Astronomy 2070
Sept 12 2009
Newtonian rules are the rules that govern the average persons world view.
however, they don’t extrapolate to outside the world to objects like the universe.
Quantum mechanics, the theory of general relativity, and the string theories are
used to TRY and explain how the universe operates.
zenith - the point directly above you
horizon - all points 90 degrees from the zenith
altitude - that angle of anything above the horizon
meridian - due north horizon =>zenith=>due south horizon
2*PIE*R/ 360 = D/0
Sept 15, 2009
Sumarians/Babylonians/Egyptians
Babylonians based their number system on groups of 60. some people think that
the Babylonians inherited this system from the Sumarians. b/c they used a base
60 we now have 360 degrees in a circle
they created the ideas of constellations and grouping stars. They created myths
to explain the motions of the objects in the sky.
they may have used constellations and their movement to keep time, for ag
purposes, and for religious purposes.
Greeks
400 - 150BC
Plato - (428-348BC) - believed that all natural motion is circular and that
reason is more important than observation.
Aristotle - painted the first theoretical picture of how the earth works. He
divided things into 5 categories - Earth, water, air, fire and quintessence (a
heavenly substance) The earliest physicist. believed that natural state of
things was to be at rest.
developed the roots of the scientific method
all properties if matter explained by their relation and place in the universe
believed that the earth was in the center of the universe and was stationary
and that heavenly bodies were perfect spears and in constant motion
Eratosthenes measured the circumference of the earth very accurately in
about 250BC.
Ptolemy - believed that the earth was at the center and therefore the sun
orbits the earth. and planets orbit on small circles whose centers orbit the
earth on larger circle (called epicycle). Also believed that the earth didn’t
have to be in the exact middle of the other planets orbit.
Copernicus/Keppler/Galileo
- 1520 - 1630CE
Copernicus - believed that Ptolemy’s model was wrong but he still believed
in circular motion
Sept 17 2009
Copernicus was one of the first people to believe that the earth was not the
centre of the universe and put the sun in the center of the universe. he
believed that the earth orbited just like any other planet. retrograde
movement when earth laps another planet.
George Le Maitre a catholic priest was one of the first people to articulate the
idea of the Big bang
Tycho Brahe - had the most accurate charts of the position of the planet
and his charts were accurate to w/i 4 min of arc. Greatest naked eye
observer
Keppler - a brilliant brilliant man, he is the greatest theorist of his day. he
believed that forces made the planets move. advocated Copernicus’ model of the
universe. Believed in the music of the spheres.
Galileo - first man to point a telescope at the sky. wanted to connect physics on
earth with the heavens. Dialogue Concerning the Two Chief World Systems
was his book. Galileo saw shadows cast by mountains on the moon and
realized that planets in space were like our planet - that is, not a perfect
sphere. He also was the first to record jupiters moons. Galileo observed
thee phases of Venus was the final evidence which buried the geocentric
model. he saw that there were gibbous and full phases which meant that
the sun had to be in center with Venus orbiting around it.
Giordano Bruno liked the idea of an infinite number of worlds. he believed
that no body could be called the center of the universe.
Sept 22 2009
Newton - born in 1642, the year Galileo died.
graduated from cambridge in 1665
he developed the binomial theorem , calculus, turned light into colours
returned to Cambridge as a lecturer in 1667 and also studied alchemy,
theology and biblical prophecy.
described as a jealous, egotistical, complex, and troubled. Absent- minded
and a confirmed bachelor
Newton changed the worlds view of physics. he believed that the universe was a
rational one that he likened to a clock. One must only wind up the clock and then
let it run. He didn’t believe that the universe was unrelated collection of activities,
but that it was a rational system.
Newton was a deist and that was how the universe was created
Newtons most important book The Principia Mathematica and in it he lays out
what we now call Newtonian physics. Newton asked the important question
“What causes things to move?” and from this was able to arrive at his
three laws.
speed - rate at which an object moves, the distance traveled per unit time
(m/s mi/hr)
velocity and objects speed in a certain direction MUST HAVE A DIRECTION
acceleration - a change in an objects velocity - a change in either speed or
direction is an acceleration
Forces
Forces change the straight line (translation) motion of objects
momentum - the (mass x velocity) of an object
force - anything that can cause a change in an object’s momentum
as long as the object’s mass does not change the force causes a change in
velocity or an acceleration.
