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ASTR101
Exam #2 Study Guide
Our Solar System
• Sun dominates mass of Solar System
• Mostly Hydrogen and Helium
• 99.8% of all mass
99 8% of all mass
• Jupiter is most of the rest of the mass
• Roughly 0.1% of the total
• Approximately the same as all the other Approximately the same as all the other
planets combined
• Planets “shine” mostly by reflected light from the Sun
from the Sun
• Two distinct types of planets
• Terrestrial or Inner plants
• Jovian or outer planets
Jovian or outer planets
• Each has its own set of characteristics
Terrestrial Planets
• Mercury, Venus, Earth, & Mars are similar in composition
• Small and rocky/iron
• Have varying atmospheres and geological activity
geological activity
• Only Earth has a significant Moon
• The Moon!
• Probably formed from an early collision
Jovian Planets and other
stuff
• Jupiter, Saturn, Uranus, and Neptune are all much more massive than Earth
• Primarily composed of H and He
• Most of the rest is water, methane, ammonia, and carbon dioxide (based)
Some small rocky/iron material in
• Some small rocky/iron material in core
• Consequence of formation location
• Jupiter and Saturn are still up e a d Sa u a e s
“collapsing” and releasing heat
• All have moons
• Some
Some are large, most are captured are large most are captured
asteroids
• Pluto is an example of a “dwarf planet
planet”
• There are many more!
Jovian Planets and other
stuff
• Asteroids are mainly found between Mars and Jupiter
• Remnants of a planet that did not form
• Mostly rocky and iron/nickel
• Comets are also remnants
• Icy
Icy leftovers in the outer solar leftovers in the outer solar
system
• Some rocky material as well
• Spectacular displays are icy material “boiling” off as they get close to Sun
• If either a large asteroid or comets hits Earth it would be a disaster!
• Possibly what killed off the y
dinosaurs
Solar System Formation
• Solar System formed from rotating cloud of gas & dust
t ti
l d f
&d t
• Conservation of angular momentum caused flattening into disk
• Planetesimals condensed and collided to form planets
• Happened about 4.5 billion years ago
• Hotter closer to young Sun, cooler farther out in disk
• Materials
Materials like rock and iron/nickel like rock and iron/nickel
condensed in inner solar system
• Icy materials in outer solar system
• Our Solar System is one example
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p
• Theory fits our system well
• Need to look at other planetary systems to see if we are common or unusual
Exoplanets
• Nearly 2000 planets known outside our Solar System
• First planets similar to those here was found in 1995
• Took a long time because of the difficulty of detecting planets around other stars
detecting planets around other stars
• Exoplanets have a large range of characteristics
• Mass of the earth to much larger than Jupiter
• Very close to their stars to very far away
V
l
t th i t t
f
• 0.01AU to 1000AU
• Some systems similar to ours, but others are very different
• Very difficult to detect exoplanets
Very difficult to detect exoplanets
• Even Jupiter is very faint compared to the Sun and has much lower mass
• Challenging to build equipment to see small effects
• Use
Use gravitational effects that induce small gravitational effects that induce small
motions
• Change in radial velocities tell about planet periods, mass, and orbital ellipticities
• Need inclination angle of orbital plane to remove ambiguities
Exoplanets
• Systems with transits are very valuable
y
y
• That there is a transit allows us to know the inclination angle of the orbit
• Allows for direct measurement of exoplanet size, mass temperature etc
mass, temperature, etc.
• Kepler mission has found a large number of transits
• Other techniques can be used to find exoplanets
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• Gravitational microlensing
• Has seen systems similar to ours
• Estimates that ~1/3 stars have systems similar to ours
• Direct
Direct imaging can find planets relatively far from imaging can find planets relatively far from
star
• Many exoplanets detected have challenged theories of how planets form
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• Particularly “hot Jupiters”
• We have found a few potentially habitable planets
Distances to Stars
• Distance is important but hard to measure for objects outside the solar system
solar system
• Trigonometric parallaxes
• Uses the separation of the earth and Sun as a baseline
and Sun as a baseline
– direct geometric method
– only good for the nearest stars (~1000pc)
– Distance = 1/(parallax angle in arcseconds) in parsecs
• Units of distance in Astronomy:
– Parsec (Parallax second)
– Light Year
Luminosity and
Brightness
• Luminosity of a star:
• total energy output • independent of distance
i d
d t f di t
• Apparent brightness of a star:
• depends on the distance by the inverse square law of brightness
inverse‐square law of brightness.
• measured quantity from photometry.
Stellar Masses and Radii
• Types of binary stars
T pes of binar stars
• Visual
• Spectroscopic
• Eclipsing
clipsing
• Only way to measure stellar masses:
• Only roughly a few hundred stars
Only roughly a few hundred stars
• Radii are directly measured for relatively few stars.
Possible questions:
How do we know the mass of Mars? Mass of H
d
k
h
fM ?M
f
Venus? Which one is denser: Moon or Earth? (hint: assume the Moon formed from the outer h
f
df
h
parts of the Earth during an early collision)
Can density of a planet be lower than density of water?
Are there volcanoes on Mars? Venus? How are they the same or different compared to volcanoes on Earth?
Are there quakes on Mars? Venus? How are they the same or different compared to quakes on Earth?
Possible questions
How do we know the mass of d
k
h
f
Ceres (a large asteroid)?
Can comets have atmospheres?
Can comets have atmospheres? Volcanoes?
How are Jupiter and Saturn
How are Jupiter and Saturn similar? Different?
What else is in the solar system other than the planets?
Possible questions
Can planets still form in our Solar System?
C
l
ill f
i
S l S
?
Is the Sun older or younger than the planets?
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q
Can you think of another consequence of the discussed model of the Solar System origin?
Should other planetary systems resemble
Should other planetary systems resemble ours?
Suppose you found a star with the same mass as the Sun moving back and forth with a
as the Sun moving back and forth with a period of 8 months. What could you conclude?
the star has a planet orbiting at less than
the star has a planet orbiting at less than 1AU
the star has a planet orbiting at more than 1AU
than 1AU
Possible questions:
What makes it necessary to launch satellites into space to measure very precise parallax?
Would it be easier to measure parallax from Jupiter? From Venus?
Jupiter? From Venus?
Questions
• How much does the apparent brightness of stars we see in the sky vary? Why?
• Stars have different colors? So is the Stars have different colors? So is the
amount of light at different wavelengths the same?
• Can we tell the difference between a very Can we tell the difference between a very
luminous star that is far away and in intrinsically low luminosity star that is nearby?
Possible questions:
What does the temperature of a star mean?
Are there stars with temperatures higher than 50000K?
than 50000K?
Are hotter stars brighter than cooler stars? Are they more luminous?
What star do we know the mass of very precisely?
Why is it so unlikely that binaries are in eclipsing systems?
Most binaries are seen as spectroscopic. Why?
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