AY C10 / L&S C70U Fall 2006
Nicholas McConnell, GSI
Asteroids
In The Empire Strikes Back, Han Solo narrowly evades a legion of TIE fighters by
successfully navigating through an asteroid belt (the odds of which are 3720:1, according
to C-3PO). How is this portrayal different from the asteroid belt (at least our solar
system’s) in reality? How would Solo have actually fared against the TIE fighters?
Suppose that in the year 2009, the Earth narrowly misses an encounter with a large
asteroid. Astronomers analyze the asteroid’s orbit and determine that, although it comes
close to the earth at the perihelion of its orbit (the point closest to the sun), it has an
average orbital distance of 4 A.U. When is the next time we have to worry about
possibly hitting the asteroid?
Extra-solar Planets
For several years, extra-solar planets were discovered almost exclusively by detecting the
periodic Doppler shift of stars. Recently, exoplanet discovery by transits—measuring the
decrease in a star’s brightness when a planet crosses in front of it—has become a very
promising astronomy topic, with multiple proposals to survey the sky for transiting
planets. What are some advantages and difficulties of the two methods of discovery
(Doppler shift and transits)?
AY C10 / L&S C70U Fall 2006
Nicholas McConnell, GSI
One of the more fascinating, still unresolved, mysteries about outer space is that very few
of the extra-solar planets we observe seem to have orbits similar to those in our solar
system! Either we exist in a very rare environment, or there are difficulties that have so
far prevented us from detecting extra-solar planets like Jupiter or Saturn. What might
some difficulties be?
Some notes:
The smallest extra-solar planets discovered so far have masses a few times larger than
Earth’s.
We discovered the first extra-solar planets about 10 years ago
Comets (Kuiper Belt and Oort Cloud)
Baseball analogy: if the location of a Kuiper Belt Object (KBO) relative to the Sun is
scaled to the location of an infielder relative to home plate, then a typical Oort Cloud
object is playing, say, right field. DEEP right field. In fact, if our KBO is covering first
base (90 feet from home plate), how far back is the Oort Cloud object?
Use the following:
Typical KBO distance: 40 AU
Typical Oort cloud distance: 20,000 AU
1 mile = approx. 5000 feet
AY C10 / L&S C70U Fall 2006
Nicholas McConnell, GSI
If comets were made out of solid rock instead of ice and small dust/rock grains, would
they ever break apart as they approached the sun? Would we be able to see tails on these
comets? Would they leave debris behind in our orbits, allowing us to see periodic meteor
showers?Stellar Brightness and Spectral Types
It doesn’t take a rocket scientist to notice that some stars in the sky appear brighter than
others. How do you expect the properties of many bright stars to compare to the Sun?
Must that be true for all bright stars, or is there something else that can make even the
dimmer ones appear relatively bright to us?
If we were on a planet orbiting a distant star, somewhere across the galaxy, would we be
able to pick out the sun in the night sky? If we knew exactly what part of the sky to look
in, would it be easy to see the sun with our naked eyes?
Parallax
One way astronomers determine the distance to stars is by measuring their parallax, half
of the angle by which they appear to move every half-year. How is parallax different
from the motions we measure for stars that have extra-solar planets orbiting them?
AY C10 / L&S C70U Fall 2006
Nicholas McConnell, GSI
Is it possible to use parallax to measure the distance to all the stars we can see? Which
stars does this method work best for?