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Astronomy: Watching the
Sky
Class 2:
A Trip through the
Solar System
The Solar System
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•
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One Star – The Sun
8 Major Planets
5 dwarf planets
70 + moons
• Unknown number of
comets
• Unknown number of
asteroids.
Our Voyage
• We will be traveling outward from the
center of the solar system (the sun)
to edges of the system.
• Our voyage will take us 40
astronomical units (AU) from the
sun. An AU is the distance from the
sun to the Earth. About 93 million
miles.
The Sun
• A medium sized star.
• The largest object in the
solar system.
• 99.8% of the material
in the solar system is in
the sun.
• 70% of the sun is
hydrogen gas. 28%
helium gas. 2% metals.
Affect on Solar System
• The more massive
the object the more
gravity it has. The
sun’s massive size
keeps the planets
from flying away.
• The sun “burns”
providing most of the
heat and light in the
solar system.
How the Sun “Burns”
• Under the intense
pressure at the heart
of the sun the nuclei
of the hydrogen
atoms “fuse” together
to make helium and
release energy in the
form of heat and light.
• This process is called
“Nuclear Fusion”
How Hot is the Sun?
• The surface is 10,000
degrees Fahrenheit.
(Steel melts at 2,500 degrees
and Iron boils at 5,000).
• The sun’s corona,
extends millions of
miles into space.
Temperatures in the
corona are over
1,800,000 degrees
Fahrenheit
How Big is the Sun?
• The sun
is
863,705
miles in
diameter
(108 times
the
diameter
of Earth)
The Sun = Gold Pixel
• 163,000 miles = 1 foot.
Solar Wind
• In addition to heat and
light, the Sun also
emits stream of
charged particles
known as the solar
wind.
• A solar flare can
greatly increase the
energy of the particles
and cause power line
surges and radio
interference.
• The solar wind is also
responsible for the
aurora borealis.
Mercury
• 1st planet out from the
sun (1/3 of an AU).
• 3,032 miles in diameter
(less than half the diameter of
Earth).
• Surface temperature
ranges from -298 to 800
degrees Fahrenheit.
• Almost no atmosphere.
• No life.
Mercury’s Orbit
• Mercury has no moons.
• It orbits the sun once
every three months.
• Mercury turns on its axis
about every four and ½
months (longer than it
takes to do an orbit.
• Because of this a Mercury
day (From on sunrise to
the next) lasts 6 months.
Planet Walk
Venus
• 2nd planet out from Sun (3/4 of
an AU).
• 7,520 miles in diameter. (About
the same as Earth)
• Considered to be Earth’s
“twin.”
• Year is 224 Earth days.
• Rotates backwards slowly. 243
earth days equals one day on
Venus.
• It was once though that
beneath the planet’s dense
clouds there might be life.
Now we know it is too hot.
Surface of Venus is Hot!
• Surface temperature as
high as 872 degrees
Fahrenheit (hot enough to
melt lead)
• Venus has a thick
atmosphere of mostly
carbon dioxide. This is a
“greenhouse” gas and
retains heat. This makes it
even hotter than Mercury.
• The atmosphere is very
thick.
Planet Walk
Earth
• 3rd planet from sun (1
AU).
• 7926 miles in diameter.
• Surface temperature 130 to + 105
Fahrenheit.
• Only known place that
supports life.
• Abundance of water.
Should really be named
“Ocean” not “Earth”
Earth Geology
• Only planet known to
have “plate tectonics.”
That means the crust
floats around on the
semi-molten mantel.
• This gives earth a
young surface with
lots of active
volcanoes.
• Axis is tilted 23
degrees.
Earth Seasons
Earth & Moon
• Earth has one
moon.
• Our moon is huge
compared to the
size of our planet
(1/3 diameter).
• Created when a
small planet hit the
Earth in ancient
times.
Moon
• Almost non-existent
atmosphere.
• No life.
• Only celestial body
man has walked on
besides Earth.
Earth without the Moon
• The ancient collision with
Earth has been called “the
lucky strike.”
• Earth without the moon
would have weak tides.
• Might be water covered with
no land.
• Day would only be 8 hours
long. High winds. No
seasons.
• Primitive life or no life.
Planet Walk
Mars
• 4th planet from sun
(1 ½ AU).
• 4,221 miles in diameter.
(1/2 that of Earth)
• Year =687 earth days.
• Day = 24hours, 37 mins.
• Two small moons: Phobos &
Deimos.
Mars History
• When astronomers
first looked at Mars
they thought they saw
“canals” on the
surface and changes
that suggested
seasons and plant life.
• Percival Lowell even
proposed the canal
were built by
intelligent Martians.
