Astronomy 115
Homework Assignment #2
Due Tuesday Sept. 26
For all homework assignments, write neatly, staple multiple pages, and
show your work, where appropriate. Do not turn in this page with the
homework.
 Pick two of the lunar phases from the list below
and for each, draw the arrangement of the Sun, Earth and Moon. Also
draw what the Moon would look like during that phase. (Phases to
chose from are: Waxing Crescent, First Quarter, Waxing Gibbous, Waning
Gibbous, Third Quarter, Waning Crescent and New.)
 In your own words describe why the Moon has phases.
 How did Ptolemy explain the retrograde motions of the planets?
 Chapter 2, "What if..." Question 29

What is special about the position and speed of the Earth
when it is at perihelion? Which law or theory tells us this?

Suppose a new asteroid was recently discovered which takes 557 months to orbit
the Sun once (that's equal to 16,700 days or 46.4 years.).
What is its average distance from the Sun? (Show your work.)

A.) Draw a picture of a few waves of red light, and label the wavelength,
λ_{red}.
Also draw a few waves of violet light, for comparison. How do they differ?
B.) Now draw a grain of sand (diameter roughly 0.2 mm) on the same scale.
About how many waves of red light would fit into a grain of sand? NOTE:
see "Astro Lingo" sheet for measurement units.
 Which types of electromagnetic radiation from space pass
through Earth's atmosphere to reach the ground?
 Chapter 3, Question 1
 Chapter 3, Question 18