Welcome to the 800^th issue of the Bad Astronomy Newsletter.

That’s a lot of issues. 800? What?

800 by itself isn’t all that interesting a number (it’s the area of a square with a diagonal of 40 — the diagonal is the square root of 2 times the length of a side, and the area is the length of the side squared, so (40/sqrt(2))² = 800), but dang, it is a lot of words totaled in this here newsletter. Close to a million, near as I can reckon, given as many of the issues are around 1,200 words.

When I hit an issue number that’s evenly divisible by the square of the number of fingers we have — issue number modulo(100) = 0, if you want more math, and who doesn’t? — I like to shake things up a bit around here, usually in the form of a new banner image.

I always try to pick something interesting, and sometimes familiar. In this case, it’s very familiar: Betelgeuse!

Yup, that bloated ruddy gas bag in the center of the banner is the red supergiant Betelgeuse, one of the brightest stars in the sky and yet so little understood. We know it’s massive and near the end of its life, so inevitably will go all supernova in the future. But how massive? How close to the end of its life? How supernova-y will it get?

OK, that last one may not make a lot of sense, but the star is still an enigma. It probably had about 25 times the Sun’s mass when it was first formed, but has been blowing a dense, slow wind of subatomic particles like the solar wind on steroids ever since. It’s lost a lot of heft, and is likely down to about 18 solar masses. But that’s a rough estimate.

We don’t know how old it is, though, Even its distance is hard to determine. It’s likely around 500 light-years from us, and in general a star that close can have its distance measured using parallax. But Big B is so bright it saturates modern detectors, making it hard to measure its exact position enough for this method. Other methods can be used but they aren’t as accurate.

As I recently wrote, we don’t even know if Betelgeuse has a binary companion or not. This plays into a lot of what we think we know about the star, including its lifespan! The star changes brightness (making it a variable star as we say in the parlance), and that depends on its internal mechanisms, which in turn depend on what’s going on in its core. Stars maintain their energy emission by fusing light elements into heavier ones; the Sun is currently fusing hydrogen into helium. Massive stars doesn’t become red supergiants until they start fusing helium, so we know it’s gotten that far. But it may already be fusing carbon, in which case it may only have a few centuries before it explodes. On the other hand, if the variation in its light is due to a second star, we’ve been fooled by the brightness changes, thinking they were internal; in that case the star has hundreds of millennia to go before kablooey.

You may remember The Great Dimming, when Betelgeuse dropped in brightness by a factor of three. That was shocking; you could go outside and look at it and see for yourself how dim it was! That was really weird. We now think it ejected a huge cloud of opaque dust which blocked its light, but the exact mechanism involved is very complicated and not well understood.

As it happens, Betelgeuse is now getting easier to see, rising in the east around 10:00, though earlier every night. It’s part of Orion, a constellation that dominates the winter skies, and is such an icon this time of year. All in all, a perfect time to display the star here. 

The photo was taken by my friend and fellow astronomer Adam Block, and he has a VERY high resolution version of it you can download, too. It’s worth examining; you can see countless stars, as well as patches of darker dust floating around too, some of it possibly illuminated by the light of Betelgeuse itself. It’s an astonishing shot, and one I’m glad I can use for my banner here.

Tomorrow is a “supermoon”, when the full Moon is at or near its closest approach to Earth on its elliptical orbit.

But also, this is, well, kinda BS. I’ll let this guy explain:

@scientificamerican

If you go outside tonight you may be able to see the October supermoon, the closest supermoon of 2024. When the moon’s elliptical orbit re... See more

[Sorry about the tinny sound quality; I had to record this in my office which has terrible acoustics. But that is my Moon globe.]

Wanna know more? Read this whole article I wrote for Scientific American about this!

But go out and enjoy the Moon anyway. It’s pretty cool to look at.

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