We have interesting opportunities this winter. Things in the night are changing their brightness. This is unusual: The constancy of the celestial firmament was for centuries an aspect of nature that represented constancy.
Of course we all know that the Moon nightly alters its phase, and therefore its brightness – which is why Juliet famously protested to Romeo, “O, swear not by the Moon, th’ inconstant Moon, that monthly changes in her circle orb, Lest that thy love prove likewise variable.” The big “inconstant” headline-maker these nights is the famous star Betelgeuse, because it’s dimmer than anyone has seen it in a century. And one of the planets is about to give us astounding degrees of brightness-alteration. Together they make this “inconstant brightness” topic a great reason to take a minute to look up.
With the Moon absent for the next ten evenings, it’s the perfect opportunity to step out or look through a window. Start with Betelgeuse (whose preferred pronunciation is BET’l’juice). If you can recognize the constellation Orion, you’re in business. It’s out all night long, and high enough to clear all trees and hills easily, starting around 7 p.m. in the east. For most people, the three stars in a row that form Orion’s belt are the most conspicuous part of the constellation.
To the upper left of the belt is a bright orange star, and this is Betelgeuse. It has been in all the news because it’s dimmer than anyone has seen it in more than a century. A few astronomers think it may be a sign that it will soon explode into a supernova. But most believe that that won’t happen for tens of thousands of years. Anyway, Betelgeuse is famous for altering its brightness, so “reading anything into this” is probably more sensationalist than it deserves.
But here’s the thing: Why wait to read about what it’s doing? Follow it yourself. It’s easy to do, really.
Any clear night – and this next week is absolutely perfect – look at Orion in the east, and compare Betelgeuse with Orion’s brilliant blue foot star Rigel. Which is brighter? A few times in history, they matched. But not normally, and certainly not these nights.
Now look way to the right of Betelgeuse to get to the first bright star in that direction. This also happens to be distinctly orange. This is the main star of Taurus the Bull, the famous Aldebaran. And that’s it. Simply see if Betelgeuse more nearly matches Aldebaran or more nearly matches Rigel. If it’s Aldebaran, then Betelgeuse is unusually dim; if Rigel, then it’s unusually bright. If halfway between the two, then Betelgeuse is at its normal brightness. By doing this, you can keep track of the strange fluctuations in the light of Betelgeuse all winter and spring. You won’t have to wait to read about it somewhere.
An even-bigger and more reliable (but less mysterious and ominous) brightness change involves the planet Venus. It’s that really bright star that’s low in the west these evenings at nightfall. It hovers just above where the Sun set.
For the rest of the winter and into the coming spring, keep watching Venus each evening at nightfall. You’ll see it gradually appear higher and higher up, and become increasingly brilliant. By March it will double its present brilliance and even be capable of casting shadows on snowy surfaces.
Between checking out Betelgeuse and Venus, you’ll find a strange and wonderful nocturnal pleasure in noticing when the light changes.
Sunday night’s Willow Observatory observation shows that Betelgeuse has faded further, though its spectrum is unchanged. It is now fainter than Aldebaran, and pretty much matches the light of Orion’s other (right) shoulder, the medium-brightness star Bellatrix. Extraordinary! The stuff of dreams. Orion has changed its appearance. Check it out!
Want to know more? To read Bob’s previous columns, click here. Check out Bob’s podcast, Astounding Universe, co-hosted by Pulse of the Planet’s Jim Metzner.