Torques
torques change the rotation motion of objects
angular momentum - the (mass x velocity x radius) of an object
torque - anything that can cause a change in an object’s angular
momentum
As long as the object’s mass and or distribution of mass doesn’t change
(moment of inertia), the torque causes a change in angular velocity or an
angular acceleration
Newtons Laws of Motion
A body at rest or at rest at a constant speed along a straight line remains in
that state unless acted upon by a net external force. This is the Law of
Inertia
F=MA
For every applied force there is an equal but opposite force
Aristotle was wrong b/c his basic assumption was that an objects natural
state is at rest
The universal law of gravitation - b/w every two objects there is an
attractive force.
F=(G (M1 M2)/d^2)
Hubble, Lemaitre and Einstein and the Birth of modern Cosmology 19051931
Lemaitre was the first man to vocalize the term and the idea of the Big Bang. He
and Hubble convinced Einstein that the Universe was not static but in fact
expanding.
Sept 24, 2009
ecliptic - the plane of the earths orbit around the sun. Or from our point of
view it is the path of the sun through our sky. - the annual path of the sun
through the celestial sphere, which is a projection of the elliptical plane.
before Newton, scientists tried to explain the motion of celestial bodies as the act
of the gods or other heavenly objects. After Newton we describe the motion of
the planets through rigorous application of physics and mathematics.
there are officially 88 constellations. the constellations of the zodiac are
special b/c there are twelve, they are equated with a month and the sun
appears to move through each constellation throughout the year.
celestial equator - the extension of the earths equation to the celestial
sphere
North and South Celestial Poles - the points in the sky directly above the
Earth’s north and south pole.
ecliptic - the plane of the earths orbit around the sun
Sept 29, 2009
Lethbridge astronomy society visit Oct 17, nov 12, nov 18
Ch 1-4
the force that the earth exerts on me or you is equal to F=mg in place of
F=ma and a=g
acceleration of gravity - as objects fall they accelerate
the acceleration due to earths gravity is 10m/s^2 or g=10m/s^2
the higher the drop an object the greater its velocity will be at the bottoms
mass - the amount of matter in an object
weight - a measurement of the force which acts upon an object.
when you are in free-fall you are weightless. mass is constant but weight
changes with regards to the gravitational force that is acting on you
in the absence of a net torque the total angular momentum of a system
remains constant.
angular momentum - the momentum involved in spinning/circling = Mass x
Velocity x Radius
torque - anything that can cause a change in an objects angular momentum
(a twisting force)
Solar v Sidereal day
sidereal day - time it takes a star at the meridian to return to the meridian
(23 hrs 56 min 4 sec)
Solar day - time it takes the sun at Meridian (noon) to return to the meridian
(24 hrs
why the 4 min difference - as it rotates the earth orbits the sun (in the same
direction it is rotating) - the earth must rotate an extra degree (4 min) each
day to get back to the sun at meridian
it takes 27.3 days for the moon to make one complete orbit
this is called the sidereal month - it is the period of the moon’s orbit
with respect to distant stars.
the earth travels about 30 degrees around the sun a month so the
moon must orbit around the earth about 360 + 30 =390 degrees from new
moon to new moon
our calendar is based in the synodic month which is 29.5 days.
Oct 1 2009
tropical year v sidereal year
the period of the earths orbit around the sun defines the year - the sidereal year,
measured with respect to the distant stars, is the true orbital period of the
earth
our calendar year, based on seasons is
the tropical year, measured as the time b/w spring equinoxes
due to precession of the earth’s axis, the spring equinox changes its
position along the elliptical
apparent solar time - time based on the suns actual position in the local sky - told
by a sundial, noon occurs when the sun crosses the meridian
mean solar time is defined so that noon occurs at the time which the sun would
cross the meridian on average
mean and solar times agree only 4 times a year - mean time can be as
much as 17 min behind or 15 min ahead the sun.
