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ASTRO 101
Principles of Astronomy
Instructor: Jerome A. Orosz
(rhymes with “boris”)
Contact:
• Telephone: 594-7118
• E-mail: [email protected]
• WWW:
http://mintaka.sdsu.edu/faculty/orosz/web/
• Office: Physics 241, hours T TH 3:30-5:00
Text:
“Discovering the Essential Universe,
Fifth Edition”
by
Neil F. Comins
Course WWW Page
http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html
Note the underline: … ast101_fall2012.html …
Also check out Nick Strobel’s Astronomy Notes:
http://www.astronomynotes.com/
Homework/Announcements
• Homework due Thursday, October 25:
Question 6, Chapter 7 (What role did Charon
play in enabling astronomers to determine
Pluto’s mass?).
• Exam 2, Thursday November 1
Next:
Chapter 5 and Chapter 6: Other
Planets and Moons.
Comparing the Inner Planets
Next: The Giant Planets
The Giant Planets
• The giant planets are Jupiter, Saturn, Uranus, and
Neptune.
The Giant Planets
• The radii are between about 4 and 11 times
that of Earth.
• The masses are between 14 and 318 times
that of Earth.
The Giant Planets
• The radii are between about 4 and 11 times
that of Earth.
• The masses are between 14 and 318 times
that of Earth.
• However, the densities are between 0.7 and
1.8 grams/cc, and the albedos are high.
The Giant Planets
• The radii are between about 4 and 11 times
that of Earth.
• The masses are between 14 and 318 times
that of Earth.
• However, the densities are between 0.7 and
1.8 grams/cc, and the albedos are high.
• The planets are composed of light elements,
mostly hydrogen and helium.
The Gas Giants
• The composition of the giant planets,
especially Jupiter, is close to that of the Sun.
The Gas Giants
• The composition of the giant planets,
especially Jupiter, is close to that of the Sun.
• The internal structures of these planets is
completely different from that of the Earth.
The Gas Giants
• The composition of the giant planets,
especially Jupiter, is close to that of the Sun.
• The internal structures of these planets is
completely different from that of the Earth.
In particular, there is no hard surface.
The Gas Giants
• These planets are relatively far from the Sun
(more than 5 times the Earth-Sun distance),
so heating by the Sun is not a big factor.
Jupiter
• Jupiter is by far the most massive planet in the solar
system (it contains about 2/3 of the solar system mass
outside the Sun).
• It has the largest radius of any solar system planet, and
it rotates the fastest (once every 10 hours).
• It has at least 63 moons.
• In many categories, Jupiter is the most extreme case.
Jupiter’s Weather
• Owing to its rapid rotation, Jupiter has a very turbulent
atmosphere, which is composed mostly of methane
and ammonia (both hydrogen rich).
Jupiter’s Weather
• Owing to its rapid rotation, Jupiter has a very turbulent
atmosphere, which is composed mostly of methane
and ammonia (both hydrogen rich).
Jupiter’s Weather
• Owing to its rapid rotation, Jupiter has a very turbulent
atmosphere, which is composed mostly of methane
and ammonia (both hydrogen rich).
Jupiter’s Weather
• The most famous feature on Jupiter is the Great Red
Spot.
The Great Red Spot
• The Spot is at least
150 years old.
• It is basically a
giant hurricane,
roughly three
times the size of
Earth.
• Smaller features
are also evident.
The Great Red Spot
The Great Red Spot
• Similar storm
systems have
been observed to
form recently.
Jupiter’s Interior
• There is no way to directly
study the deep interior parts,
we rely on computer
models.
• The interior should be hot
(35,000 K), with a solid
core, possibly surrounded by
liquid.
• The gaseous outer
atmosphere surrounds
molecular and liquid
metallic hydrogen and
helium.
Jupiter’s Atmosphere
• The atmosphere of
Jupiter (and Saturn)
consists of poisonous
gas (ammonia and
ammonium
hydrosulfide) covering
a layer of water vapor.
Jupiter’s Moons
• Jupiter has 4 fairly large
moons, discovered by
Galileo in 1610, and at
least 59 other moons, all
significantly smaller.
Jupiter’s Moons
• The largest moon
is larger than
Mercury.
Image from Nick Strobel (http://www.astronomynotes.com)
Jupiter’s Moons
• The 4 Galilean
moons have small
rocky or iron
cores. They have
similar densities
to our Moon,
indicating that
each contains a
thick layer of
water and ice.
Io
• The surface of Io is unlike that of any other solar system
body. There are no impact craters, so its surface must
be young.
Io
• There are active volcanoes on Io, the only place in the
solar system outside of Earth where this is the case.
Io
• There are active volcanoes on Io, the only place in the
solar system outside of Earth where this is the case.
Volcanoes on Io
• Io’s surface is constantly altered by
volcanoes.
Volcanoes on Io
• Io’s surface is constantly altered by
volcanoes.
• On Earth, the energy for geological activity
comes from radioactivity.
Volcanoes on Io
• Io’s surface is constantly altered by
volcanoes.
