ASTRONOMY
B.Miller
Contents
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

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History of Astronomy
Earth
Moon
Survey of Solar
System
Inner Planets
Outer Planets

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Asteroids, Meteors and
Comets
The Sun
Measuring Properties
of Stars
Stellar Evolution
Life in the Universe
HISTORY OF ASTRONOMY
HISTORY OF ASTRONOMY


Our picture of the universe has been assembled bit
by bit from many separate discoveries- from many
people, from many parts of the world
We divide the history of Western Astronomy into 4
main periods….
4 main periods of Western Astronomy

Prehistoric (before 500 B.C.)
 People
observed daily & seasonal motions of the sun, moon
and stars
 Learned cyclic motions for keeping time and determining
direction

Classical (500 B.C. – A.D. 1400)
 Began
to make measurements of heavens
 Constructed models to account for the motions of the
heavens using geometry

Renaissance (1400-1650)
 Reassessed
geometrical models, found problems
 Constructed new models
 Benefited from the development of telescope

Modern (1650 – Present)
Began research for physical laws (gravity)
 Huge technological advances (lenses, computers)
 Better math (Calculus)

Prehistoric Astronomy




Many of the astronomical phenomena well known to
ancient people, are not nearly as known to people
today.
We do not notice the heavens because of lights,
smog and changes in lifestyle
Structures like stonehenge were built around the
movements of the sun during each season
Why would it be important to understand when the
seasons would change?
The Celestial Sphere

We imagine this sphere as a gigantic dome that
stretches over head and all the way around the
Earth
 HORIZON-
the visual line where the sky meets the
ground

The celestial sphere “dome” is just a way to
visualize the heavens, therefore is just a model.
The stars are not really all contained in this
dome.
Constellations



We humans seek order in what we look at,
therefore ancient people noticed patterns and
forms in the night sky – CONSTELLATIONS
We see virtually the same constellations as ancient
people
The names given were probably mnemonic devices
to help people remember the seasons and help in
navigation.
Motions of the Sun & Stars

Daily or Diurnal Motion Stars
move across the sky from East to West just as our
sun seems to move
 This is why ancient people believed the Earth was not
moving and the celestial sphere moved around us
 2 points on the celestial sphere DO NOT move. These
are the North and South Celestial Poles
 Another useful sky marker is the Celestial Equator
 Both the celestial poles and celestial equator lie
directly above these same points on the Earth
Annual Motion



If you watch the sky over several months you would
notice new constellations appearing in the East and
some disappearing behind the Western horizon
This knowledge helped ancient people measure the
passage of time for each season “How many days
before we need to harvest the crops?” -for
example
We see this change in the constellations because of
our motion around the sun.
The Ecliptic

This is the path that the
sun takes across the
celestial sphere (or the
sky over head)
Seasons




Many people believe that we have seasons because
the Earth’s orbit is elliptical, however we
(N.Hemisphere) are nearest the sun in January when
the we experience winter ?????
THEREFORE the elliptical orbit IS NOT the reason
for the seasons
The tilt on our axis IS what causes the seasons
During part of our orbit around the sun the Northern
hemisphere is tilted slightly (23.5 degrees)
The seasons
Solstices and Equinoxes

Due to the tilt of the Earth on its axis, we see a
change in the position and path the sun appears to
take across the sky.
 Example:
In the northern hemisphere, in the summer the
sun rises in the northeast and sets in the northwest,
however in winter the sun rises in the southeast and sets
in the southwest

Astronomers give names to different positions of the
sun
 Spring
(Vernal) Equinox = near March 21
 Fall (Autumnal) Equinox = near Sept 23
 Summer Solstice = near June 21
 Winter Solstice = near Dec. 21


Spring begins and Autumn begins when the sun
crosses the celestial equator.
Days and Nights are of equal length during
Equinoxes

Summer solstice:
 Time
when the sun has reached its northern most
position in the sky
 Longest day of the year

Winter solstice:
 Time
when the sun has reached its southern most
position in the sky
 Shortest day of the year
Solstice’s sun positions


The sun’s rays are more direct during the summer
months, which warms the surface of the planet more
than the angular rays during the winter.
The changes in sun position were obvious to ancient
people, which can be seen in the buildings and
structures that orient along these astronomical
alignments
 Ex:
Egyptian temples & pyramids, Mayan pyramids, and
Stonehenge in England
The Planets & The Zodiac



Early cultures noticed objects in the sky that seemed
to move across the sky at regular intervals
These were planets, and they seemed to move
within a very narrow band in the celestial sphere.
This band is called the Zodiac.
Zodiac means “circle of animals” which is the circle
where the constellations are located
 Signs
of the Zodiac: Aries, Taurus, Gemini, Cancer, Leo,
Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius
and Pisces
Eclipses

Solar Eclipse:
 When
the moon passes
between the sun and
the earth

Lunar Eclipse:
 When
the Earth passes between the Sun and the Moon
Early Ideas of the Heavens:
Classical Astronomy

Greek astronomers were the 1st to try to explain the
workings of the heavens in a careful, systematic
manner, using observations & models
The Shape of the Earth

560-480 B.C. Pythagoras, a mathematician, was
teaching that the Earth was a sphere.
 Not
because he calculated it, but because he believed
a sphere was a perfect shape according to the Gods.

By 300 B.C. Aristotle was presenting arguments for
a spherical Earth through observations
 Viewing
Earth’s shadow during eclipses
 Observing that a traveler seemed to disappear into the
horizon as they got further away
The Size of Earth

Eratosthenese (276-195 B.C.)
 Made
the first measurements of Earth
 His estimate was a sphere with a circumference of
25,000 miles
 This
was amazingly close to today’s measurements!
Distance & Size of Sun & Moon


Before Eratosthenes, Aristarchus estimated the
relative sizes of Earth, Moon and Sun, and the
distances between them
He was not very accurate, but the ratios of distance
were not too far off
Motion of the Planets


The main thread of
astronomical research
for nearly 2,000 years
centered on the motion
of the planets
Early ideas of the Earth
being at the center with
all the planets and stars
moving around it.
Called the GEOCENTRIC
model by Eudoxus
Ptolemy



Unfortunately the Geocentric Model did not explain
“Retrograde motion”, which is the apparent
backward movement of some planets at some times
Ptolemy tried to explain why planets would briefly
change direction, then continue on their orbits
He proposed something called Epicycles, which is a
smaller circle in side of a larger orbit
Epicycles