Both solar and mean times are LOCAL times, different in each city. (time zones)
Kepler’s Laws
Each planet’s orbit around the sun is an ellipse, with the sun at one focus
a planet moves along its orbit w/ a speed that changes in such a way that a
line from the planet to the sun sweeps out equal areas in equal intervals of
time.
the ration of the cube of a planet’s average distance from the sun to the
square of its orbital period is the same for each planet.
a^3/p^2 = 1
a^3=p^2
Three basic kinds of nrg - we trade work for nrg. Energy is a really good idea :)
Kinetic - nrg of motion - ke = .5mv^2
potential - stored nrg - pe = mgh
radiative - nrg transported by light
Energy can be changed from one form to another.
what are nrg and mater
matter is material such as rocks, water, and air
energy - what makes matter move. energy is measured in many different
units. the metric unit of energy used by scientists is Joule
Oct, 8, 2009
standard time zones were introduced in the late 19th C. regions roughly 15
degreed in longitude share same mean solar time. standard time zones
to measure positions on the sky, we use a coordinating system which is a
projection of the earths coordinate system
Latitude --> Declination - measured in angles (degrees, arc-minutes
and arc-seconds)
Longitude --> Right Ascension - measured in time (hours, minutes,
and seconds)
Oct 13, 2009
Midterm Oct 22 - Ch 1-5 and 51 closed book but bring a cheat sheet 1, 8.5 by 11
on both sides. no calculators know aristotal and aristostanies, Kepler,
Copernicus. know the difference b/w a science and a pseudo-science keplers
laws and scientific notation
the location of the spring equinox is also the Prime Meridian (the sun is on
the ecliptic and the celestial equator at the same time). time is measured
eastward around the globe from the prime meridian every 15 degrees of
longitude is equal to 1 hour right ascension
mean solar time = the time on my watch
UTC = the time at Greenwich England
Local Sidereal Time (LST) = RA of some object on your meridian
RA of the Sun increases about 2 hours/month and the declination of the
sun varies between -23 degrees and 23 degrees.
Light - a vibration in an electromagnetic field through which energy is
transported. Light is dual natured with 2 characteristics
light as a wave
f(wavelength) = C
light as a particle E = hf H is Planks constant
light is the most important tool in Astronomy/Astrophysics.
the height of a wave is known as the amplitude and tells us about the
power of the wave. Frequency is the time it takes to complete one
wavelength.
frequency x wavelength = speed. (C)
a particle of light is called a photon
four ways in which light can interact with matter
emission - matter releases energy as light
absorption - matter takes energy from light
transmission - matter allows light to pass through it
reflection/scatter - matter directs light in another direction
light is made in atoms
Oct 15, 2009
Kirchoff’s Laws
A hot dense glowing object (solid or gas) emits a continuous
spectrum.
A hot, low density gas emits light of only certain wavelengths - an
emission line spectrum
When light having a continuous spectrum passes through a cool gas,
dark lines appear in the continuous spectrum - an absorption line spectrum
Hotter objects emit more total radiation per unit surface area
Stephan-Boltzmann law E=GT^4
Hotter object emit bluer photons (with a higher average energy)
Wien Law
wavelength max = 2.9x10^6/T
Oct 20 2009
Doppler effect
light emitted from an object moving towards you will have its
wavelength shortened
Called Blue Shift
light emitted from and object moving away from you will have its
wavelength lengthened
Red Shift
Light emitted from an object moving perpendicular to your line-ofsight will not change its wavelength.
Change in wavelength / wavelength = V/C - doppler effect formula
all planets orbit in the same direction around the sun and rotate in the same
direction that they orbit. moons and satellites orbit in the same direction around
their respective planets as the planets around the sun
MIDTERM COMES TO HERE !!!!!!!!!!!!!!!!!!!!
Oct 27, 2009
The Big Giant Cloud
a massive cloud greater than 50,000 ly across
it contains gas hydrogen and helium and fine dust
the cloud rotates and all the particles in the cloud are attracting each
other after a shock wave travels through the cloud.
as the particles collide both momentum and angular momentum must
be conserved. because of this the cloud will eventually turn from a sphere
into a disk.
Oct 29, 2009
large bodies in the Solar system have orderly motions
There are two types of planets
small rocky terrestrial planets
large hydrogen-rich Jovian planets
Asteroids and comets exist in certain regions of the Solar System
Nebular Theory - our solar system formed from a giant, swirling cloud of
gas a dust. the nebular theory holds that our solar system formed out of a
nebula which collapsed under its own gravity.
we observe stars in the process of forming today. stars are found within
interstellar clouds of gas.
elements and compounds condense out of the nebula depending on
temperature.