• On Earth, the energy for geological activity
comes from radioactivity.
• However, Io’s mass is relatively small, so it
should have no radioactivity left.
Volcanoes on Io
• Io’s surface is constantly altered by
volcanoes.
• On Earth, the energy for geological activity
comes from radioactivity.
• However, Io’s mass is relatively small, so it
should have no radioactivity left.
• The heating source turns out to be Jupiter’s
gravity, which compresses Io as its orbits.
Europa
• Europa has a very
smooth surface,
and it may have
an ocean of liquid
water underneath
the surface.
Europa
• Europa has a very
smooth surface,
and it may have
an ocean of liquid
water underneath
the surface.
• Could there be
primitive life?
Other Jovian Satellites
• The rest of
Jupiter’s moons
are small and have
an irregular shape.
• These may be
fragments of a
once larger body
or captured
asteroids.
Jupiter’s Rings
• Jupiter also has dark rings, discovered by Voyager in
the late 1970s.
Next
Saturn
• The most obvious feature of Saturn is its large ring
system, which has been known for more than 300 years.
Saturn’s Atmosphere
• The composition of Saturn is similar to that
of Jupiter.
• Saturn also rotates rapidly, once every 10
hours or so.
• Saturn’s weather is like that on Jupiter,
although the contrast between different
bands is much less.
Saturn
• Note the band-like structure in the clouds.
Saturn
• Note the band-like structure in the clouds.
Saturn
• The rings are very thin, and gaps are evident, even from
the ground. They consist of fragments of ice and icecovered rocks.
Saturn
• The rings are very thin, and gaps are evident, even from
the ground. They consist of fragments of ice and icecovered rocks.
Saturn
• Small satellites can cause some of the rings to ripple or
to have braided structure.
Saturn
• Small satellites can cause some of the rings to ripple or
to have braided structure.
Saturn’s Rings
• From Voyager, we know the rings are composed of
hundreds or thousands of “ringlets”.
Saturn’s Moons
• Saturn has 1 very
large moon (Titan),
10 moderate size
moons, and a few
dozen much smaller
ones.
Saturn’s Moons
• Saturn has 1 very large moon (Titan), 10 moderate
size moons, and a few dozen much smaller ones.
Saturn’s Moons
• Saturn has 1 very
large moon (Titan),
10 moderate size
moons, and a few
dozen much smaller
ones.
• Titan is the only
moon with an
atmosphere.
Titan
• Titan’s atmosphere
is mostly hydrogen
with a substantial
amount of methane.
• There are organic
molecules, but it is
probably too cold
for life to have
evolved.
Titan
• There are lakes of liquid methane, as well as large flat
areas.
Uranus and Neptune
• These distant planets were not known
before the invention of the telescope.
• They are each about 4 times the diameter of
the Earth, and about 15 times more massive
than the Earth.
• They are made up mostly of H and He, but
with a bit more heavy elements.
Uranus and Neptune
• Both planets appear blue-green because of the methane
gas mixed in with the hydrogen.
• The weather patterns are much less apparent.
• Solar heating is not important since they are far from the
Sun.
Uranus and Neptune
• Both planets appear blue-green because of the methane
gas mixed in with the hydrogen.
• The weather patterns are much less apparent.
• Solar heating is not important since they are far from the
Sun.
Uranus and Neptune
• Both planets are believed to have rocky cores surrounded
by compressed water and liquid hydrogen and helium.
Seasons on Uranus
• The rotation axis of Uranus is inclined by about 90
degrees relative to its orbital plane. This gives rise to
highly exaggerated seasons.
Uranus’s Rings
• Uranus also has
rings, which were
discovered in 1977
when Uranus passed
directly in front of a
distant star.
• They are very dark,
reflecting only about
2% of the sunlight.
Uranus’s Rings
• Uranus also has
rings, which were
discovered in 1977
when Uranus passed
directly in front of a
distant star.
• They are very dark,
reflecting only about
2% of the sunlight.
Uranus’s Rings
• Uranus also has
rings, which were
discovered in 1977
when Uranus passed
directly in front of a
distant star.
• Recent advances in
telescopes and
cameras allow for a
better view than was
previously possible.
Uranus’s Rings
• Recent advances in
telescopes and
cameras allow for a
better view than was
previously possible.
• Note the system of
moons that orbit in the
equatorial plane. They
take their names from
Shakespeare’s A
Midsummer’s Night
Dream and other
works.
Neptune’s Rings
• Neptune also has dark rings, discovered by Voyager
in the late 1980s.
Rings
• All of the gas giants have rings, although
the rings of Saturn are by far the largest.
• They appear to be relatively short-lived
(only millions of years) and composed of
material from moons that wandered to close
to their parent planets.
Neptune’s Moons
• Neptune has at least 13 moons, most of which appear
to be captured asteroids. The largest moon, Triton,
was captured into a retrograde orbit, and will soon be
destroyed by Neptune’s gravity.
Next:
Chapter 7
(Dwarf Planets and Small
Solar System Bodies)