A rapidly shrinking star named Betelgeuse—one of the largest known stars in the universe—is puzzling astronomers as it grows smaller. Betelgeuse is a supergiant 600 light-years away. It glows red and marks the left shoulder of the Orion constellation.

Scientists measured Betelgeuse in 1993 using an infrared instrument atop of Mount Wilson in Southern California. Using the same instrument today, the star has lost 15 percent of its former size. The reason behind the shrinking remains a mystery, but researchers did say they noticed a red spot on the star three years ago.

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