## Deriving the Parallax formula

### Deriving the Parallax Formula

Surveyors on Earth use triangulation to determine distances. Astronomers use stellar triangulation, or parallax, to determine the distances to stars. If you consider the distance to the star from the Sun equal to the radius of a very large circle with the star at its midpoint, then:

^{o}), we can use the 'small angle approximation', and say that tan(p) is approximately equal to p (if p is measured in radians).

**defined**so that if the parallax angle is measured in arcseconds from the Earth at six month intervals, the distance to the star is in parsecs.

- 1 parsec=206,265 AU
- 1 parsec=3.0857X10
^{16}m - 1 parsec=3.2616 light years

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