The movies above show the parallax motions of three different stars. Our ultimate goal is to determine the distance to each of the stars.

If you didn't get a copy in class, print out this Homework Answer Sheet. Fill in your answers to the questions below, then hand in the sheet at the beginning of the next class.

Let us begin by measuring the parallax angle p for each of the stars above:

• For each star, watch as the star shifts over the course of one year and measure the total shift from one extreme to the other (you might hold a piece of paper against the screen and mark on it with a pencil -- don't get marks or finger prints on the screen!).
• Express your answer in units of arc seconds (arcsec) using the scales above.
• Remember that p is defined as one half of the total shift.
• Write your answers for p on the Homework Answer Sheet.

We have learned about the geometry that causes the parallax effect (click for a reminder). The relative sizes of the Earth-Sun-Star triangles are different for the three stars.

• To make the large parallax angle seen for Star A, what type of triangle must exist -- short and wide or long and thin?
• What type of triangle must exist for Star B?
• Sketch the triangles for Stars A, B and C on the Homework Answer Sheet.

Which star is closest to the Sun: A, B, or C? Which is farthest: A, B, or C?

Imagine we had a star with a very large distance from the sun. How large do you expect the parallax angle to be for this star?

Make a general statement about the relationship between the sizes of p and d. Can you express this as an equation?