Homework Set 3 -- Due Sept 22



1) The picture above is that of a C-141 Cargo aircraft, which has been modified (at considerable expense) to carry a 0.9-m telescope. This telescope and its instruments have been optimized to operate in a certain wavelength regime. At what wavelengths should this airborne observatory operate?
x-ray wavelengths
ultraviolet wavelengths
optical wavelengths
infrared wavelengths
radio wavelengths


2) Note how the sky changes color in the above image. The reason for this change in color is
the temperature of the Earth's upper atmosphere is different from that of the atmosphere near the ground.
the absorption lines of gases in the upper atmosphere are different from those of gases near the ground.
the emission lines produced gases in the upper atmosphere are different from those of gases near the ground.
the upper atmosphere is reflecting more moonlight than the atmosphere near the ground.
dust in the atmosphere is scattering sunlight.


3) In between us and a 6000 degree star is a cloud of cold gas. The atoms of this gas normally absorption line at 5000 Angstroms (= 500 nm) and 6000 Angstroms (=600 nm). However, the cloud of gas is moving away from us at a small but measurable speed. What will the spectrum of the star look like?
It will look like Spectrum A.
It will look like Spectrum B.
It will look like Spectrum C.
It will look like Spectrum D.
It will look like Spectrum E.
It will look like Spectrum F.
It will look like Spectrum G.


4) Imagine yourself as an astronaut orbiting the Earth. You look out the window of your vehicle and see a flare on the surface of the Sun. You know that solar flares emit light at all wavelengths. How long until your ship is hit by the dangerous x-rays and gamma-rays?
8 days
8 hours
8 minutes
8 seconds
No time at all. You are already getting hit by the x-rays and gamma-rays.


5) What produces the most light?
A 1-in sphere of iron heated to a temperature of 4000 degrees
A 1-in sphere of lead heated to a temperature of 3000 degrees
a 1-in sphere of hydrogen gas heated to a temperature of 6000 degrees
A 1-in sphere of liquid mercury heated to a temperature of 5000 degrees