Nov 5, 2009
isotopes which are unstable are said to be radioactive
1st order exponential decay is represented by the formula Y = e^-x
an isotope spontaneously change in to another isotope in a process called
radioactive decay.
protons convert to neutrons
neutrons convert to protons
Planetary Geology Chapter 9
seismic waves - vibrations that travel through the earth’s interior that tell
us what earth is like on the inside
P waves go through the earths core but S waves don’t. thus we can
conclude that the earth’s core must have a liquid outer layer.
earths interior
core - highest density - made of nickel and iron
mantle - moderate density - silicone, oxygen, etc.
crust - lowest density - granite basalt, etc.
differentiation - gravity pulls high-density materials to center. Lower
density materials rise to surface and the materials end up separated by
density
radioactive decay is the most important aspect of planetary heating today.
planetary bodies cool off over time through convection, conduction, and
radiation.
smaller worlds cool off faster and harden earlier. Moon and Mercury are now
geologically dead as they have no internal heat.
larger objects have a smaller ration of surface area to volume and cool more
slowly
magnetic fields are crucial to our survival as they protect our planet from
solar winds. a solid core with a liquid mantel and heat are required to
create a magnetic field.
Nov 10, 2009
continents float on the lithosphere - it is made up of the crust and part of
the mantle
terrestrial planets all have the same basic construction
3/r -- this talks about the surface area vs the volume of a planet
surfaces are shaped by
impact craters - impacts by asteroids or comets
Volcanism - eruption of molten rock onto surface
tectonics - disruption of a planet’s surface by internal stresses
Erosion - Surface changes made by wind, water, or ice.
volcanism also releases gases into the planets atmosphere from the planets
mantle.
planets close to the sun are too hot for rain, snow or ice and thus have far
less erosion and are more difficult to maintain an atmosphere. Planets to
far from the sun are too cold for rain, limiting erosion. Planets with Liquid
water have the most erosion.
planets with slower rotation have less weather and less erosion and a weak
magnetic field.
density of craters tells you about the age of that area of the planet.
long cliffs on the planet Mercury indicate that it shrank early in its history.
there is a huge basin called the Caloris Basin on Mercury indicating such a
massive impact that we can see the evidence of it on the opposite side of
the Mercury.
Nov 12, 2009
conservation of angular momentum causes a ball’s apparent path on a spinning
platform to change direction
Coriolis effect on earth - air moving from pole to equator is going farther
from axis and begins to lag behind earths rotation.
air moving from the equator to the pole goes closer to the axis and moves
ahead of earth’s rotation.
Nov 17, 2009
effects of an Atmosphere
creates pressure that determines whether liquid water can exist on the
surface
absorbs and scatters light
creates wind, weather, and climate
interact with solar wind to create a magnetosphere
can make planetary surfaces warmer through greenhouse effect.
the earths atmosphere is about 10 km thick and is 80% nitrogen and 20% oxygen
and a bunch of trace gasses
pressure and density decrease with altitude b/c of the weight of overlying layers
is less
earths pressure at sea level is
1.03 kg/sq. meter
14.7 lbs/sq inch
1 bar
there is no clear upper boundary of our atmosphere.
most of the earth’s gas is less than 10 km from the surface but a small fraction
extends to over 100 km from the surface.
the earth’s atmosphere absorbs most types of light which is a good thing cause
we would be dead if it didn’t
only visible, radio, and certain IR and UV light makes it through to the
ground. to observe the other wavelengths we must put telescopes into
space
Atmosphere structure
Troposphere - lowest layer - temp drops with altitude. the atmosphere
is warmed by infrared light from the surface and convection.
Stratosphere - above the troposphere - temp rises with altitude in the
lower part and drop with altitude in the upper part. warmed by absorption
of UV sunlight
Thermosphere - about 100 km - temp rises with altitude. X-rays and UV
light from sun heat and ionize gasses
Exosphere - highest level with only trace amounts of atmosphere
atmosphere gradually fades into space. temp rises with altitude; atoms can
escape into space. warmed by X-ray and UV light
Light’s effect on the Atmosphere
Ionization - removal of an electron
Dissociation - destruction of a molecule
Scattering - the atmosphere causes a change in a photon’s direction
Absorption - a photons’ energy is absorbed by the atmosphere
X-rays and UV light can ionize and dissociate molecules. Molecules tend to
scatter blue light more than red. Molecules can absorb infrared light.
