Trigonometric Parallax
If you hold a pencil at arm's length and alternately close your left and right eyes, the pencil appears to jump back and forth. This results from viewing the object from slightly different positions. Similarly, the positions of the stars should appear to shift as our viewing location is changed by the motion of the Earth around the Sun. This is an effect called stellar parallax. For more than a millennium, the lack of observation of stellar parallax provided the standard rebuttal to suggestions that the Earth might indeed move about the Sun. Because the stars are so very far away, this effect was not actually measured until 1837. In this activity, you will use your protractors and rulers to measure distances.

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