Image of astronomer Ptolemy, who distinguished Betelgeuse from other red stars.

2000 years ago, the red supergiant star Betelgeuse was actually yellow

Using historical descriptions and descriptions of Betelgeuse through the ages, scientists have been able to roughly determine when the supergiant star turned red.

The team found that the star, located in the Milky Way constellation Orion, about 640 light-years from Earth, changed from orange-yellow to red about 2,000 years ago. Betelgeuse is a red giant, and the stellar body goes through this phase after it burns out its hydrogen in the core, causing the core to collapse and the star’s outer layers to expand.

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