the earth is the only planet with a stratosphere b/c of UV absorbing ozone
molecules. those molecules protect us from the Sun’s UV light
- visible light passes through the atmosphere and warms the planets surface but
then the atmosphere absorbs infrared light radiating out from the surface and
traps it it in the atmosphere
greenhouse gasses listed as least powerful to most powerful from top to
bottom.
water vapor
carbon dioxide
methane
nitrous oxide
if there were no greenhouse effect here on earth the avg temp would be
about -16 degrees centigrade.
venus would be 510 degrees colder and earth about 31 degrees colder b/c of the
greenhouse effect.
the sky is blue b/c the atmosphere scatters blue light from the sun making it
appear to come from different directions and be all around us. Sunsets are red
b/c red light scatters less
the magnetic field around earth’s atmosphere protects us from charged particles
streaming off the sun (solar winds)
the magnetic field protects the atmosphere by stopping particles from the
sun hitting particles of our atmosphere and accelerating them past the
escape velocity. if it wasn’t for the magnetic field deflecting these particle
around us our atmosphere would be swept away from the earth.
Charged particles can enter the atmosphere at the magnetic poles, causing
an aurora
The most common speed for atoms in the atmosphere is the peak thermal
velocity. Although most atoms don’t have escape velocity a small fraction
of the atoms can and do escape permanently into space.
global wind patterns - global winds blow in distinctive patterns
equatorial - E to W
Mid-latitudes - W to E
high-latitudes - E to W
if the earth didn’t spin there would be two massive cells and air would
move out from the equator and down/up from the poles.
conservation of angular momentum causes a balls apparent path on a
spinning platforms to change directions
the coriolis effect deflects north-south winds into east-west winds. it also
causes large storm swirls in the North counterclockwise and in the south
clockwise
The Gaia hypothesis - states that the temp of the earth and the composition of
the earth’s surface are actively controlled by life on the planet. It suggests that if
changes in the gas composition, temp or oxidation state of the earth are caused
by extraterrestrial, biological, geographical or other disturbances, life responds to
these changes by modifying the abiotic environment through growth and
metabolism. in simple terms biological responses tend to regulate the state
of the earth’s environment in their favor.
Nov 19, 2009
the climate of a planet can change through
solar brightening - the sun very gradually grows brighter with time
increasing the amount of sunlight warming the earth.
Axis tilt - if a planet tilts towards the sun the area directed at the sun
will grow warmer
albedo change
sensitive measurements show that the moon and mercury have extremely thin
atmospheres. they are made up from gas ejected from impacts that eject surface
atoms
the ellipticity of Mars’s orbit makes seasons more extreme in the southern
hemisphere
Carbon Dioxide ice of polar cap sublimates as summer approaches and
condenses on the opposite pole. the residual ice of the polar cap during
the summer is primarily water ice
seasonal winds can drive dust storms on Mars. Dust in the atmosphere absorbs
blue light, sometimes making the sky look brownish-pink
calculations suggest Mar’s axis tilts range is from 0 to 60 degrees over
long periods of time. such extreme variations cause dramatic climate
changes and these changes can produce alternating layers of ice and dust
Somehow mars most most of its atmosphere and there was no longer any
greenhouse gasses to keep the planet warm. Its atmosphere was stripped
most likely because Mars lost its magnetic field after its interior cooled
Venus has a very thick carbon dioxide atmosphere with a surface pressure
90 times earth’s. Venus’s slow rotation produces a very weak Coriolis
effect
there is an extremely strong greenhouse effect on Venus. The clouds of venus
are very reflective and contain drops of sulphuric acid which also adds to the
greenhouse effect.
for reasons unknown reasons the upper atmosphere of Venus has very fast
winds
the earth retained it’s water in liquid form as the temp remained cool
enough. oceans dissolve atmospheric CO2 enabling carbon to be trapped
in rock
changes in the earths’s axis tilt might lead to ice ages. widespread ice tends to
lower global temp by increasing reflectivity
CO2 from outgassing will build up if oceans are frozen, ultimately raising global
temps again
earths avg temp has increased by .5 degrees in the past 50 years,
concentrations of CO2 are rising rapidly. an unchecked rise in greenhouse
gasses will eventually lead to global warming
antarctic air bubbles indicate that current CO2 concentrations is the highest in at
least 500000 years and most of that increase has happened in the last 50 years
Nov 24, 2009
Jupiter has over 60 moons
Saturn’s rings are made up of numerous, tiny individual particles
all four jovian planets have ring systems but Saturn’s are the only ones
that can be easily seen
Dec 8, 2009
the smallest angle which can be seen is calculated by the formula
= 2.5 x 10^5 (wavelength)/Diameter - wavelength and diameter must
have the same units (if both are in nanometer the answer comes out in arc
seconds)
the larger the diameter the smaller the area it can focus in on
the second important part of a telescopes properties is the light collecting
area
its area is A=pie(D/2)^2
Earths atmosphere causes problems for astronomers on the ground.