There was a problem
with Ptolemy’s epicycle
theory
 For
an object to orbit
in a circle, they must
have something with
mass holding them in
that patter at the
center of the orbit,
therefore, support
failed.
Astronomy in the Renaissance

Copernicus (1473-1543)
 Could
not make sense of the geocentric model,
therefore investigated further on the Heliocentric model
 HELIOCENTRIC = “sun centered”
Planet
AU from Sun per
Copernicus
Actual Distance from Sun
Mercury
.38
.39
Venus
.72
.72
Earth
1.00
1.00
Mars
1.52
1.52
Jupiter
5.22
5.20
Saturn
9.17
9.54
Tycho & Kepler


Tycho was making some very accurate
measurements about the locations and paths of
planets
It was not until Kepler helped make mathematical
sense of Tycho’s notes that the idea of Elliptical
orbits emerged
 An
Ellipse is sort of oval in shape, with 2 foci at the
center.
Ellipse shape


This is the general
idea behind how an
ellipse gets his oval
shape.
We now know this is
the orbit shape of the
planets.
Kepler’s 3 Laws
I.
II.
III.
Planets move in elliptical orbits, with the sun at
one focus
Orbital speed varies so the line joining the sun
and the planet sweeps over equal area in equal
time intervals
The amount of time it takes to orbit the sun is
related to its orbit size
Galileo

Galileo Galilei (1564-1642) Italian scientist
 Was
not only interested in the motion of the heavenly
bodies, but of all objects
 He is often given credit for developing the telescope,
however a Dutch spectacle maker made it and Galileo
was the 1st to use it to look at the stars and planets
Galileo’s Contributions:





Saw mountains on the moon
Saw sunspots on the sun and noted their changes
Figured out that the sun rotated
Discovered the 1st 4 moons of Jupiter
Saw the rings of Saturn
 Galileo’s
finding & writings got him into trouble with the
church. He was vocal about his ideas of a sun-centered
universe. Because of his view he was placed under
house arrest for the rest of his life. He also went blind
from his extensive viewing of the sun.
Isaac Newton (1642-1727) &
The Birth of Astrophysics






Born the year Galileo died
Arguable the greatest scientist of all time
Made contributions in math, physics & astronomy
Invented Calculus
Determined a way to calculate the gravitational
force from the mass of an object
Invented milling of coins (process of putting grooves
in the coin edges to recognize if someone had dried
to shave gold from it)
Newton Continued…


Most of Newton’s findings are in the foundations of
Astronomy today
The math and physics that Newton applied to
solving questions in astronomy have developed into
a very logical term called ASTROPHYSICS.
EARTH
THE EARTH


Earth is a hug, rocky sphere spinning in space and
hurtling around the sun
Many other planets share similar properties, but not
in the right mix to allow for life.
Shape & Size of Earth


Radius of 6400 km (4000 miles)
Sphere shaped, with an equitorial bulge, which is
caused by gravity
 Objects
with a radius greater than 350 km will be
pulled into a sphere by gravity
 Objects with a radius less than 350 km will retain their
irregular shape



A sphere with a bulge is called an oblate spheroid
The bulge is caused from our rotation on the axis.
This spinning pushed outward against the force of
gravity
All points on the Earth take 1 day to rotate,
however, points closer to the equator move much
faster and go a greater distance.
Composition of Earth


Rock = minerals and chemical elements
Most common elements in surface rocks
 Oxygen
 Silicon
 Aluminum
 Magnesium
 Iron
 Olivine
(Much of Earth’s interior is composed of this
greenish iron-magnesium silicate)
Density of Earth

Density = mass/volume
Earth = 5.5 g/cubic cm (average density)

Comparison:

 Ordinary
rocks = 3 g/cubic cm
 Iron =8 g/cubic cm
 Water = 1 g/cubic cm
Earth’s Interior


We have only drilled 12 km of 6400 km total
radius of Earth
Most of what we know about Earth’s interior is
because of Earthquakes
 These
seismic waves are recorded around the world
 Tells us about which layers are liquid or solid
Seismic Waves
P-Waves


Pass through solids and
liquids
Pushes and pulls
matter by compressing
S- Waves



Only move through
solids
Moves up and down in
an S- like shape
Also occur on the
surface, and cause the
most damage
Differentiation

Causes the most dense materials to settle to the
center of a sphere and the lightest materials to
move to the outer surface.
Heating of Earth’s Core



As we move deeper into the Earth, the temperature
rises 2K for every 100 meters you descend.
At this rate the core would be 120,000K, however
much of this heat escapes from the surface.
Current estimates = 6,500K core temp (hotter than
the sun)
Why is the Core so Hot?


Pressure from Gravity
Radioactive elements in the core decay and release
energy
Age of Earth

The oldest rocks dated show Earth to be approx. 4
Billion years old
 If
we find older rocks then we would realize that Earth
is even older
Composition of Atmosphere



78% - Nitrogen
21% - Oxygen
~ 1% - Carbon Dioxide, Ozone, Water
Origin of the Atmosphere



Hypothesis #1 – The gasses of the atmosphere
were originally trapped in the Solid Earth
Hypothesis #2 – Other thought the gases were
brought here by past comets
Neither of these explain where all the Oxygen
came from ?????


The amount of Oxygen has steadily increased over
the past 3 billion years (according to rock contents)
Therefore, most scientists believe the Oxygen is
come from photosynthesizing algae and plants.
Origin of Earth’s Magnetic Field


It is generated by
electric currents
flowing in the molten
iron core.
The Earth’s geographic
poles do not coincide
with the magnetic
poles, this difference is
called the Angle of
Declination.
Magnetosphere


These magnetic forces create a zone around the
earth called the Magnetosphere.
It extends out 2-3 times the radii of the Earth
VanAllen Belts

The doughnut shaped rings caused by the
magnetosphere
Van Allen Belts


Energetic enough to penetrate spacecraft and can
be hazardous to space travelers
In places where these magnetic lines come close to
the surface, along with charged solar particles,
Auroras are formed.
Aurora Borealis
Motions of the Earth

Air and Ocean circulation: Coriolis Effect
 Ocean
and air currents sweeping across a spinning
planet like Earth are deflected from their original
direction of motion
 Also establishes direction of trade winds and jet stream
 Example:
round.
Tossing a ball back and forth across a merry-go-
Precession


The motion similar to the wobble that a top has
when it begins to slow down
26,000 year cycle
THE MOON
THE MOON

General Features:
¼
the size of Earth
 No air, water or life
 Covered in craters from past impacts
Moon-Surface Features

Craters
 Circular
pits, ranging from less than a centimeter to 240
kilometers

Maria
 Large,

smooth dark, areas
Highlands
 Bright
areas around the maria
 Composed of different rock types
Features cont.

