Still hangin' around

Comet Tsuchinshan-ATLAS on October 19, 2024

The comet is climbing a little higher in the western sky after dark. Unfortunately, as it does so, it is moving further away from the earth and sun, which causes it to get smaller and dimmer each night. Technically, you could say it is still a naked-eye comet. But that would be misleading. It is more correct to say that if you know where to look and allow the sky to get dark enough, you can just barely see it. As always, binoculars help a lot, and so do digital cameras.

If you've been following the comet from night to night this week, perhaps you've gotten to know some of the stars and constellations beside it in the western sky. A good one to become familiar with is Corona Borealis, or "The Northern Crown." Although it's not a very bright constellation, you can see it without optical aid, as long as your night sky isn't too bright from city glow or moonlight. Its brightest star is magnitude-2.2 Alphecca, which means, rather blandly, "bright star of the broken ring of stars." 

What's so important about Corona Borealis? Surely you know! The news media have been blasting us with reminders about it since April, at least. The headlines say, "Bright Nova will Light up the Sky!" Well, I hate to spoil it for you, but the nova they're talking about is not going to light up the sky by any stretch of the imagination! The best we can expect for it is that it will be about as bright as Alphecca. Like the comet, you'll need to know where to look.

The star they're referring to is a long-period recurring nova. Since it is a variable star, it has been given a one-letter name "T," which is followed by its host constellation, Corona Borealis. Whenever astronomers use a letter or number along with a constellation as the name for a star, they use the genitive (possessive) form of the constellation. In this case, the star's name becomes "T Coronae Borealis." That is a little lengthy and awkward, so instead astronomers use the three-letter abbreviation of Corona Borealis, which is formally "CrB." So the star is more commonly known as T CrB (pronounced "tee cee-are-bee"). Yeah, I know, almost as clever as Alphecca! Another name for T CrB, however, is "the BlazeStar."

The BlazeStar spends most of its life at a very dim 10th magnitude (too dim for binoculars), from our vantage point here on earth. And then for whatever reason every (approximately) 80 years, it flares up briefly to 2nd or 3rd magnitude (2nd magnitude is brighter than 3rd magnitude, if you're wondering). The flareup is quite short, though. Only a couple of days, at most, and then the star begins to fade back down to 10th magnitude again for another 80 years, or so.

How do we know this? Because astronomers have witnessed its flareup. Um, twice. Once on May 12, 1866, and then again on February 9, 1946. Having observed T CrB turn briefly into the BlazeStar only twice in the whole history of humanity makes its period of 80 years, shall we say, a tad uncertain. One astronomer built a case that its period could be quite a bit shorter than 80 years. He predicted that the BlazeStar could flare up again sometime between April and September of 2024. And I guess his arguments were so convincing that he had all of us (and the news media, too) excited enough to spread the word and go outside every night to check on the star, to see if it flared up yet.

It takes a lot of patience and diligence to make nightly observations of a variable star. But you can bet that plenty of amateur astronomers want to become famous for being the first to spot it! I don't care about the 15 minutes of fame, but I really do want to see and record the flareup! And since nobody really knows when it's going to happen, the only way we're going to see it is to go out there every night and check on it. Probably some very lucky person will see it first and tell the rest of us about it. Hopefully, "the rest of us" will have a clear night very soon thereafter and get to see T CrB ablaze before it dims again! 

But it obviously hasn't flared up yet, and April and September have now both come and gone. As you may have noticed while spying on the comet, Corona Borealis is slipping away in the west as we approach the winter observing season. Soon it will be lost for a couple of months in the sun's glare. I certainly hope the BlazeStar doesn't flare up in the dark of the sun. If it does, then I also hope that some space telescope can keep an eye on it for us. To at least give us closure.

It is also quite possible that the BlazeStar won't follow its own pattern, if indeed, it can be called a pattern! Perhaps it will skip a turn and not flare up for another 80 (or some other number of) years. 

We needn't worry about these what-ifs, however. Not yet anyway. We still have more time in this viewing window. In spite of the fact that the April-September 2024 prediction didn't come true, if all we did is count the days between the 1866 and 1946 flareups, we can still expect the next flareup to occur on November 9th, 2025 (if I did my arithmetic correctly).

If you want to keep an eye on the BlazeStar, use my picture above as a reference. The circle next to T CrB is where it will be. And when it flares up, it will be about the same brightness as Alphecca.