Caoimhín's Content

Today’s piece is mostly about the star Betelgeuse, however I will start the article the same way I started the video, by mentioning Culture Night. The 20th of September is Culture Night in Ireland, so it is coming up soon. If you are in Ireland, Culture Night puts on a lot of amazing events and often opens up areas that the public don’t normally get to see or keeps them open later than normal. There are events all around the country and many of them are worth a look. For the main subject, we need to push all the way through to the morning after Culture Night, through to the morning of the 21st at about 3 o’clock. This brings the constellation of Orion into view.

I’ve spoken about a Orion previously on this website, and when talking about Orion, it’s hard not to mention the lovely red star Betelgeuse. Given that we’re focusing on Betelgeuse this time around, I will be repeating the name over and over again, and I do normally pronounce it like Beetlejuice. There are plenty of other options. The English language doesn’t really have one central standard the way so many other languages do, French for example has the Académie Française which decides the standard for grammar and pronunciation. I pronounce Betelgeuse as Beetlejuice, but pronouncing this “se” at the end as a “z “is very common, as is pronouncing the first syllable as “bet” rather than “beet”. There are a few options, with the International Phonetic Alphabet, presented on Wikipedia page for Betelgeuse, including on for non-rhotic or “R-dropping” accents. If you say the word nurse without the “r” sound, as if it was “nuhse”, then pronouncing Betelgeuse to rhyme with nurse is another potential option.

Of course, these are all just approximations of the original Arabic. Many stars were originally named in Arabic, but Betelgeuse looks less like it’s original form than most. Betelgeuse was more than likely Yad al-Jawzāʾ, Orion’s hand. Al-Jawzāʾ does sound like the end of Betelgeuse, but Yad doesn’t quite sound liek the start. This is seems to be a mistake from the transliteration of the name. The Arabic language isn’t written in the Latin alphabet, there is an Arabic script which isn’t an alphabet, but I won’t get into the details of that here. To write Arabic words using Latin letters, it needs to be transliterated. In the Arabic script, it just so happens that the letter “y”, can look like the letter “b”, so Yad al-Jawzāʾ became Bad al-Jawzāʾ. “Y” in this case means the noise at the start of the word “yes”, a palatal approximant. In the video I just call it the “yuh” sound, but that might not work as well when written. I don’t speak Arabic so I would certainly butcher the pronunciation of Yad al-Jawzāʾ as well, but you might be able to see how someone mispronouncing that name might end up with Betelgeuse or Beetlejuice. It has as few other names as well, it’s sometimes called the Martial Star, and it is often associated with war and battle in many cultures.

Betelgeuse is widely regarded as one of the brighter stars in the sky, but how bright it is can vary quite a lot. Betelgeuse is a pulsating variable star, and the variable part refers to its variable brightness. At the moment, we’re seeing Betelgeuse at about magnitude 0.45, but this will usually be reduced by the air, especially if Betelgeuse is low in the sky. Usually, Betelgeuse is usually the 10th brightest star in the sky, but it can vary significantly. Betelgeuse can be as bright as the 5th or 6th brightest star in the sky, outshining Rigel comfortably, or it can dim all the way down to being around the 20th, fainter than Deneb. Deneb happens to be in the sky with Betelgeuse at moment, but far to the West, almost on the opposite side of the sky. There are times when Betelgeuse is not only brighter than Rigel but brighter than Capella. Capella has a magnitude of just 0.05, almost 0, making it almost as bright as Vega. Betelgeuse’s designation is Alpha Orionid. Being the Alpha star of a constellation usually means that it’s the brightest star. Unfortunately, isn’t always so straightforward, something I’ve covered on this website in the past. Rigel, down at the other corner of Orion, is designated Beta Orionid. Rigel however has a magnitude is 0.15, while Betelgeuse has a magnitude of just 0.45. Just like golf we’re aiming for the lowest number with stellar magnitude. The lower the magnitude the brighter the object appears, so Rigel is in fact brighter than Betelgeuse.

At least, Rigel is brighter than Betelgeuse right now. Generally speaking Rigel is brighter than Betelgeuse, but a few different things can affect our view and how bright the stars appear. Betelgeuse is disappearing with the rising Sun for us here in Ireland, before Betelgeuse even reaches its highest in the sky. For those of us in the Northern Hemisphere, Betelgeuse is higher up than Rigel. From Ireland, Rigel does get pretty high into the sky. If we were to travel to more northerly latitudes, we would see that Rigel stays quite close to the horizon even in the middle of the night, whereas Betelgeuse is at a reasonable height in the sky. We would be able to see that at a different time of year at least, even from quite far north right now it’s still the wrong time of the year to see Orion and those two stars in the middle of the sky. From far enough North, Rigel is quite low to the horizon, meaning its light has to pass through a lot more air. This leads to the star’s light being extincted by the air masses, causing it to look dimmer. From Ireland, as late as the two stars remain visible, there are roughly 2 air masses dimming Rigel, closer to 1 and a half air masses for Betelgeuse. This is a factor of how high it is in the sky, and is one of the reasons why it would Betelgeuse may have appeared brighter, or was seen to be brighter, from sufficiently northern latitudes.