Rays
 Long,
light streaks of pulverized rock that radiate from
some craters

Rilles
 Lunar
canyons
 Probably the result of ancient lava flows
Moon Craters
Moon Maria
Moon - Highlands
Moon - Rays
Moon - Rilles
Origin of Lunar Surface Features




Nearly all the features shown previously were
made by solid bodies impacting the surface
The scar is usually circular, unless it was a grazing
impact
The impact forces surrounding rock outward,
creating the ridge
In some cases the crater center rebounds creating a
central peak
Structure of the Moon

Crust & Interior
 We
can study the interior with seismic waves
 The interior has proven to be inactive
 The moon’s surface is covered in Regolith, meaning
“blanket” of shattered rock & fine powder (10’s of
meters thick)
 Below the Regolith layer is the Crust which is ~100km
(60 miles) thick.

The crust on the Earth’s side of the moon is thinner
than the other side.
 It
is thought that the Earth’s gravitational pull, pulled the
core closer to the surface on that side, leaving the crust
thinner

Beneath the crust is the thick Mantle 1000km thick
(600 miles).
 Moon’s

mantle does NOT move as Earth’s does
The moon’s core is small and contains far less iron
and nickel than Earth’s
Absence of a Lunar Atmosphere

2 Reasons for this:
 The
interior is too cool to cause volcanic activity
(therefore no gases are being released)
 The
moon is too small to have enough gravitational pull
to maintain the volcanic gases near the surface
Orbit & Motions of the Moon



The moons orbit is elliptical
The average distance from Earth is 380,000km
(250,000 miles)
Orbital period of 27.3 days
Moon’s Rotation



The same side of the moon always faces the Earth
The moon does turn on its axis, it is just the same
rate as its orbital period
This phenomenon is called Synchronous Rotation
Oddities of the Moon’s orbit

The moon’s orbit is tilted by ~5 degrees with
respect to Earth’s orbit around the sun
 This
is unlike the moons of Jupiter, Saturn and Uranus,
which all lie nearly exactly in their planets equitorial
planes

Our moon is also much larger, relative to the size of
Earth, than other moons are, relative to their planets
Odd orbital tilt of Moon
Therefore….


These things suggest that our moon formed
differently than other moons
But How?
Origin & History of the Moon


According to the newest hypothesis, the moon
formed from debris blasted out of the Earth by the
impact of a Mars-sized body
This event must have happened during Earth’s
formation
Moon formation illustration
Eclipses

An eclipse occurs when one astronomical body casts
a shadow on another
 Lunar
eclipses happen when the Earth’s shadow falls on
the moon
 Solar eclipses happen when the moon’s shadow falls on
the Earth
Appearance of Eclipses



During a Lunar eclipse, the Earth’s shadow
gradually spreads across the Moon’s face
It takes ~1 hour to completely cover the moon and
produce a total eclipse
At totality the moon appears almost dipped in
blood, and at some point disappears
Causes of Tides



The moon exerts gravitational pull on the Earth
This pull draws material toward the moon, in this
case ocean water is pulled in the direction of the
moon
The Differential Gravitational Force draws water in
the oceans into a tidal bulge on the side of the
Earth facing the moon.
Tidal Bulge
Moon Lore


Most stories about the moon are false
For example:
 Full
moons trigger anti-social behavior hence the term
“Lunatic”
 “Once in a Blue Moon” (the moon is never blue. This
refers to the second full moon in one month)
SURVEY OF THE SOLAR SYSTEM
SURVEY OF THE SOLAR SYSTEM
The Sun





Largest body in the solar system
More than 700 times the mass of ALL the other
bodies in the solar system
71% Hydrogen
27% Helium
With some carbon, iron, uranium
The Planets




Emit no light of their own
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus
and Neptune
Orbits are all nearly in the same plane like a
spinning pancake
The tilt of the axis is general perpendicular, except
for Venus and Uranus
 Uranus
has an extremely large tilt
 Venus spins backwards “retrograde rotation”
Inner Planets




Mercury, Venus, Earth,
Mars
Small, Rocky bodies
Thin to no atmospheres
“terrestrial” planets
Outer Planets




Jupiter, Saturn, Uranus,
Neptune
Gaseous, liquid or icy
No “true” surface
Called the Jovian
planets
Satellites (moons orbiting the planets)








Jupiter = 62
Saturn = 31
Uranus = 27
Neptune = 13
Mars = 2
Earth = 1
Mercury = 0
Venus = 0
Asteroids & Comets

Asteroids
 Far
smaller than planets (few meters to 1000km)
 Rocky bodies or metallic

Comets
 10km
(6 miles) or less in diameter
 Icy bodies


Most asteroids orbit the sun between the orbits of
Mars and Jupiter in the Asteroid Belt
Most comets orbit far beyond Pluto in a region
called the Oort Cloud. They rarely move into the
inner solar system
Origin of the Solar System

4 main observations we know about our solar
system
1.
2.
3.
4.
The solar system is flat, with all the planets orbiting in
the same direction
There are 2 types of planets, inner and outer, with
rocky ones near the sun, and the gaseous or liquid
ones farther out
The composition of the outer planets is similar to sun
All the bodies in the solar system whose ages have so
far been determined are less than 4.6 billion yrs. old
Solar Nebula Hypothesis

Proposed by Kant & LaPlace
 States
that the solar system originated from a rotating,
flattened disk of gas and dust, with the outer part
becoming the planets and the inner part becoming the
sun.
Other Planetary Systems



Astronomers have long searched for planets
orbiting stars other than our sun
These are called Extra-solar planets
They are very difficult to see because planets are
small and do not emit their own light
 However
years.
we have located many in the recent few
TERRESTRIAL PLANETS
The Inner Planets
THE TERRESTRIAL PLANETS

Diameters:
 Mercury
= 4,880 km
 Venus = 12,100 km
 Earth = 12,800 km
 Mars = 6,800 km

These 4 planets have completely different surfaces
and atmospheres
Mercury




Smallest terrestrial planet
Resembles our moon in both size and appearance
Mercury has many craters, the largest of which is
called Caloris Basin with a diameter of ~800 miles
Mercury’s surface shows old lava flows and
wrinkling as when a piece of fruit dries out.
Mercury’s Temperature & Atmosphere

One of the hottest surfaces in the solar system
 Equator

However at night it gets extremely cold
 -280

temp at noon = 800 degrees F
degrees F
This is a result of Mercury’s closeness to the sun, and
its slow rotation and lack of atmosphere
Mercury’s Interior

It is believed to have
an iron core beneath a
silicate crust
 Its
high density of 5.4
g/ cm3 a large iron
core with a thin crust.
Mercury’s Interior cont.