Bad weather makes it impossible to observe the night sky.
Air turbulence in the atmosphere distorts light and that is why stars appear
to “twinkle”
angular resolution is degraded by turbulence as well
man made light is reflected by the atmosphere, thus making the night sky
bright
Radio telescopes are huge because the wavelengths of radio waves are longer
than light wavelength
reflector telescopes use mirrors and refractors use lenses. professional
astronomers use reflectors exclusively
three kinds of refractors - Cassegrain focuses out the back. Newtonian
focuses out the side top. Coude - has a extra mirror and focuses out side
mid
telescopes can be used for imaging, timing or spectroscopy
it is possible to “de-twinkle” stars with adaptive optics which measure the
distortion in incoming wavelengths cause by the atmosphere and correct
them by changing the mirror’s shape.
X-Ray telescopes are different they use mirrors that are placed at very
shallow angles to the incoming photons. this is the only way x-rays can be
focused as they would pass through a mirror if the angle is too steep.
interferometry - two or more radio telescopes observe the same object. An
image is constructed with the angular resolution one would get from a dish
the size of the distance b/w the dishes. The light collecting area is still only
the sum of the areas of the individual dishes.
Asteroids are rocky left overs of planet formation
the largest is Ceres, diameter - 1000km
there are 150,000 asteroids in catalogs and probably over a million with a
diameter of less than 1 km
small asteroids are more common than large asteroids
all the asteroids in the solar system wouldn’t add up to even a small
terrestrial planet
some large asteroids have their own moon(s). The asteroid Ida has a tiny moon
named Dactyl
measuring orbits of asteroids moons tells us the asteroids mass
some asteroids are solid rock while others are just piles of ruble
Asteroids in a belt b/w Mars and Jupiter. The Trojan asteroids follow
Jupiter’s orbit 60 degrees behind and in front.
Lagrangian Points - mark positions where the combined gravitational pull
of the two large masses provides precisely the centripetal force required to
rotate with the.
the principle of least action is a simple way to calculate complicated gravitational
problems - in this case subtract the potential energy from the kinetic energy
the giant impact hypothesis suggests that an object named Theia formed at
L4 or L5 and crashed into the earth after its orbit destabilized, forming the
moon
the asteroids in the Kuiper belt are there b/c they are the ones that
survived. ASteroids in orbital resonance with Jupiter experience periodic
nudges. eventually those nudges kick all the asteroids except the ones in
the Kuiper belt out into the Oort cloud.
origin of the asteroid belt - rocky planetesimals b/w Mars and Jupiter didn’t
accrete into a planet b/c of Jupiter’s gravitation influence of orbital resonances.
meteorite - a rock from space that falls through the earths atmosphere..
there are two types. Primitive which are unchanged in composition since
they first frormed 4.6 billion years ago. and Processed which are younger,
and have experienced processes like volcanism and differentiation.
Meteor - the bright tail left by a meteorite.
Comets are formed beyond the frost line and are the icy counterparts to
asteroids. the nucleus of a comet is a dirty snowball. Comet tails result
from the comet melting/sublimating as it enters the inner solar system.
Coma is atmosphere that comes from the heated nucleus of a comet. the
plasma tail is gas escaping from the coma and is pushed directly away
from the sun by solar winds. the dust tail is pushed partly away from the
sun by photons from the sun
Oort cloud is a massive cloud of comets on random orbits extending to
about 50,000 AU
Kuiper belt a cloud of asteroids b/w mars and jupiter on orderly orbits from
30-100 AU in the disk of the solar system
Oort cloud comets were once close to the sun but they were kicked out by
the gravitational interactions with jovian planets.