Mars in Popular Culture
• Writers have
speculated
about life on
Mars.
• War of the World
by H.G. Wells.
• Edgar Rice
Burroughs wrote
about a
civilization on
Mars.
More Mars Fiction
• Even I did a book
with featuring an
alien from Mars…
Mars Surface
• Better observations
over time show no
canals.
• Mars has a thin
atmosphere of carbon
dioxide.
• Mars is cold. Avg. temp
-67 Fahrenheit. (About
as cold as Earth arctic
regions).
Planet Walk
Asteroid Belt
• Asteroids are small rocky bodies
that orbit the sun.
• Most are located in a belt that is
2-4 AU from sun.
• They are too small to be round
like planet.
• Several hundred thousand
asteroids have been found.
• If all the asteroids in the solar
system were put together they
would be smaller than our moon.
Planet Ceres?
• Giuseppe Piazzi discovered the
first asteroid, Ceres, in 1801.
• At first it was considered a
planet until the thousands of
other objects around it were
discovered and named
asteroids.
• Ceres itself was reclassified as a
dwarf planet in 2006, though
some still consider it an
asteroid.
Planet Walk
Near Earth Asteroids
• Most asteroids stay in
the belt, but some do
approach Earth.
• Small ones become
meteors if the enter
Earth’s atmosphere
and meteorites if they
hit the ground.
• Large ones can be
dangerous to Earth
Asteroids & Extinction
• An asteroid named
Chicxulub is often
cited as the reason
for the dinosaurs
extinction.
• Chicxulub is thought
to be 6 to 12 miles
across.
• It made a crater 130
miles in diameter.
Jupiter
• 5th planet from the Sun (5
AU)
• Largest planet in solar
system – 88,846 miles in
diameter. (11 times the
diameter of Earth)
• Year=12 Earth years. Day=9
hours, 55min.
• It is a gas giant planet.
Has no solid surface, but
is composed of gas.
• Temperature: -162
Fahrenheit.
Jupiter’s Red Spot
• Jupiter is mostly
composed of hydrogen
gas.
• Its most noticeable
feature is the “Great
Red Spot”
• The spot is a storm
that has been raging
for at least 300 years
and could hold two
Earths.
Jupiter Moons
• Galileo discovered
Jupiter’s four biggest
moons in 1610: Io,
Europa, Ganymede and
Callisto.
• Jupter has 16 named
moons, but probably
many more small ones
not named or
confirmed.
Jupiter’s Moon Europa
• Is of special interest because
it appears to have a frozen icy
surface with liquid water
underneath.
• Water is kept warm by tidal
forces.
• One of the few places
besides Earth with large
amount of liquid water.
• Scientists speculate about
life in the water.
Planet Walk
Saturn
• 6th planet from sun
(10 AU).
• A gas giant 74,897
miles in diameter (10
times the diameter of
Earth).
• Year = 29 ½ Earth
years. Day 10 hours.
• Most noticeable
feature are its rings.
• 18 named moons.
• Temperature -360 F
Planet Walk
Uranus
• 7th planet from sun (19 AU)
• A gas giant 31,763 miles in
diameter (4 times that of
earth)
• Its rotates on its side.
• Year = 84 Earth years. Day
= 17 hours
• 27 named moons.
• Temperature –355 F
• Discovered by William
Herschel in 1781
Planet Walk
Neptune
• 8th planet from sun. (30
AU).
• Temperature -400 F.
• A gas giant planet.
• Year = 164 Earth years.
Day = 16.11 hours
• Diameter is 30,777
miles (4 times that of
Earth)
• 8 moons
English Lose a Planet
• Predicted first in 1845 by
Englishman John Couch
Adams, but he could not get
anyone with a telescope to
look for it in the sky.
Eventually and Frenchman
Urbain Le Verrier also
predicted it and the two had
to share the credit.
Planet Walk
Kuiper Belt
• A belt of asteroids out
beyond Neptune (30 to
50 AU).
• Also contains dwarf
planets like Pluto,
Eris(right), Makemake and
Haumea
• Belt also contains
comets.
Comets
• Small bodies “dirty
snowballs” that mostly
reside in the Kuiper belt or
further out in the Oort
Cloud.
• Some are on an elongated
orbit that brings them
though the inner solar
system and near the sun.
• As they get close to the sun
the ice melts an the comet
gets a tail.
Comet Orbit
Group Discussion: Comet Fear
• The inhabitants of Earth feared their planet
passing through a comet’s tail in 1910.
Discuss the following:
– Why have people always feared comets?
– What especially in 1910 concerned them?
– Do you think their fears reasonable?
– Do you think there any way a comet could do
damage on earth?
– Without comets would there be life on Earth?