One possible explanation for the thin crust maybe
due to an enormous collision that may have blasted
off the crust layers.
It is unknown if any part of this iron core is liquid,
however based on its small diameter we may
presume that it is solid.
 This
would explain its low magnetic force
Mercury’s Rotation



It spins very slowly
Rotational period of 58 Earth days
Orbital period of 88 days
 Therefore,
Mercury spins exactly 3 times for each 2 trips
it makes around the sun

The time between sunrises on Mercury is 176 Earth
days. During this time the sun sometimes changes
direction across the sky
Venus


Of all the planets,
Venus is the most like
Earth in diameter and
mass
However it has
radically different
surfaces and
temperatures
The Venusian Atmosphere

Mainly carbon dioxide (96%)


Its clouds are sulfuric acid droplets





Measured from its spectrum and space probes
These clouds exist ~19 to 37 miles above the surface
No surface features can be seen
Dense clouds reflect the majority of light, making it
appear very bright
Atmosphere is extremely dense, exerting pressure ~100
times greater than Earth’s.
Surface temps of ~900 degrees F !!!
The Greenhouse Effect


The thick CO2 clouds creates a very strong
greenhouse effect on Venus
Venus has 300,000 times more CO2 than Earth
 This
makes Venus hotter than Mercury, even though
Mercury is closer to the sun!
The Surface of Venus (by Pioneer)





The surface is hidden under its thick clouds however
scientists have mapped ground features with radar
Less mountainous than Earth, with only 2 major
highland areas
Little to no evidence of plate tectonics
Some craters and mountains, lava flow domes
Evidence for active volcanoes
 Electrical
discharges detected, sulfur increases
Why does Venus have fewer surface
features than Earth?


Scientists believe the rocks contain more water
The intense temperatures break the crust down
faster
Interior of Venus


Probably similar to Earth with an iron core and rock
mantle
Scientists rely on deductions from its gravity and
density (similar to Earth)
Rotation of Venus

Venus spins on its axis more slowly than any other
planet in the solar system.
 243

days to complete one rotation!
It spins backward (retrograde rotation)
 Some
astronomers hypothesize this retrograde rotation
is due to Venus being struck shortly after its birth by a
large planetesimal (sun rises in the West)
 Its slow rotation causes Venus to have a very weak
magnetic field
Mars
Mars





Red in color – from iron minerals
Seems Earth-like, compared to Mercury and Venus
About ½ the diameter and mass of Earth
Equator temperatures reach 50 degrees F
Clear enough atmosphere for us to see the surface
very well
Mars’ Polar Ice Caps


These ice caps grow and shrink as they are tilted
toward and away from the sun (just like Earth’s ice
caps)
The top layer is made of frozen carbon dioxide,
however it is believed that regular frozen water lies
below.
Mars Ice Cap
Other Martian features


“viking” revealed very interesting dried up river
beds, leading scientists to believe that water once
flowed on Mars.
Evidence for water on ancient Mars:
 River
beds
 Islands that have water carved edges
 Canyons that appear eroded by moving water
Martian Atmosphere

Mostly Carbon Dioxide (95%)
 3%

Atmosphere density is very low
 1%

Nitrogen, traces of water and Oxygen
of the density of Earth’s
Very weak greenhouse effect
 This
inhibits Mars’ ability to hold on to heat
 Leads to cold temperatures
 Up to 50 degrees F at mid day at equator and -67
degrees F at night



Martian winds are typically gentle, with seasonal
gales near the poles
It never rains (there is too little water)
CO2 snow falls on the poles
What led to loss of all water?


Low gravitational forces allowed gases to escape
over the 1st 1-2 billion years of Mars’ history
Then Tectonic activity slowed, which reduced the
amount of new gases released to the surface.
Martian Interior




Scientists believe the interior of Mars is
differentiated like Earths with Crust, Mantle and
Core.
The interior is cooler than Earth’s
No evidence of large scale tectonic activity
Mars has probably entered planetary “old age”
Mars’ Interior
Martian Moons

Mars has 2 tiny moons, both are less than 20km
across
 Phobos,


Deimos
They are NOT spherical because they are too small
for gravity to shape them.
Phobos is cracked as though it was struck by a
larger object
Mars’ Moons

Phobos

Deimos
Kepler… again


Kepler thought that if Earth has 1 moon and Jupiter
had 4, then Mars must have 2 because it lies
between them !!!
It turned out that he was right about Mars’ 2 moons,
however for completely illogical reasons.
Life on Mars



Scientists have long wondered if living organisms
existed or originated on Mars.
The existence of past water (which is so important to
life) leads scientists to continue the search for ancient
life
At one point fossilized rod-shaped impressions were
found in some Martian rocks and asteroids – believed
to be bacteria fossils


However, it has since been discovered that some erosion
processes can form similar shapes
It will take further sampling to tell us for sure if life ever
existed on Mars.
THE OUTER PLANETS
The Gas Giants
THE OUTER PLANETS




Jupiter
Saturn
Uranus
Neptune
Jupiter’s Properties

The largest planet in the solar system in radius and
in mass
 10
X the diameter of Earth
 300 X the mass of Earth

Atmosphere consists of Hydrogen, Helium and
Hydrogen-rich gases
 Methane,
Ammonia, Water


Jupiter’s bright colors may come from complex
organic molecules with unknown composition
Jupiter rotates once every 10 hours, therefore it
bulges significantly at the equator
Jupiter’s Interior


We cannot see past the clouds, nor can we probe
the interior. Instead we rely on theory to tell us
what is inside
We calculated density by mass/volume determined
by gravitational pull
 =1.3
g/cm3 (slightly greater than water)