It is difficult to classify Pluto as a planet as isn’t a gas giant like other outer
plantes. it has a very elliptical, inclined orbit and an icy composition more like
comets
There are many large icy bodies with similar quantities to Pluto out past neptune.
these large icy objects have orbits similar to the smaller objects in the Kuiper Belt
that become period comets
Tidal forces of the jovian planets or the sun can rip comets and asteroids apart
as they orbit through the inner solar system.
Fossil record shows hat occasional large dips in the diversity of Species;; mass
extinctions. most recent was 65 million years ago, ending the reign of the
dinosaurs.
iridium is very rare in earths surface rocks but is often found in meteorites.
there is a worldwide layer of iridium laid down about 65 million years ago,
probably by a meteorite impact. there are many dinosaur fossils below this
level but none above it.
a meteorite about 10 km in size would send large amounts of debris into the
atmosphere, blocking sunlight from reaching the surface. the resulting climate
change may have caused mass extinctions
Geologists believe they have found a large subsurface crater about 65
million years on in mexico
Asteroids and comets have hit earth in the past. A Major impact is only a matter
of time: it is a When not If question
Major mass extinction impacts are very very rare however, with only one in
millions of years
small impacts should happen almost daily
gravity of jovian planets (especially Jupiter) can redirect a comet out of the
Oort cloud towards earth.
While Jupiter has directed some comets towards earth, it has ejected many
many more out into the Oort Cloud
A sun like star is billions of times brighter than the sunlight reflected from its
planets
we can detect planets around a star in a number of different ways. Direct pictures or spectra of the planets themselves. Or Indirect - measurements
of stellar properties revealing the effects of orbiting planets.
Gravitational tugs - The Sun and Jupiter both orbit around their common
center of mass which is not the sun itself but very close to it.
the Sun therefore wobbles around that center of mass with the same period
as jupiter
The suns motions around solar system’s center of mass depends on tugs
from all the planets. Astronomers around other stars that measured the
motion of our sun could determine the masses and orbits of all the other
planets.
These movements in stars can be very difficult to detect and measure as they
can be as small as .001 arcseconds.
Measuring a stars doppler shift can tell us its motion towards and away
from us. current techniques can measure motions as small as 1 m/s
(walking speed!)
the first extra solar planet we discovered was a planet around star 51 Pegasi
which has a mass similar to jupiter’s but has a much much smaller orbital
distance.
Doppler shifts of star 51 indirectly reveal a planet with a 4- day orbital period.
short orbital periods mean small orbital distances
we cannot measure an exact mass for a planet w/o knowing the tilt of its
orbit, because doppler shift tells us only the velocity towards or away from
us. doppler data gives us lower limits on masses.
doppler data curves tell us about a planets mass and the shape of its orbit.
heavy planets will have higher frequency. faster orbiting ones will have
shorter wavelengths.
a transit is when a planet crosse in front of a star. the resulting eclipse
reduces the star’s apparent brightness and tells us the planets radius. we
don’t need to know the orbital tilt of a planet with this method and we can
accurately measure the planets mass.
the change in spectrum during a transit tells us about the composition of
the transiting planets atmosphere
special techniques can also eliminate light from brighter objects and thus we can
directly detect a planet
Gravitational lensing - mass bends light in a special way when a star with
planets passes in front of another star.
features in Dusk Disks gaps, waves or ripples in disks of dusty gas around
stars can indicate presence of planets.
most detected extrasolar planets have orbits smaller than jupiter as planets
at greater distances are harder to detect with the doppler technique
orbits of some extrasolar planets are much more eccentric than those in our solar
system
Most of the detected planets have a greater mass than jupiter.
some massive planets orbit very close to their stars “Hot Jupiter’s”
this is a problem as the nebular theory predicts that massive jupiter like planets
shouldn’t form inside the frost line
it is thought that a young planet’s motion can create waves in a planetforming disk and that matter in these waves can tug on a planet causing it
to migrate. close gravitational encounters n/w two massive planets can
eject one planet while flinging the other into a highly elliptical orbit.
