Why do astronomers use parallax to measure nearby stars?
Quick Answer
As Earth orbits the Sun, nearby stars shift slightly against the background of distant stars. That tiny apparent motion gives their distance.
The Full Story
Parallax is the same effect that makes a nearby object appear to move when you look at it from different positions. In astronomy, Earth’s orbit provides a baseline of about 2 astronomical units from one side of the year to the other. By measuring the small angle shift of a nearby star relative to distant background stars, astronomers can calculate its distance. The European Space Agency’s Gaia mission has measured parallaxes for well over a billion stars. This method is one of the foundations of the cosmic distance scale.
Key Facts
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