Transcript Document

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
Homework/Announcements
• Homework due Tuesday, March 19: Question
6, Chapter 7 (What role did Charon play in
enabling astronomers to determine Pluto’s
mass?).
Comets!
•
http://earthsky.org/space/comet-panstarrs-possibly-visible-to-eye-in-march-2013
• Comet PANSTARRS should be viewable in the
western skies starting March 7. It will be close to
the crescent Moon on March 12.
•
http://earthsky.org/space/big-sun-diving-comet-ison-might-be-spectacular-in-2013
• Comet ISON might be very spectacular in
December, 2013, provided it survives its close
encounter with the Sun.
Comets!
NEXT:
Recent Events: Mars Rover
• http://cosmiclog.nbcnews.com/_news/2013/03/12/17285137-curiosityrover-sees-life-friendly-conditions-in-ancient-mars-rock?lite
Evidence for Water on Mars
• These images and others suggest the presence of
liquid water on Mars, at least in the past.
Evidence for Water on Mars
• These images and others suggest the presence of
liquid water on Mars, at least in the past.
Life on Mars
• There is no evidence that there is currently
life on Mars. The recent Mars rovers will
perform additional experiments along these
lines.
• It is possible that there was primitive life in
the early history of Mars, but the only way
to be sure would be to go there.
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.
• 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 internal structures of these planets is
completely different from that of the Earth.
In particular, there is no hard surface.
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).
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.
• 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.
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)
The Discovery of the Outer
Planets
• Uranus was found in 1781 by William
Herschel. This new planet was barely too
faint to see without a telescope.
The Discovery of the Outer
Planets
• Uranus was found in 1781 by William
Herschel. This new planet was barely too
faint to see without a telescope.
• After many years of observations, it was
apparent that the orbit of Uranus was not
quite what was expected.
The Discovery of the Outer
Planets
• Uranus was found in 1781 by William
Herschel. This new planet was barely too
faint to see without a telescope.
• After many years of observations, it was
apparent that the orbit of Uranus was not
quite what was expected. The slight
deviations were probably caused by an
unseen planet’s gravitational pull.
The Discovery of the Outer
Planets
• After many years of observations, it was
apparent that the orbit of Uranus was not
quite what was expected. The slight
deviations were probably caused by an
unseen planet’s gravitational pull.
• Starting in about 1845, English and French
mathematicians worked out where the
unseen planet would be by using Newton’s
theory of gravity.
The Discovery of the Outer
Planets
• Starting in about 1845, English and French
mathematicians worked out where the
unseen planet would be by using Newton’s
theory of gravity.
• Neptune was located in 1846.
The Discovery of the Outer
Planets
• Starting in about 1845, English and French
mathematicians worked out where the
unseen planet would be by using Newton’s
theory of gravity.
• Neptune was located in 1846.
• In the early 1900s, it was thought that there
was still another more distant planet
(“Planet X”) disturbing Uranus.
Pluto
• Pluto was discovered in 1930 from Arizona.
Pluto
• Pluto was discovered in 1930 from Arizona.
• It is very faint, and appeared nearly point-like on
early photographs.
Pluto
• Essentially nothing was known about Pluto
until the 1970s.
 It is far from the Sun (more than 40 times the
Earth-Sun distance), hence it receives little
sunlight. In turn, we see very little light
reflected back.
 The planet looks nearly pointlike owing to its
large distance from us, so it was not possible to
see surface features.
Pluto’s Orbit
• Pluto’s orbit is highly inclined relative to the orbits
of the other planets.
Pluto’s Orbit
• Pluto’s orbit is also more eccentric than the orbits of
the other planets. The period is 247.7 years
Pluto’s First Moon
• Pluto’s first moon was
discovered in 1978.
• The orientation of the
moon’s orbit is such that
during certain times, Pluto
and its moon appear to pass
in front of each other every
3.2 days as seen from Earth.
Pluto’s First Moon
• Pluto and Charon passed in front of each other in the
late 1980s.
Pluto’s First Moon
Images from Courtney Seligman (http://www.cseligman.com)
• Pluto and Charon passed in front of each other in the
late 1980s.
• Studies of these events allowed astronomers to measure
the masses and radii of Pluto and Charon.
Pluto’s First Moon
• The masses can be
deduced from
Kepler’s Laws.
• The radii can be
deduced by looking at
the total brightness
over time.
Pluto’s First Moon
• Pluto’s mass is 1/500 of the Earth’s mass.
• Pluto’s diameter is 2300 km.
Pluto’s First Moon
• Pluto’s mass is 1/500 of the Earth’s mass.
• Pluto’s diameter is 2300 km. This is smaller than
Jupiter’s large moons, and also Earth’s moon.
More Moons for Pluto
• Two additional moons were found using the
Hubble Space Telescope in 2005.
Pluto “Demoted”!
• The definition of a “planet” was changed
recently:
– Planets: The eight worlds from Mercury to
Neptune.
– Dwarf Planets: Pluto and any other round object
that "has not cleared the neighborhood around
its orbit, and is not a satellite."•
– Small Solar System Bodies: All other objects
orbiting the Sun.
http://www.space.com/scienceastronomy/060824_planet_definition.html
New Classification Scheme for the
Solar System
• Many catagories overlap.
For example, some asteroids
are dwarf planets.
• In most cases, the
distinctions between the
catagories are not important
for us.
Dwarf Planets
• Ceres was discovered
in 1801 by Piazzi.
• Its orbit lies between
Mars and Jupiter.
• Thousands of
asteroids are now
known to be in the
“asteroid belt”.
• Ceres was
reclassified as a
dwarf planet in 2006.
Dwarf Planets
• Since 2003, three
additional dwarf
planets have been
discovered beyond
the orbit of Pluto.
• Eris, the largest one,
is apparently
composed largely of
water ice.
• Haumea appears to
be slightly oval
shaped.
Dwarf Planets
• Since 2003, three
additional dwarf
planets have been
discovered beyond
the orbit of Pluto.
• Eris has a very
eccentric and inclined
orbit. The period is
557 years.
Next
Small Solar System Bodies