# How do astronomers use stellar parallax?

##### 1 Answer

Parallax (the apparent change in position of an object due to a change in observation angle) is used to measure astronomical distances.

#### Explanation:

As the Earth orbits around the sun we observe stars from a changing position (about 300 million km maximum shift, twice the radius of the earth’s orbit) and the extent of the change is related to the distance of the object (normally a star) from us.

A diagram may help:

The formula for finding distance gives rise to the concept of a parsec, the distance at which a star appear to have one arcsecond (1/60th of 1/60th of a degree) of parallax, that being about 3.26 light years.

The scale is useful out to several hundred light years, but is increasing as telescopic resolution improves.

More details (perhaps more than you want!) here: https://en.m.wikipedia.org/wiki/Parallax