Homework Set 2 -- Due Sept 15



1) Mars is approximately 1.5 A.U. from the Sun. Now imagine yourself living on Mars. How often do you see the Earth in opposition? (Think about whether Earth is an inferior or superior planet if you're a Martian.)
Once every Martian year
Once every Earth year
Once every 2.19 Earth years
Never


2) Which of Galileo's observations was in immediate and direct contradiction with the Ptolemaic (epicycle) model of the solar system?
the phases of Venus
spots on the Sun
craters on the moon
moons of Jupiter
You could make an argument for the moons of Jupiter, but the phases of Venus is a better answer -- they can ONLY be explained by Venus orbiting the Sun.

3) Consider two planets, A and B, orbiting a distant star. Planet B orbits twice as far from the star as Planet A does. How does Planet b's orbital period compare to Planet A's?
Half as long
the same
twice as long
more than twice as long


4) Suppose the Moon kept its mass (and its location in space), but somehow was shrunk in size to the radius of a small marble. (Yes, such an object would be very, very dense.) Or better yet, suppose the Moon got squeezed down so much (keeping its same mass) that it became a black hole. (We will learn more about those things later in the course.) What would happen to the Earth?
The increased gravitational pull of the Moon would cause the Earth to spiral in towards the Moon.
The increased gravitational pull of the Moon would cause the tides on the Earth to increase.
The increased gravitational pull of the Moon would distort the Earth's orbit about the Sun.
All of the above
Nothing at all would happen to the Earth.


5) Newton's universal law of gravity was able to explain which of the following?
why no one could detect stellar parallax
All three of Kepler's laws
why the Sun rises and sets
the seasons