Download Midterm - Department of Physics and Astronomy

Astronomy 204 – Midterm (Fall 2008)
Name: _______________________
The following exam is open book and open notes, however you are not allowed to confer
with any other students. There are 5 problems (with subsections) each worth 20 points. You
should show all of your work in an easily readable fashion and explain your reasoning in a
straightforward clear manner. Place a box around your final answers. Additional paper is available
if you need it. You have 75 minutes to complete this midterm. Good Luck!
1.
The small asteroid Lisana has a roughly circular orbit with a semi-major axis of 0.650 AU
and revolves about the sun in the same direction as the planets. (You should assume for this
problem that the earth’s orbit is circular as well and that the two orbits are coplanar.)
On December 31 at midnight (exactly as the new year begins), Lisana is at inferior
conjunction. How long until the asteroid is seen at greatest elongation? (Your answer should be in
days with 3 sigfigs. Your solution should also contain a well-labeled diagram that illustrates the
motion of the earth and Lisana.)
2.
(a)
Draw a horizon diagram for an observer on the Tropic of Cancer. You should label
the cardinal points, the zenith, the nadir, the horizon, the observer’s meridian, and both celestial
poles.
(b)
Then draw in (and properly label) the 3 major paths of the sun (equinox path, summer
solstice path, and winter solstice path). You should label the value of meridional altitude whenever
one of these paths crosses the observer’s meridian.
(c)
Draw in the sun at noon on November 21.
(d)
Draw in the approximate location of the waning crescent moon.
(e)
What is the sidereal time?
(f)
What is the hour angle of the moon?
3.
Calculate the following quantities related to a space probe being sent on a least energy orbit
to Saturn.
(a)
What is the semi-major axis of the least energy elliptical orbit? Make a drawing of this orbit
in the plane of the solar system as seen from near the NCP.
(b)
Relative to the Earth, what is the velocity of such a probe at the Earth’s orbit?
(c)
When the probe reaches Saturn, what is its velocity relative to that planet?
4.
(a)
Saturn’s moon Titan has an average albedo of 0.15. Use this to estimate the
equilibrium temperature of Titan.
(b)
Apply this temperature to the issue of retention of an atmosphere. Can Titan retain Carbon
Dioxide?
5.
(a)
The star HD 47362 has an absorption line in its spectrum corresponding to the
electron in the hydrogen atom jumping from level 2 to level 6. Calculate the wavelength of this
absorption line and describe its place in the electromagnetic spectrum.
(b)
If the star HD 47363 is moving away from the earth with a relative velocity of 665 km/s, at
what frequency (on average) would the absorption line be perceived by astronomers on the earth?
(c) If this absorption line is extremely strong in the spectrum from HD 47363, what can you
conclude about the surface temperature of the star? Fully explain how you know this and cite the
physical laws that provide this information.