Reflection and Discussion 1. The special properties of right triangles can be applied to large and small triangles. Extend one arm in front of you with a finger pointing up. Describe what appears to happen as you blink back and forth. This apparent change in position is called parallax, and it can be used to measure distances to the stars.
Scientists calculate the position of a star against the background of more distant stars.
As Earth moves in orbit around the Sun, the apparent position of the star changes. Scientists can measure the angular shift in the star's position from the first sighting to second sighting. Half of this angular shift is the parallax angle. Since we know the parallax angle and the distance from the Sun to Earth, we can use our knowledge of triangles and ratio to calculate the distance to the star. Repeat the exercise in number 2 to see how moving the finger closer or farther from the eyes affects the apparent shift.