Deep within Jupiter, gravity presses gas into liquid.
 Forming
a sea of liquid nitrogen ~10,000 km below
the surface

Jupiter’s interior is extremely hot (3,000 K)
 This

is 5 times hotter than the core of the Earth
Jupiter emits huge amounts of heat, even more than
it receives from the sun.
 This
creates convection currents that move the surface
and atmosphere.
Jupiter’s Interior
Jupiter’s Atmosphere





Warm gas rises to the surface, cools then sinks
again.
Jet stream winds of 200 mph
The Great Red spot was discovered in the 17th
century, and is a permanent feature in Jupiter’s
atmosphere circulation
Jupiter also has Van Allen Belts and Lightening
Jupiter also experiences auroras resulting from its
strong magnetic field ~ 20X stronger than Earth’s.
Jupiter’s Ring
Jupiter’s Ring



In 1977, thin rings were detected around Uranus
and then 2 yrs later around Jupiter
Jupiter’s ring is made of tiny rocks
Particles in the rings are constantly being pulled
down toward Jupiter’s surface, therefore the ring
remains because particles are being added to the
ring at the same rate
Jupiter’s Moons

Jupiter has 62 moons!
 Most
not visible from Earth
 They were detected by “Voyager”

The Galileon satellites: (the largest)
 Io,

Europa, Ganymede & Callisto
Ganymede is larger than Mercury – making it the
largest moon in the solar system.
Io (pronounced “eye-oh”)



Nearest to Jupiter
It is under great gravitational force from Jupiter
Due to the forces, Io is volcanic with active sulfur
volcanos.
Europa





Smallest of the Galilean moons
Looks like a cracked egg
No craters, may be due to intense heat that has
reformed the surface
Shows ice flows (glaciering)
Some astronomers speculate an ocean on Europa
may harbor life, but no evidence exists to support
the idea
Europa
Ganymede & Callisto
Ganymede & Callisto



Both appear somewhat like our moon
Below the surface, however, they are very icy, and
may have a liquid water ocean below the surface
The rest of Jupiter’s moons are much smaller than
the Galilean moons
 They
are all pock marked
Saturn


2nd Largest planet in the solar system
10 AU from the sun
Saturn’s Properties





Diameter is 10X Earth’s
Mass is 95X that of Earth
Low density of 0.7 g/cm3
Composed mostly of hydrogen and other hydrogenrich compounds
Saturn radiates more energy than it gains from the
sun
 Indicates
an internal heat source
Saturn’s Interior

Frozen Ammonia gas obstructs the view of deeper
layers of its atmosphere
Saturn’s Rings





1st seen by Galileo
They are wide, but very thin
They extend from 30,000 to 136,000 km above
Saturn’s surface.
However, they are only a few hundred meters thick
The particles that make up the rings range from few
cm to a few meters in diameter



Composed mostly of ice and water
Some of the darker rings may contain carbon
compounds
The gaps in the rings probably arise from tiny
moons disrupting the ring materials
Origin of the Rings


Rings are somewhat short-lived
Without new gases and dust being added to the
rings, they would disappear in a few million years.
Saturn’s Moons


Saturn has several large moons and about 24
known smaller ones (~31 in total)
Most orbit in a flat plane, like a mini-solar system
Titan (Saturn’s famous moon)



Largest Saturn moon, with a diameter of ~3,000
miles (which is bigger than Mercury)
It has its own atmosphere, which is mostly Nitrogen
Some astronomers believe Titan’s surface is covered
with oceans of Liquid Methane or Hydrocarbon
Ethane
Uranus 
Uranus

Small compared to Jupiter and Saturn
 15


x the mass of Earth
~19 AU from the sun
Appears as a blue featureless disk from Earth
Uranus’ Structure

Rich in hydrogen, water and methane
 The



thick methane gives it its blue color
Extremely cold
Average density of 1.2 g/cm3
Fast rotation of 17 hours
Uranus’ rings and moons



Composed of meter sized particle
The rings are dark in color, implying that they are
made of carbon
Uranus has 5 large moons and ~20 small ones
Miranda – Moon of Uranus



The smallest of the 5
large moons
Totally unlike any
other body in the solar
system
It is cracked and looks
like patchwork as
though it broke apart
at one time.
Uranus’ Odd Tilt

The rotational axis is tipped so its equator is nearly
perpendicular to its orbit


This tilt gives Uranus an odd pattern of day and
night
It also causes the planet to be heated unevenly and
may explain the lack of cloud bands
NEPTUNE





Outermost of the large
planets
4 X the diameter of
Earth
Blue in color due to
methane
30 AU from the sun
Galileo noticed it in
1613, but it was not
tracked until 1846!
Neptune’s Structure


Similar to Uranus’ (mostly water, hydrogen and
Methane)
Density of 1.67 g/cm3
Neptune’s Atmosphere





Blue in color from Methane
Has distinct blue cloud bands and belts
Very fast winds of 1,300 mph
Rotates once every 16 hours
Photos have been taken in the past that showed a
large blue dot or storm, however recent photos
show no such cloud formation.
Neptune’s Rings & Moons



Has very narrow rings, containing more dust than
Saturn’s and Uranus’ rings
6 small moons orbiting close to Neptune, and 7
other moons at much greater distances
The huge moon “Triton” orbits backwards
 Its
size allows it enough gravity to hold onto gases,
giving it an atmosphere
 Its surface is wrinkled and covered with craters and
geysers that spew soot.
ASTEROIDS, METEORS, COMETS
Meteors, Asteroids & Comets
Meteors, Asteroids & Comets




Bodies much smaller than the planets
Inner solar system asteroids are rocky
Outer solar system Asteroids are icy
Highly studied because of their beauty, and
because they are potentially deadly
Meteors, Meteroids & Meteorites

Meteor “shooting
star” – streak of light that appears and
disappears in only fractions of a second
 The glowing visible trail

Meteoroid The
actual solid body that becomes heated by friction.
 This term is used to describe the body BEFORE it enters
Earth’s atmosphere
Heating of Meteoroids

The meteoroid collides with atmospheric molecules
and atoms
 Within
seconds the outer layer reaches thousands of
degrees K.
 Surface layers are vaporized and the trailing
evaporated matter emits light


