19 January 2020

The constellation of Orion hung magnificent above the driveway gate as I took the recycling out this cold and frost-bound evening.

In recent weeks, my Twitter feed has surfaced occasional tweets about the dimming of Betelgeuse. That’s the reddish, top-left star in Orion, as observed from wintry northern latitudes. The star is a variable-intensity supergiant, but the latest dip in brightness is more pronounced than ever. Its luminosity has dropped by almost 25% since September, and its radius is believed to have grown by about 9%.

Betelgeuse is known to go through a number of cycles of different periodicity. This is perfectly normal for an ageing (post main-sequence) star of this size. It’s thought the current impressive drop in luminosity is due to the alignment of a number of different low points in the various cycles. Talk of an imminent supernova seems premature—although on stellar timescales, that spectacular event is certainly not far off. Betelgeuse’s final blaze of glory will light up the sky for a few weeks, shining brighter than the full moon. Now wouldn’t that be something to witness?

As I gazed up at the familiar giant, his shoulder did indeed seem noticeably dimmer than usual. Would I have noticed, had I not read the tweets? Surely not. Which just goes to show how social media can occasionally have its uses—and how little attention we really pay to the familiar.

See also: Universe Today: Betelgeuse is Continuing to Dim! It’s Down to 1.506 Magnitude

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