PURPOSE: To show how stellar paralax is used to measure the distance to a star.
DESCRIPTION: A long vertical bar is placed a measured distance bewteen the students and the black board. Equally spaced marks are placed horizontally across the black board, as shown in the above photo.
The students cover one eye and, from thier seat, note where they see the verticle bar line up with the chalk marks on the black board. Next, the student moves thier head a measured amount to the side. The student again notes where they see the verticle bar line up with the markings on the chalk board. Using the information of the two observed positions, knowing how far they moved thier head, and given the distance of the vertical bar from the chalk board they can use paralax to estimate the distance between their seat and the chalkboard.
EQUIPMENT: Vertical bar, as photographed.
Updated by Jun Qi in 3/20/2000