Stellar Parallax

A parallax is a phenomenon caused by observing an object from two different observation points, e.g. two eyes. If you hold up a finger and close your right eye and then close your left eye, it will look as if the finger moves relative to the background.

In order to get a parallax when viewing a far away object, lika a star, the two observation points must not be close to each other.

Move the earth!

The first star parallax was observed in 1838 by Friedrich Bessel. He found that the star 61 Cygni had a parallax of 0.314 arcseconds, i.e. that the angle subtended by the star as the earth orbits the sun is 0.314/3600 degrees.

The unit for measuring the distance to stars is parsec, the parallax of one arcsecond.

The Hipparcos satellite


image from: NASA

Hipparcos=founder of trigonometry






by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License