The movies above show the parallax motions of three different stars, A, B and C, with respect to the distant, "fixed" background stars. We can use the method of parallax to determine the distance to each of the three stars.

Let us begin by measuring the parallax angle p for 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!).
• Move the marked paper to line up with the scale to determine the size of the total shift in units of arc seconds (arcsec).
• Remember that the parallax angle p is defined as one half of the total shift.
• Now you can use the formula for parallax to determine the distance of the star in parsecs.
• For frequently-asked questions about parallax, visit this page.