# ASTR 109 HOMEWORK #3 Hints (Hamilton) due Wednesday August 6

1. The purpose of this problem is to show you what average density of a planet tell us about its composition.
DO: think about a number of Earth-sized planets made from different materials - all rock, all iron, all ice, 1/2 rock and 1/2 ice, etc. Would these planets be heavier than Earth or lighter? Now turn it around to use Earth's measured density to tell us about what it might be made of.
DON'T: just look up planetary compositions on a website! That will help a little, but I am much more interested in seeing you apply your own logic to this problem.

2. Some people are having difficuly with finding the reload or refresh button on their browsers. Look near the top left on your browser for button that reloads the webite. On Firefox and Safari it is a little arrow going in a circle.

3.c) One property of an elliptic orbit around the Sun is that it must smoothly increase from its minimum distance to its maximum distance and then return to the minimum distance. In a valid elliptical orbit there should never be more than two points at any given distance from the Sun! Check your picture to see if behaves correctly.

3.f) Don't forget question 3f on the back of the page!