# ‪The Parallax Activity: Measuring the Distances to Nearby Stars‬

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Determining the position of a star or other object in three-dimensional space is an important concept in astronomy. Finding stellar longitude (called right ascension) and latitude (declination) is easy enough, but it is much harder to find the radial distance to those objects. This lesson teaches how the distances to nearby stars are measured using the parallax effect: as the Earth orbits our sun, the positions of the nearest stars seem to wiggle back and forth compared to more distant stars. Knowing this parallax angle and the distance from the Earth to the sun, we can use the tangent function to measure the distance to a star. In this lesson, students will learn how parallax is measured and will practice using trigonometry to measure the height of local landmarks. They will then conduct an activity measuring the distances to “planets” and their parallax angles to simulated stars, then calculate the stars’ distances. Each team of students will need a simple quadrant built from a one-meter ruler, a protractor, a piece of string, and a weight such as a rubber stopper. They will also need calculators or trig tables to do the final calculations. This lesson will take approximately 90 minutes to complete.