Multiple close encounter with smaller planetesimals can also cause inward
migration of a jupiter like planet.
resonance b/w planets can also cause their orbits to become more eliptical
1 in 10 stars examined so far have turned out to have planets and others may
still have smaller (earth-sized) planets that we are unable to detect
Jovian Planets
Jupiter and Saturn are made up mostly of H and He Gas
Uranus and Neptune - mostly hydrogen compounds: water (H20), methane
(CH4), and ammonia (NH3) as well as some H, He a rock
Uranus and Neptune are denser than Saturn b/c then have less H/He
proportionately but they Uranus is less dense than jupiter and neptune,
although denser, isn’t much denser
adding mass to a jovian planet compresses the gas layers
greater compression is why Jupiter is not much larger than Saturn even
though it is three times its mass. there can be jovian planets with even
more mass than Jupiter and yet be smaller and there is greater
compression
Jovian planets aren’t quite spherical b/c of their rapid rotation
interior of Jovian planets
no solid surface
layers under high pressures and temps
Cores (10 earth masses) are made of hydrogen compound, metals,
and rock
the layers are different for the different planets
High pressures inside of Jupiter cause’s hydrogen to change phases with depth
Hydrogen acts like a metal at great depths b/c it’s electrons move freely
The core of Jupiter is thought to be made of rock, metals and hydrogen
compounds. the Core is about the same size as Earth but 10 times its mass
Jupiter radiates twice as much energy as it receives from the sun. the
energy probably comes from the slow contracting of the interior which
releases potential energy
models suggest cores of the jovian planets have similar compositions but
the lower pressures inside Uranus and Neptune means there is no metallic
hydrogen in their cores
Saturn also radiates twice as much energy it receives from the sun. That
energy probably comes from differentiation (helium rain)
neptune emits nearly twice as much energy as it receives, but the source of
that energy remains unknown
Hydrogen compounds in Jupiter’s atmosphere form clouds. Different cloud layers
correspond to freezing points of different hydrogen compounds
other jovian planets have cloud layers similar to Jupiter’s. Different compounds
make clouds different colours
On jupiter Ammonium sulfide clouds reflect red/brown. Ammonia, the highest
coldest layer, reflects white.
Methane gas of Neptune and Uranus absorb red alight but transmit blue lights.
blue light reflects off methane clouds making those planets look blue.
all of the Jovian planets have strong winds and storms
Jupiter’s strong magnetic field gives it an enormous magnetosphere.
Gasses escaping Io feed the donut-shaped Io torus.
all the Jovian planets have substantial magnetospheres but Jupiters is by far the
largest
Moons can be geological activity too
small moons less than 300 km have no geological activity
Medium sized moons 300-1500 km were geologically active in the past
Large Moons greater than 1500 km have ongoing geological activity
medium and large moons have enough self-gravity to be spherical. they
often have substantial amounts of ice.
medium and large moons are formed in orbit around jovian planets
they have circular orbits in the same direction as planet rotation
small moons are far more numerous than medium and large moons. they
don’t have enough gravity to be spherical and are often called “potatoshaped”
small moons can be captured asteroids or comets so their orbits often don’t
follow usual patterns
Io is the most geographically active body in the solar system. this is
because it is continually squeezed by jupiters massive gravitational force
as it orbits making its internal temp reach very high levels and resulting in
near continuous volcanic action
Tidal stresses also affect Europa’s ice surface. when the ice breaks the
water underneath quickly freezes. the water under the ice is kept from
freezing because of tidal heating caused by Jupiters gravitational pull
Ganymede is the largest moon in the solar system and has clear evidence of
geological activity, tidal heating and radio-active decay
Titan is the only moon in the solar system to have a thick atmosphere. it
consists mostly of nitrogen with some argon, methane and ethane
Titan’s surface is liquid methane and rocks made up of ice.
the other medium moons of Saturn almost all show evidence of past volcanism
and /or tectonics
rocky planets v icy moons
Rock melts at higher temps and only large rocky planets have enough
heat
Ice melts at lower temps and tidal heating can melt internal ice during
activity
Saturn’s rings are made up of numerous tiny individual particles that orbit
over saturns equator. the ring system is very thin
the tug of Saturn’s moons can cause small gaps within the rings
all four jovian planets have ring systems but only Saturn’s are easily visible. the
others have smaller, darker ring particles than saturn
Jovian planets have rings b/c the rings formed from dust created in
impacts on moons orbiting those planets. We know that the particle are to
small to be the leftover from planet formations. they are simply to small to
have survived this long. there must be continuous replacement of tiny
particles and the most likely source for them is from impacts with the
jovian moons
Jovian planets all have rings b/c they posses many small moons close in,
impacts on these moons are random.