas rapidly from the surrounding nebula
Differentiation – the separation of planetary material inside a planet according to density
Outgassing – the release of gases from a planet’s interior
Heavy bombardment - the intense cratering that occurred sometime during the first 0.5 billion years in
the history of the solar system
NEO (near-Earth object) – a small solar system body (asteroid or comet) with an orbit near enough to
Earth that it poses some threat of eventual collision
Evolutionary Theory – an explanation of a phenomenon involving slow, steady processes of the sort
seen happening in the present day
Catastrophic Theory – an explanation of a phenomenon involving special, sudden events
Heat of Formation- the heat released by infalling matter during the formation of a planetary body
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Debris Disk – a disk of dust found by infrared observations around some stars

The dust is debris from collisions among asteroids, comets and Kuiper belt objects
Extrasolar Planet – a planet orbiting a star other than the Sun
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Chapter 13: Comparative Planetology of the Terrestrial Planets
-Comparative Planetology – understanding planets by searching for and analyzing contrasts
and similarities among them

Branch of space science and planetary science

Natural processes and systems are studied by effects and phenomenons on different
bodies
-Mantle – the layer of dense rock and metal oxides that lies between the molten core and Earth’s
surface or a similar layer in another planet

Upper mantle = oxygen, magnesium, silicon, iron
o Common rocks = peridotite, olivine, garnets, pyroxenes

44.8% oxygen

21.5% silicon

22.8% magnesium

inner core is solid, outer is liquid, mantle is solid or plastic
-P Wave – a type of seismic wave involving compression and decompression of the material
through which is passes
-S Wave – a type of seismic wave involving lateral motion of the material through which it
passes
-Primary Atmosphere – a planet’s first atmosphere
-Secondary Atmosphere – a planet’s atmosphere that replaces the primary atmosphere

E.g. by outgassing, impact of volatile-bearing planetesimals, or biological activity
-Greenhouse Effect – the process by which a carbon dioxide atmosphere traps heat and raises
the temperature of a planetary surface
-Global Warming – the gradual increase in the surface temperature of Earth caused by human
modifications to Earth’s atmosphere
-Subduction Zone – a deep trench where one plate slides under another
-Rift Valley – forms where continental plates begin to pull apart
-Maria (Mare) – one of the lunar lowlands filled by successive flows of dark lava
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-Albedo – the ratio of the amount of light reflected from an object to the amount of light
received by the object

Equals 0 for perfectly black and 1 for perfectly white
-Ejecta – pulverized rock scattered by meteorite impacts on a planetary surface
-Anorthosite – aluminium and calcium-rich silicate rock found in the lunar highlands
-Breccia – rock composed of fragments of older rocks bonded together
-Large-Impact Hypothesis – hypothesis that the Moon formed from debris ejected during a
collision between Earth and a large planetesimal
-Magma Ocean – the exterior of the newborn Moon; a shell of molten rock hundreds of km
deep
-Multiringed Basin – large impact feature (crater) containing two or more concentric rims
formed by fracturing of the planetary crust
-Late Heavy Bombardment – the sudden temporary increase in the cratering rate in our solar
system that occurred about 4 billion years ago
-Micrometeorite – meteorite of microscopic size
-Runaway Greenhouse Effect – a greenhouse effect so dramatic that it amplifies itself,
becoming stronger with time
-Coronae – on Venus, large round geological faults in the crust caused by the intrusion of
magma below the crust
-Permafrost – permanently frozen soil
-Shield Volcano – wide, low-profile volcanic cone produced by highly liquid lava
-Outflow Channel – geological features on Mars and Earth caused by flows of vast amounts of
water released suddenly
-Valley Network – a system of dry drainage channels on Mars that resembles the beds of rivers
and tributary streams on Earth
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