How do astronomers measure the speed of a moving star?
Quick Answer
They use the Doppler shift of the star’s spectral lines: lines shift toward blue if the star is moving toward us and toward red if it is moving away. This reveals the star’s radial velocity.
The Full Story
When a star moves relative to Earth, its light waves are compressed or stretched, shifting the positions of spectral lines. A blue shift means the star is approaching, while a red shift means it is receding. By measuring that shift precisely, astronomers determine the star’s radial velocity, the component of motion along our line of sight. This technique has been crucial for finding binary stars, studying stellar orbits, and detecting exoplanets through the wobble they induce in their host stars. It is one of the core tools of modern observational astronomy.
Key Facts
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