The aging, bright-red supergiant star Betelgeuse has captivated sky watchers since antiquity. The ancient astronomer Ptolemy was one of the first to note the monster star's red color. It is one of the brightest stars in the night sky and appears even more luminous because it is so close to Earth, only 725 light-years away.

But the star also periodically changes in brightness, which was first noted in the 1830s by British astronomer John Herschel. Astronomers now know that the star expands and contracts, brightening and dimming, on a 420-day cycle.

However, in October 2019, the star dimmed dramatically and continued to become even fainter. By mid-February 2020, the monster star had lost more than two-thirds of its brilliance.

This sudden dimming has mystified astronomers, who scrambled to develop several theories for the abrupt change. Ultraviolet observations by the Hubble Space Telescope suggest that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse's surface.

Hubble captured signs of dense, heated material moving through the star's atmosphere in September, October, and November 2019. Then, in December, several ground-based telescopes observed the star decreasing in brightness in its southern hemisphere.

The giant star is destined to end its life in a supernova blast. Some astronomers think the sudden dimming may be a pre-supernova event. Betelgeuse resides in Orion, one of the most recognizable constellations in the sky. The mammoth star marks the right shoulder of the hunter.

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