Speaking of being made to look dimmer, this of course happens to Betelgeuse as part of its variable nature. There are various traditional names for Betelgeuse from cultures all over the world. Some from the Native North Americans, or the First Nations of North America, in extreme North America and Canada in particular Betelgeuse was regarded as being brighter than Rigel. This is potentially because of its height in the sky and the prominence of its colour. There are stories about Betelgeuse from the far other side of the planet as well, down in Australia, where a native oral tradition references the flickering nature of Betelgeuse. The variations in Betelgeuse’s brightness may have been known even before telescopes.

Looking into Orion’s belt reveals that the three belt stars are bright blue stars. If we were to look even closer, we’d see that the three belt stars are actually multiple star system of two or more stars each. A few of these stars are classified as O-stars. O is a stellar classification for the biggest, hottest stars on the main sequence. Their blue colour is an indication of their temperature, and combined with their huge mass, they tend to burn intensely but for relatively short lengths of time. Betelgeuse was likely a blue O-type star in the past, around a million years ago or so. It is hard to tell exactly how long ago and exactly what type of star Betelgeuse was, as it has since become a red giant due to age.

Taking a close look at Betelgeuse through any normal telescope will reveal that it just looks like a star. It will look like a dot, even though we know it’s roughly a ball. Betelgeuse, isn’t quite as simple as a plain sphere. It’s difficult to draw an exact boundary where the star stops and space begins. This is broadly true for many stars, when discussing their magnetic field or sphere of influence. For Betelgeuse, it’s hard to tell exactly where it’s atmosphere ends as it sheds shells of plasma off of its surface. Stretching out from the atmosphere is gas and other material, old plasma that has erupted off the surface. This gas forms rings and shells around the star, with outer reaches stretching as far as the equivalent to Neptune’s orbit. Let’s say the center of Betelgeuse was where the center of the Sun is in our solar system. The photosphere, the hot, lower atmosphere of Betelgeuse, would range out to around Jupiter, not quite as far as Saturn. The photosphere is the region we normally see when looking at a star (not with our naked eyes of course). What we might call the surface of the star, the top of the convection zone, will be closer to the Earth or Mars in distance. The very outer most clouds of material that Betelgeuse has released, would reach out as far as the orbit of Neptune. As Betelgeuse is after getting old, it’s also after getting a little bit unstable. This means it’s not quite as easy to draw circle around Betelgeuse and say, “Inside here is the star, outside here is not the star.” The star’s atmosphere stretches into space and also gets heated up by the star, causing it to glow on its own. This contributes to the brightness of the star and makes it look bigger.

Taking a look at the distance to Betelgeuse, it’s almost 500 light years, give or take 56 light years. The error range here is another element of uncertainty. Not only is Betelgeuse a variable star, there’s no planets orbiting around Betelgeuse and it doesn’t have a large easily visible companion star orbiting close to it, making it hard to figure out things like Betelgeuse’s exact age and exact mass. If we don’t know exactly how far away something is, it can be hard to nail down any other details. Many astronomical calculations, for figuring out mass and size, depend on knowing distance or brightness with accuracy. An error range in those values gives and error range to any subsequent calculations.

It doesn’t look like Betelgeuse is going to blow up anytime soon. The inevitable explosion of Betelgeuse is often promised to be coming soon. It is a perennial feature of many newspapers and magazines, or website articles, to say that Betelgeuse is about to blow up, that Betelgeuse is going to pop this year or any day now. The variation in Betelgeuse brightness contributes to speculation, particularly when Betelgeuse dimmed and got much fainter around 2019-2020. It’s now believed that Betelgeuse shed more material off of its surface, and this cloud of material blowing way from Betelgeuse cooled and turned into dust. This essentially blocked out the light of the star, dimming it or extincting it the way our atmosphere extincts the brightness of stars. This variation is a typical feature of Betelgeuse and isn’t a sign that it’s going to blow up anytime soon. Thankfully, this means we can say its name as many times as we want, Betelgeuse, Betelgeuse, Betelgeuse or Beetlejuice, Beetlejuice, Beetlejuice, and nothing bad will happen.

As we’re finishing up, I will return to the morning of the 21st, the morning just after Culture Night, mostly to point out the planet Mercury. Mercury will definitely be visible in the countryside if you don’t have obstructions on the horizon. However, it will be more difficult to see from the city. Luckily a bright red star like Betelgeuse is going to be visible even in more like light polluted areas, even when it is at one of its more dim periods. Betelgeuse shouldn’t be too much fainter than the 20th brightest star in the sky and it’s usually closer to the 10th brightest star in the sky.

I hope you enjoyed this piece talking a little bit about Betelgeuse, I very much hope you enjoyed it. If you did enjoy, you can like this article and follow this website and my YouTube channel. Hopefully, I’ll see you back here for the next one.