# Calculating the Distance to Nearby Stars: The Stellar Parallax

Understanding Earth’s place in the universe has been a question in the minds of humans for millennia. From the first applications of astronomical trigonometry in Babylon, Egypt, Greece, or ancient Islam, to the precise astrophysical calculations used by astronomers in modern-day society — the human race has unremittingly pursued our cosmic address.

Trigonometry, the study of relationships between side lengths and angles of triangles, is a branch of mathematics dating as far back as 5,000 years ago. Largely regarded as an unremarkable subject of math today, trigonometry once revolutionized our species’ scientific capabilities, and unknown to most, continues to do so.

The trigonometric parallax is a method to discern a star’s distance from Earth. Parallax refers to the apparent change in the position of a given object depending on the observer’s line of sight, with respect to more distant “stationary” objects. When you hold your thumb out in front of your face and alternate opening and closing each eye, the position of your thumb moves, while the background appears to stay fixed. The distance your thumb appears to move is directly related to how far apart your eyes are.

The same principle can be applied to astronomical bodies. We may use trigonometric functions to calculate the distance of…