Caoimhín's Content

There has been a lot of hype in the news lately about an upcoming nova, an appropriate amount of hype given what is going to occur. Both novae and supernovae get there name from the Latin word for new, nova, as they can appear to form a whole new star in the sky. This is because they get brighter, they go from invisible to the naked eye to visible, their magnitude increases. We have talked before on this channel about supernovas and what will happen to a star like our Sun at the end of it s life, which isn’t any kind of nova, but we will go over some of the details here. We begin by looking at the mid April sky from a city at around midnight. This nova is expected to occur by September, and we know this because it has happened before. Some novae can occur over and over again, recurrent nova, like this one. Supernovae don’t generally reoccur.

Supernovae are commonly caused by a star exploding at the end of its life. When this happens, of course it can really only happen one time, once the star explodes it’s done. Some supernovae can happen after a star explodes, if its old core is able to build up enough new material, but usually a supernova is the massive release of energy when a huge star, much larger than our Sun collapses. A white dwarf building up enough material for to brighten like a supernova is a type 1a supernova, all the other types are cause by the collapse of a stars core. By looking in towards the summer triangle, in towards Lyra, we can find the Ring Nebula. The Ring Nebula is invisible without a telescope and it is easier to spot in the countryside. The Ring Nebula is a planetary nebula, the remains of a smaller star like our Sun reaching the end of its life. Even stars up to about 7 or 8 times bigger than our Sun will fall apart in a comparatively peaceful way. When these smaller stars reach the end of their lives they swell up into red giants, even our yellow dwarf Sun will turn into a red giant, and its outer layer will eventually get blown away as the inner part of the star starts to fuse different elements and become a little unstable. This blown out cloud of material is what creates the ring shaped nebula.

Only the most massive stars have a heavy enough outer layer for it to collapse back in, increasing the pressure and causing the classic bright core collapse of most supernovae. In the constellation of Cassiopeia there is a Supernova Remnant called Cassiopeia A. It looks nice and messy, not the even ring of a planetary nebula, but a messy shell of elements mixed together. Looking for Cass A can be tricky, as we are looking into the Milky Way there are a lot of things in Cassiopeia. Luckily Stellarium has a search function which certainly helps finding objects like Cassiopeia A. Taking a closer look at this Supernova Remnant, you can see all of the colours of different elements being blown away from the old center. When stars that are much more massive than our Sun, more than 8 times more massive, 10 or 20 times more massive or even more, the outer layer that’s been puffed up as the star ages into a red giant collapses back in and that collapse fuses new elements together, and the energy this releases is the explosion that blows all of this material into space. This also generates a lot of light, supernovas are brighter than a nova, they are a “super” nova. Both a supernova and a nova are just two occasions when something in the sky gets brighter.

Looking towards the south at midnight we’re able to see quite a few stars, even with the Moon in the sky, even from a city with some light pollution. The stars that we can see in the city are the ones that are of a high enough magnitude to be visible through the light pollution, the ones that are bright enough. On the magnitude scale, the brightest stars have the smallest number. Looking at the star Procyon, the brightest star in Canis Minor, which is in the selected view of the sky, it has a magnitude of 0.4, very very close to 0 which makes it quite a bright star. A little earlier in the evening the brightest star in the night sky, Sirius, will be in the sky. Sirius is definitely brighter than Procyon, Sirius has a negative magnitude, minus 1.45. This means it is brighter than the zero point of the scale. The smaller the number, or the bigger the negative number, lower the number is on the number line, the brighter the object is going to appear. If we look at the Moon, its magnitude is minus 9 , so that is a very very low number, a big negative number and that indicates that it is a very very bright object, much brighter than Sirius.

We’re going to be looking for a new star appearing in the constellation of Corona Borealis. Corona meaning the crown, just like the crown of the Sun, the corona that we get to see during an eclipse. I hope some of you got to see the recent solar eclipse, the total solar eclipse, that was visible across North America on the 8th of April. Corona Borealis is a constellation that we mostly see here in the North that’s why it’s Borealis, up here on the boreal side, we have the Aurora Borealis and down South they have the Aurora Australis. The constellation Corona Borealis is a pretty faint one, it’s tough to see especially from here in the city. Luckily, there are some little tricks you can use when we’re looking for it in the sky. We’ll start by finding the Plough. You can either turn around to the North or lean back and look straight up into the sky. The Plough or the Big Dipper is nice and high in the sky, close to the zenith in April and it’ll stay nice and high close to midnight for another few weeks. The handle of the Plough or Big Dipper has a curve to it, an arc, if you follow that arc you will arc to Arcturus. Arcturus is a nice bright star, one of the birghtest in the sky. It’s magnitude is even lower than Procyon, at just 0.15. Arcturus is nice and clear, nice and bright in the sky, it’s part of the constellation Bootes. This is a bit of a tricky name, you have to pronounce those two O’s separately, and it is often spelt Boötes to show that the sounds are separate, or in hiatus, like the word cooccur, or co-occur or coöccur.

