Giant of uncertain temper

It’s Whit Sunday, or Pentecost, the 7th Sunday after Easter.

And Saturn is at west quadrature, 90° from the Sun. This is a stage at which the planet’s shadow is most clearly angled onto the rings, as shown in this detail from the Saturn section of Astronomical Calendar 2023.

At present, because of where the Sun is, you have to be in the southern hemisphere to get a view of the stars of Orion.

Betelgeuse. It’s our nearest red supergiant star It marks one shoulder of Orion, but is only coincidentally in front of the more distant blue supergiants that form the rest of Orion’s outline.

Its distance (uncertain) is about 500 light-years. It’s the way it is because of its mass, somewhere between 10 and 20 times that of the Sun. It is bloated to such a size that it can actually be resolved in large telescopes as a disk, with width about 0.05 of a second. If it were centered where the Sun is, then Mercury, Venus, Earth, Mars, and the asteroids would be inside it. Its radiation is spread over a vast surface, which therefore is relatively cool, therefore reddish.

Its usual brightness is about magnitude 0.45, similar to Achernar, making it the 10th brightest in our night sky. But it is a semi-regular variable, pulsating. It varies between magnitudes 0 (like Vega) and 1.6 (like Castor), usually over a period of around 400 days..

There are recent developments, which astrophysicists are struggling to understand. In late 2019 Betelgeuse dimmed unusually. It is thought that it ejected a plume of matter that became a dust cloud around it. Then in 2020 this cleared; the cycle resumed at twice its usual speed and with greater than usual brightness.

Giant stars live short lives. Betelgeuse is less than 10 million years old. It is expected to explode as a supernova within 100,000 years. Since it is 500 light-years away, this could have happened already and the message is on its way to us – the sight of Betelgeuse becoming a “second Sun,” exceeding the supernovas of the past.

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