Betelgeuse appeared orange-yellow nearly 2,000 years ago

Betelgeuse: Finally, the giant supernova's true color revealed after 2,000 years

The Orion Constellation

Betelgeuse, 642.5 light years away from Earth, is the giant red star found in the upper left of the Orion constellation. Researchers used various historical sources to determine that Betelgeuse appeared as a bright yellow star come 2000 years ago.

The Chinese court astronomer Sima Qian wrote around 100 BC about star colors: white is like Sirius, red is like Antares, yellow is like Betelgeuse, and blue is like Bellatrix.

Some 100 years later, the Roman scholar Hyginus described that the star in the right shoulder of Orion has a color similar to Saturn — yellow.

Further evidence from ancient authors like Ptolemy suggests that Betelgeuse didn’t fit into the group of bright red stars like Antares and Aldebaran.

“From these specifications, one can conclude that Betelgeuse at that time was in color between the blue-white Sirius and Bellatrix and the red Antares,” says lead author Prof. Ralph Neuhäuser from the University of Jena.

The color of a star is a sure sign of its evolutionary stage. When the luminaries burn hydrogen thermonuclear fuel in their cores, they inflate and emit gases into space. This expansion leads to a decrease in their surface temperature, causing a transition from yellow-orange to red. This color change happened over thousands of years, which is relatively short according to astronomical standards.

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