If we find Arcturus, which isn’t too hard, it is a very bright star even if it isn’t in a very famous constellation, we can use it to find other stars. Arcturus is pretty much level with Leo over here at this time of the night and year, and Leo leads down into Virgo with the bright star Spica, Spica being the brightest star in Virgo. If you use the handle of the Plough to arc to Arcturus, you can spike on to Spica, and that will help you find that bright star. The brightest star in the constellation Corona Borealis is Alphecca If you have arced to Arcturus, just to its left, or East, almost right under the Plough is Alphecca. If you drew a line through the Plough and came down pretty much level with Arcturus, little lower, that will bring you into the right location to find Alphecca and Corona Borealis. Further East we have Vega, a very bright star, it is magnitude 0. Anything brighter than Vega gets negative number anything fainter than Vega gets a bigger number. In Corona Borealis, Alphecca has a magnitude of 2.2, not incredibly bright, but a magnitude of 2 is reasonably bright. A good comparison is Polaris, the North Star. Polaris has a magnitude pretty close to 2, a little brighter than Alphecca, they are both reasonably bright stars.

Find the star Arcturus, go left or East until you’re looking straight under The Plough next to Arcturus, a bit closer to Arcturus than Vega, and the star you will see, about as bright as the North Star, in the city that is the only star you can see in Corona Borealis. All the other stars in the constellation aren’t even visible from here in the city, because their magnitude is too low. In a dark sky out into the countryside without the light pollution, we can see the kind of curved shape of Corona Borealis. It is supposed to look like a crown, and with the lines of the constellations to help, you can see that all of the stars of Corona Borealis are definitely visible in the countryside.

There is a collection of pretty bright stars, Spica in Virgo, Arcturus in Bootes and Vega in Lyra, with the brightest star in Corona Borealis, Alphecca is a bit fainter in the middle of them all. The exact star that we’re looking for is T Coronae Borealis and it is a star that is quite faint, fainter than anything we can see with the naked eye. Also known as the Blaze Star, it is normally about 10 on the magnitude scale, also referred to as 10th magnitude. It is invisible to the naked eye even in the countryside, again the search function in Stellarium is useful. It may be visible through binoculars in very dark skies, but usually a telescope is required to see it. That is, until it brightens up to about magnitude 2, or 2nd magnitude. That will not only make it visible to the naked eye in the countryside, even in the city we will be able to see it. If you can see the North Star, that is about how bright it will be, appearing in the otherwise empty patch of sky just East of Alphecca. A recurrent nova like this one, and indeed most novae, happen only with double stars. You need to have a big massive red giant or a similar massive old star, with a small white dwarf orbiting around it. If a white dwarf gets close enough to its massive partner, it will pull over extra material, sucking in the diffuse hydrogen and helium atmosphere of the bigger star. The extra material siphoned off will build up around the smaller companion. This leads to more and more hydrogen and helium building up around the white dwarf, until there is enough for it to fuse. Suddenly, there will be a huge rush of nuclear fusion, producing a load of extra light. The fusion will burn through that extra material, and the star will fade. Then you’ll have to wait for it to build back up again before the nova recurs. There are only a handful of recurrent novae that we get to see regularly, ones that happen in our Milky Way, luckily there are other nova that happen less regularly. There is a theory that all novae are recurrent, unless they actually blow the star apart, it’s just that they take a very long time to repeat, 10,000 or even 100,000 years. Novae like this one recur a little bit more regularly, it has observed brightening up in modern times. Before it brightened up the last time, it dimmed. The white dwarf builds up a disk of material around it which can make it it look fainter, until that material ignites in the nova. At the moment the smaller white dwarf companion is dimming, we’re seeing the same kind of dimming that was observed last time. This gives us a good indication that it is about to brighten up again. Hopefully by around September we’ll get to see this nova happening.

Novae are hard to predict so it is over the course of the next couple of months that the nova should occur, figuring out the exact date is almost impossible with our current knowledge. These nova are often visible for days at a time, so you are unlikely to miss it, especially now that you know the right place to look and how to find it. I will most likely mention it again as it is happening or just after it happens, so keep an eye out for updates. You can subscribe both to this website and to my YouTube channel if you’d like to be kept up-to-date about this and other extraordinary astronomical events, as well as more ordinary ones. I hope you enjoyed reading this article and found it edifying, hopefully I’ll see you back here for the next one.