The Doppler Effect Explained

This is a rather informative article out of MIT that is suitable for everyone. If you are ever curious on how astronomers can tell what elements are present in stars that are very far away, and how fast that celestial body is moving, this article will give you a good general idea on how such a determination is made.

In astronomy, that source can be a star that emits electromagnetic waves; from our vantage point, Doppler shifts occur as the star orbits around its own center of mass and moves toward or away from Earth. These wavelength shifts can be seen in the form of subtle changes in its spectrum, the rainbow of colors emitted in light. When a star moves toward us, its wavelengths get compressed, and its spectrum becomes slightly bluer. When the star moves away from us, its spectrum looks slightly redder. 

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