Meteoroids bombard Earth continually, hundreds of
tons per day
If they do not completely vaporize, the fragments
are called Meteorites.
Atmosphere
Earth
Meteorite
Meteor
Meteoroid
Meteorites

Astronomers classify meteorites into 3 broad
categories
 Iron
 Stony
 Stony-Iron

(ha)
Some meteorites contain organic compounds,
including amino acids, the same complex molecules
used by living things to make proteins


The presence of amino acids indicates that the raw
materials of life can form in space and may have
been available right from the start with in the solar
system
Astronomers believe meteorites are fragments from
asteroids and comets
Asteroids


Small, generally rocky bodies that orbit the sun
Found throughout the solar system, but most lie in
the Asteroid Belt
 This

belt is between the orbits of Mars & Jupiter
Their numbers are great, but their combined mass is
small (1/1000 of Earth)
Asteroid Size and Shape



Difficult to measure because they are so small, they
only reflect light, and different compounds reflect
different amounts of light.
The smallest asteroids are only seen if they get very
close to Earth
Some asteroids are hardly solid at all, and are
basically a pile of rubble barely held together by
gravity
 This
gives them their irregular shape.
Asteroid Composition

When sunlight falls on an asteroid, the minerals in its
surface reflect a spectrum of light, telling us what it
is made of.
 Silicate
Rich – Inner belt region
 Carbon Rich – Outer belt region
Origin of Asteroids


Asteroids are probably fragments of planetesimals,
the bodies from which the planets were made
This band of debris has never formed into a planet
because the gravitational forces from Jupiter and
Mars pull material in different directions.
Danger posed by Asteroids

Because of the magnitude of danger posed from an
asteroid striking the Earth, we have several
international monitoring systems.
 LINEAR
= Lincoln Near Earth Asteroid Network
 British NEO = Near Earth Object

It is believed that we could deflect an incoming
asteroid with a nuclear bomb
Comets
Comets



Have long been held in fear and reverence
Their sudden appearance & disappearance after a
few days or weeks has added to their mystery
Seeing comets now is a rear treat, because today’s
light pollution makes viewing them difficult
Structure of Comets

Tail Narrow
column of dust and gas that may stretch across
the inner solar system up to 100 million Km.

Coma –
 Gas
cloud around the nucleus, can reach 100,000 Km
in diameter (10x the size of Earth)

Nucleus –
 Block
of ice and gases that have frozen into an
irregular mass, approx. diameter of 10 Km.
 Sometimes described as a “dirty snowball”
Comet Diagram
Coma:
~ 100,000 Km across
(60,000 miles)
Comet Nucleus
~ 1-10 km in
Diameter
Hydrogen Envelope
~10 million km across
(6 million miles)
Coma
Toward the Sun
Composition of Comets



Spectra of gas from the tail shows that comets are
rich in water, CO2 and CO and small amounts of
other gases
Evaporating water is broken up by UV radiation
into oxygen & hydrogen gas, this produces the
hydrogen gas cloud around a comet
If a comet passes by the sun too often it will either:
 Erode
away until it is gone OR
 Be pulled into the sun (dozens per year do this)
Formation of the Comets Tail

Radiation Pressure:
 Force
from sunlight striking tiny dust grains
 This is why a comets tail is always pointing away from
the sun.

Solar wind:
 Pushes
gases away from the sun, and magnetic fields
carried in the solar winds add to this tail formation and
direction
Light from the Comets Tail


The dust particles are reflecting some light from the
sun
Fluorescence
 Gases
emit light of their own. This light is produced
when light at one wavelength is converted to light at
another wavelength (A photon is given off as energy)
Giant Impacts



Every few thousand years, Earth is hit by a huge
meteoroid (10’s of meters or more in size
The energy released when these strike is HUGE!
Example:
A
meteoroid weighing 200 pounds, traveling at
30km/sec carries the kinetic energy of 100 tons of
dynamite!
 Or if 10m in diameter = 1 nuclear bomb
Yucatan Crater
Giant Meteor Craters

Many craters scar Earth’s surface
 One
famous one: Arizona Meteor Crater
 50,000
yrs. Old
 Estimated 50 meter diameter meteorite
 Left crater 1.2 km across, 200 m deep
 1908
a meteorite hit in Siberia causing great damage
 Scientists have uncovered evidence of many other
craters.
Siberia Meteorite - 1908

There were no
witnesses to this
destruction, however it
is believed that a
meteorite burst into a
fire ball just above the
ground, and
disintegrated before
impacting the ground
Arizona Meteor Crater
Mass Extinctions & Asteroid/ Comet
Impacts

65 million yrs. Ago an asteroid/comet hit the Earth
disrupting the atmosphere
 It
exterminated the dinosaurs and many species of
plants
Evidence for this Event




High amounts of iridium in the sediments (iridium is
common in Asteroids)
Layer of Soot
Layer of tiny quartz
Faint circular depression off the Yucatan region of
Mexico that is 65 million yrs. old
Thank You – Asteroid !



Not all living organisms went extinct
Rodents probably survived better than the reptiles
because they could regulate their body
temperatures
This even allowed our ancestors (the mammals) to
become the dominant classification on Earth!
THE SUN
THE SUN – Our Star
The Sun



Luminous ball of gas
More than 100 X the diameter of Earth
This “Nuclear Furnace” burns 600 million tons of
hydrogen into helium every second!
Size and Structure


The sun has enormous gravity and crushes material
in its interior
To offset this gravitational force, the sun must be
very hot
 Otherwise

it would collapse
The sun is always losing energy, therefore, it must
keep replacing energy to remain stable
Properties of the Sun




Distance from Earth = ~1 AU
Surface temp. = 5780 Kelvin (9900 F)
Core temp. = 15 million Kelvin (27 million F)
Composition
 71%
Hydrogen
 27% Helium
 2% Heavier elements
Sun Diagram
The Sun’s Properties



~150 million km (93 million miles) = 1 AU from
Earth
We find the sun’s temperature from its color
The sun is gaseous throughout because of its
extreme heat
Solar Interior


The layers become more dense as we look deeper
from the surface
The very surface that we see is called the
Photosphere
Energy Flow in the Sun




Energy flows from hot to cold, therefore we infer
that the core is hotter than the surface.
Near the core energy moves by radiation carried
by photons through the
Convection Zone – The area of rising and sinking
gases, just outside the radiative zone
Granulation – Narrow darker zones, that visually
indicate the direction of the confection currents
Powering the Sun

The sun generates its own energy by converting
hydrogen into helium by Nuclear Fusion
 Nuclear
Fusion bonds 2 or more nuclei into a single
heavier one
 During this reaction neutrinos are released and leave
the surface of the sun. These are of great interest to
scientists and have therefore developed elaborate
detection experiments.
Solar Magnetic Activity

Sunspots The
most common type of solar magnetic activity
 Dark regions
 Size range, few hundred km to a few thousand km
 Last for a few days to over a month
 They are cool spots, because they contain strong
magnetic fields
Solar Magnetic Fields


The magnetic fields in the sunspots are more than
1,000X stronger than Earth’s
Electrons are forced to follow the magnetic field
lines and spirals around and loops away from the
surface of the sun
Magnetic Field Loops

Field Loops
 Hot
gas rises away
and cools.

