Betelgeuse, a red giant in the constellation Orion, is normally one of the 10 brightest stars in the sky. For those navigating by sextant, it is  one of the 58 navigational stars. Recently, however, it has begun to dim and is now fainter than ever recorded. What is happening?

Jonathan Corum writes in the New York Times: Betelgeuse typically fades and brightens in short cycles of 14 months and longer cycles of about six years. Overlapping cycles might explain the dimming, or clouds of debris might be obscuring the starlight. Or the star might be about to explode. …

Betelgeuse will keep burning until the atoms in its core finally fuse into iron and the star runs out of fuel. When that will happen is unknown — perhaps next year, perhaps 100,000 years from now.

The star will collapse violently and then explode. The resulting supernova will release staggering amounts of energy and create a burst of even heavier elements as it casts debris out into space.

For a while, the dying star will be visible in the daytime and shine as bright as the moon.

While next year or perhaps 100,000 years from now is a moderately large time window in human terms, it is also possible that Betelgeuse has already exploded into a supernova. The star is 642.5 light-years away from the earth, which means that if the star exploded tomorrow, it would still take over 642 years for the light to travel through the vastness of space to reach the earth for anyone to see it.  Put another way, if sometime this year we observed Betelgeuse become a supernova, we will be witnessing an event that began over 600 years in the past.