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More than four months ago Betelgeuse, a very bright star that sits on the shoulder of Orion, began a dramatic fading that had some people speculating the supernova-in-waiting was about to explode. Astronomers thought that was unlikely, but were still intrigued by the cause of the dimming. The lowest dip came in mid-February, and since then the red giant has been brightening again, to the point that it even briefly became (very slightly) brighter than normal. Don't get too excited however, this isn't all that unusual for this variable star, and it's still not a sign an explosion is imminent.
Even highly stable stars like the Sun undergo some changes in output with time, but for a minority of stars these shifts in output are large enough for them to be classified as variable. Some variables are quite predictable and regular, something astronomers have found immensely useful as galactic markers, while others, are more erratic. Betelgeuse has cycles that run on different periods, some more regular than others.
Betelgeuse is listed as having a magnitude of 0.42, making it the 10th brightest star in the sky. However, it varies so much its official name is α Orionis despite usually being fainter than Rigel's (β Orionis) 0.18 (lower magnitudes are brighter). Back when the designations were being made it was probably going through a bright period. Being 1 percent above its usual average, as it was yesterday, is minor by comparison.
Consequently, the initial fading attracted little attention. Gradually, however, the dimming intensified until Betelgeuse had lost 63 percent of its glow, the faintest it had been in at least 125 years, temporarily removing it from the 20 brightest stars. It was even outshone by some of the stars of Orion's belt, its neighbors from our perspective.
This caught the world's attention, partly because Betelgeuse is such a familiar star, but also because it is considered the best candidate for a nearby supernova. As a red supergiant, there is no question Betelgeuse will eventually explode, outshining Venus and competing with the Moon, but that's likely at least 100,000 years away, much to some people's frustration.
What astronomers were less certain of was whether this was an internal effect with several cycles happening to combine, as initially assumed, or the result of a large “sneeze” or “burp” of dust. That debate may have a way to run, but currently the theory that dust contributed seems to be winning.
If you want to enjoy the red giant's recovered shine, however, you'd better be quick, as we're nearing the time of year where the Sun is close enough in the sky to outshine it at any (non-supernova) brightness.
