HW #1 (Due 9/2)
1. Explain the concept of “look-back time”. Do this in two different ways.
a. If radio astronomers receive a signal from an intelligent civilization in the Andromeda
Galaxy (M31), how long ago did the extraterrestrials send the message? Explain your
b. On December 8, 1941, Franklin Roosevelt’s “Day that will live in infamy” speech
was broadcast over the radio. If an extraterrestrial civilization is listening in to our
broadcasts and today they hear this famous speech coming from the Earth, how far
away are the extraterrestrials? Explain your reasoning and solve the problem.
2. Explain the difference between the terms, Solar System, Galaxy and Universe. Include
in your explanation the difference in scale (size).
3. The Earth is 1 astronomical unit from the Sun (A.U.). Jupiter is 5.2 A.U. from the Sun.
It takes light from the Sun about 8 minutes to reach Earth. How long does it take light
from the Sun to reach Jupiter? Show your work.
4. Explain how the crescent phase of the Moon is different from a lunar eclipse.
5. You have very likely heard that “the Earth’s axis is tilted”. But the Earth is just orbiting
out in the universe. Out in empty space. Explain what the Earth’s axis is and explain
what it is tilted relative to.