Astronomy 121 1st Homework Assignment

Due Tuesday 7/26/11 in Class

1. Please go to the seasons simulation from the NAAP site located here: NAAP season simulation. Feel free to play with the simulation until you understand how it works. There are a lot of controls, so try all of them, including dragging the view of poles. Be sure to animate it. You can always click on the reset button to reset the simulation. Once you get a sense for how it works, reset it.

a) Under "star controls, select the Big Dipper. Find the lowest latitude that can view the Big Dipper. You can adjust the latitude by dragging the dot on the world map located on the lower left. This means all the stars in the constellation have risen above the horizon. Be sure to indicate whether it is degrees North or South or use a minus sign (-) to indicate degrees south. For example Auckland, New Zealand has a latitude of -37 degrees or 37 degrees South.

b) Do the same for the Southern Cross (you can unselect the Big Dipper), except find the highest latitude North that can see the Southern Cross

c) What happens to the circumpolar region as you get further away from the Poles?

2. Ranking densities:

Rank the following planet densities from most dense to least dense. In order to do this, you will need to compute the volume and then density of each planet. For example, a planet of mass =1 and radius 1 has a volume of (1)³ and a density of 1/1 = 1. To get you started, the density of planet A is 1/(2)³= 1/8. For each planet, show your work computing the volume and density. Then lastly list out the planets in greatest to lowest density. If two planets have the same density, please indicate so.

Planet	Mass	Radius
Planet A	1	2
Planet B	2	1
Planet C	3	2
Planet D	½	2
Planet E	¼	½

3. Galileo:

a) Why were discovering & observing Jupiter’s moons such an important event in humanity?

b) How did Galileo’s discovery of Venus’ various phases dispel the Ptolemic model? In other words, think about which of Venus’ phases you would see in an Earth –centered model and a sun-centered model.

c) How did Tycho’s model try to account for Venus’ phases and yet preserve a geocentric model? Click here to help you answer the question. Be sure to click on Tychonian at the bottom right corner.

4. Kepler’s 3^rd Law (from NAAP lab):

Rank the orbital period from longest to shortest of the planets. If some planets have the same period, be sure to indicate it. To get full credit for this problem you will need to fully explain your reasoning…ie. how do you know one planet takes longer or shorter to orbit the Sun than another planet.

5. Tycho Brahe’s parallax experiment to test whether or the Earth rotated around the Sun was ingenious and should have worked. Why didn’t it?

6. Explain the balance condition according to Newton's laws for an orbit to be stable. Or try to answer the following: Why the moon doesn't crash into the Earth?