Photosphere
Prominences and Flares




Magnetic disturbances
Huge plumes of glowing
gas (100X the size of
Earth)
~160,000 km high
Increase radio wave and
x-ray emissions in a few
seconds

http://www.youtube.c
om/watch?v=lXmeGp
mrEVI
Solar Wind


Atoms from the sun streaming into space
Hydrogen and helium atoms are being released
from the sun constantly
 It

looses less than 1 ten-trillionth of its mass every year.
These atoms pick up speed as they get closer to
Earth and reach 500 km/sec at Earths orbit
Solar Cycle



Flare activity changes from year to year
The number of flares rises and falls every 11 years
Astronomers are studying this solar cycle to
determine its impact on climate
Sunspot cycle Graph

More sunspots means Greater solar activity and
greater magnetic activity
 So….
The lowest points on the graph would be the
times of lowest sun intensity…
Maunder Minimum

British astronomer found a period between 16451715 where sunspots were rare.
 This
coincides with a 70 yr. spell of abnormally cold
winters in Europe and North America
 Glaciers in Alps advanced
 Rivers froze early and remained frozen late
 The North Sea Froze
 Called the “Little Ice Age” by meteorologists
Solar Activity-Sea Temp Graph
MEASURING STAR PROPERTIES
MEASURING STAR PROPERTIES

Astronomers learn about the properties of stars by
using physical laws and theories
 Theories
of Light – tell us the starts surface temp.,
distance and motion
 Theories of atoms – tell us a starts composition

Astronomers may often use several methods to study
a single property of a star
Measuring Distance by Triangulation

Triangulation
 Construct
a triangle
with one side being
known, one is unknown.
Use trig to find the
unknown
Distance by Parallax

Parallax
 Change
in an objects apparent position caused by a
change in the observer’s position
 Using this method may require 6 months between
measurements.
 Ex:
When driving, a mailbox seems to move faster by than a
house, because of its distance
Temperature

An objects temperature can often be deduced from
the color of light emitted
 Not
far off from how you tell how hot a burner on an
electric stove may be.
Luminosity

Luminosity is the measure of energy a start radiates
each second.
 Ex:
Common example of luminosity
 100
watts = typical table lamp
 1500 watts = outdoor parking lot light
 4 X 1026 = The Sun
 Inverse
Square Law
 Relates
an objects luminosity to its distance and its
“apparent” brightness, which is how bright it looks to us.
The Magnitude System


Lower number indicates brighter stars
Each magnitude difference corresponds to a factor
of 2.512 (the 5th root of 100) in brightness.
Spectra of Stars


A stars spectrum depicts the energy it emits at each
wavelength
The following characteristics can be found:
 Composition
 Temperature
 Luminosity
 Velocity
in Space
 Rotational speed
Binary Stars



Stars that are held together by gravity and orbit
together as a pair
This relationship gives additional ways to measure
stellar mass
These stars are only a few AU apart, (some may
even touch eachother)
 Example:
Mizar, the middle star of the Big Dipper
handle, is one of these
Visual Binaries

Visual Binaries
 Are
far enough apart
to “see” their
individual motions
Spectroscopic Binaries

Spectroscopic
Binaries
 Very
close; cannot
be seen, but their
spectra tell the
story
The H-R Diagram

In 1912, Danish astronomer Ejnar Hertzsprung and
the American astronomer Henry Russell
independently found that plotting stars on a
diagram according to their luminosity and
temperature, placed them along a smooth curve on
the chart.
H-R Diagram
Mass-Luminosity Relationship

The larger a stars’ mass, the larger its luminosity will
be
 Main
sequence stars obey this relationship
Variable Stars




Stars that do not have a constant luminosity
Most stars, even our sun. vary slightly
Some may change luminosity by a factor of two or
three
Some pulsate at regular intervals, others are erratic
= irregular variables
STELLAR EVOLUTION
STELLAR EVOLUTION
What is Stellar Evolution?


The stages a star goes through from birth to death.
2 types of star groupings
 Low
mass = 10X our sun or smaller
 High mass = 10X our sun or larger

The size of the start determines the phases it will go
through in its life.
Low Mass Star Sequence
1.
2.
3.
4.
5.
6.
7.
Intersteller cloud
Begins to collapse
A few Million Yrs.
Grows smaller & hotter
Hydrogen converts to helium
OUR SUN NOW
(Large
10 billion yrs. (our sun is in the
Yellow phase)
Middle of this stage
Hydrogen runs low, gets hotter & burns fast
Pressure pushes surface outward
Low mass sequence cont.
8.
9.
10.
11.
Sun Grows in size to become a RED GIANT
It shrinks, grows hotter and becomes YELLOW
GIANT
It grows again to a larger RED GIANT
Shrinks to WHITE DWARF
Low & High Mass Sequence
Size Comparison of Sun, Earth & Red Giant
Yellow Giants & Pulsating Stars


Most yellow giants are
aging High-mass stars
An unusual property of
these stars is swelling
and shrinking.
 Called
Variables or
Pulsating stars
2 Types of Yellow Giants
RR Lyrae




Mass comparable to
Sun
Yellow to White Giants
~40X the Sun’s
luminosity
Cycle is ½ day
Cepheid





Yellow Super giants
More massive than our
sun
Orange in color
100’s of X brighter
than our sun
Cycle is 1 day long
Why do Stars Pulsate?



Because their atmospheres catch some of the
radiation energy
When they expand, they can cool down and gravity
pulls them in again
Compresses gases then heats up and the cycle
repeats again.
Period - Luminosity Law


Period = time it takes to complete one pulsation
“The more slowly a start pulsates, the more luminous
it is”
Death of Stars like our Sun



Once the sun is a yellow giant, it is nearing the end
of its life
The sun will spend ~10 billion yrs consuming its
hydrogen and becoming a Red Giant
The evolution is faster toward the end of its life.
Ejection of Low-Mass stars’ outer layers




As these dying stars swell, some of the carbon and
silicon cools and flakes off
These flakes are pushed outward by the photons
pouring out of the sun
The debris becomes a translucent shell around the
hot core
We call this phase a PLANETARY NEBULA
Old age of Massive Stars




Massive stars (>10X our sun) DO NOT become
planetary nebula or white dwarfs
Other nuclear reactions take place that form heavy
elements (nucleosynthesis)
It is theorized that this is how all the elements heavier
than helium were originally formed
Heavier elements are made when the nuclei of
lighter elements combine.
Core Collapse of Massive Stars



The formation of an iron core, signifies the end of a
stars life
The pressure supporting the star came from
electrons, but they have been absorbed by protons
causing core pressure to drop
Like floors in an apartment building collapsing, the
layers of a star all fall inward, resulting in a huge
explosion = SUPERNOVA
SUPERNOVA EXPLOSION
Artists rendition
LIFE IN THE UNIVERSE
History of Life on Earth



Earth formed ~4.5 Billion years ago
The surface was probably molten rock for 1 billion
years.
We have found fossil algae & bacteria as old as
3.5 billion yrs.
 This
leads scientists to believe that life began rather
quickly, once conditions allowed it

Only simple algae& single celled organisms existed
until ~600 million years ago.


Mammals & Dinosaurs appeared ~250 mill. Yrs. Ago,
then later wiped out 65 mill. Yrs. Ago.
Hominid (our ancestors) appeared 5.5 mill. Yrs. Ago.


Earth has existed ~10,000 times longer than we have as a
species
Homo sapiens evolved only about 500,000 yrs. Ago.

If all of Earth’s history was compressed into a year, humans
would not appear until the last hr. and civilization in the last
few minutes
Unity of Living Beings

All living things use the same kinds of atoms for
structure and function (hydrogen, oxygen, carbon,
nitrogen and iron)
 These
elements are also abundant throughout the universe.
 We are made up of primarily the same “stuff” that is in our
atmosphere and ocean

One level up from this, is our use of amino acids
 We
use all the same amino acids to build proteins
 Ex. Scales of reptiles, scales on fish, stiff cartilage in our own
bodies


Every living thing passes on its genetic info via DNA
(same molecule for EVERYTHING)
The cells of EVERY organism uses the same chemical
processes to move important molecules into and out
of all cells.
Deductions from the Unity of Life

What conclusions can we draw from the chemical
similarities of living things?
 It
almost certainly suggests that all life on Earth had a
common ancestor or origin
Origin of Life on Earth


Most scientists today think that terrestrial life
originated from chemical reactions among complex
molecules present on a young Earth
Even Darwin believed this was possible, but the
experiment of Miller & Urey in 1953 bolstered the
argument
Miller-Urey Experiment



Filled sterile flask with water, hydrogen, methane,
and ammonia (similar to Earth’s early atmosphere)
Passed Electric spark through the mixture, emitting
visible and UV light (simulating lightening)
Result:
 By
the end of 1 week the mix contained a variety of
amino acids and organic molecules
What about Replication?



Today cells replicated using a double-chained
molecule (DNA)
Some researchers have speculated that earlier life
forms may have used a simpler molecule (RNA)
It has been shown that if the proper chemicals are
present, RNA can replicate in the absence of living
cells.
 IN
FACT, one particular mix of raw materials, the molecules
not only replicate, but MUTATE into a better replicator!!!!!
The Origin of Complex Organisms

The original cellular life on Earth was simpler than
the cells we see today, and probably had no
nucleus = PROKARYOTES
 Bacteria

and certain algae we see today are prokaryotes
These early prokaryotic cells may have merged with
other cells to enhance their success. These would
have become the EUKARYOTES
 Eukaryotes
are more complex cells that contain a nucleus,
and some other organized organelles


Random mutations caused some cells to survive
better than others, thus resulting in the “Natural
Selection” ideas of Charles Darwin much later.
The scenario described above about the origin of
life on Earth persuades many scientists that life
originated on Earth, HOWEVER some scientists
favor ideas that life originated elsewhere in the
universe and was transported to Earth.
Panspermia

The belief that terrestrial life descended from
organisms created elsewhere in the universe.
 According
to this theory, simple life forms (bacteria)
drifted from their place of origin across space to Earth.
 Ex:
dust particles moving through space carried bacteria from
some other planet and it ends up entering our atmosphere

This was a very popular theory in the 1920’s, but
critics point out that this theory does not simplify the
problem of the ORIGIN of life. I just shifts it
elsewhere, and adds the problem of getting it to
Earth.
Life Elsewhere in the Universe



Humans have speculated for thousands of years
about life elsewhere in the universe
Greek philosopher Epicurus & Roman scholar
Lucretius wrote ideas about living creatures on other
planets & even higher level creatures living
elsewhere in the universe.
HOWEVER, Plato & Aristotle argued that Earth was
the only place that life existed. This idea held
though the middle ages.



Today sci-fi movies and books open peoples minds
to the extra-terrestrial life forms
With no evidence, what can we say meaningfully
about life elsewhere in the Universe?????
ARE WE ALONE?
 “Many
Worlders” believe that Earth-like planets are
common, and would be surprised if there was no other life
 “Loners” suggest we are the only life in the Milky Way. No
radio contact suggests no other civilized planets.
Searching for Life Elsewhere

Radio searches – (SETI) Search for Extraterrestrial
Intelligence
 SETI
– uses receivers that automatically scan billions of
radio wavelength to search for signals from other
civilizations.
 Problems



with this search:
Some wavelengths are blocked by some molecules in our
atmosphere.
Other civilizations may not be transmitting radio waves at all,
they may just be listening
It may takes years for a signal to make its way through space to
a receiver
The Gaia Hypothesis



Proposed by Lovelock and U.S Microbiologist Lynn
Margulis
Suggests that life creates a single “larger entity”
with a planet, a “symbiosis” of life and planet
Living things alter their environment to make it more
hospitable (ex: oxygen and carbon dioxide levels)