Caoimhín's Content

Today, we are going to hop into the past, but we’re not going to go particularly distantly into the past. Going into the past isn’t something that I regularly do on this channel, but it is something that we have done before and I may do more regularly, there are some interesting things that have happened in the past.

The one I am looking for in particular today is a particular comet, Comet 1P/Halley. Comet 1P/Halley is one of the most famous comets ever to have come through the solar system, it’s one of the best known comets and it is Comet 1P/Halley, it’s the first periodical comet to ever have been discovered. We’re going back to the year 1986, which is the last time Comet 1P/Halley was close to the Sun. It doesn’t look like it was in a great position to be seen from here in Ireland when it was close to perihelion, so we’ll have to move away from that extreme a little bit.

I’ve spoken a lot about comets recently, now, particularly with the interstellar comet coming through the solar system, but none of the more recent ones are as impressive as Halley’s was in 1986. In the Stellarium software I use, thanks to some sort of glitch, there are two separate options for Halley’s Comet, two visible comets, both pointing in slightly different directions. They’re both Comet 1P/Halley, they’re both displaying the same information. The orbit of the comet can be based on different estimates and in this case these two estimates have gone a little bit out of sync here. The two versions of Comet 1P/Halley are going around the Sun on slightly different paths, rather than one simply being a copy of the other, because their positions relative to each other are changing. As they come closer to the Sun their brightness increases and they start developing tails. This is something that I wanted to check because some of the comets that we talked about recently did not show any tails in Stellarium. These various versions of Comet Halley are showing plenty of tail, which is really what we want to see when we take a look at a comet.

The interstellar comet 3I/ATLAS seems to have lost its tail. It seemed to have a little bit of a tail for a while, but then that tail seems to have stopped being produced. Of course, Comet 3I/ATLAS comes from a different solar system, so there is the possibility that its composition is different to the comets that we’re used to seeing in our solar system. Comets in our solar system are going to be composed of the same stuff that the rest of our solar system is composed of.

Moving past perihelion, the comets lose their tails again. Comet 1P/Halley is a particularly spectacular comet. It’s one of the comets that’s visible to the naked eye, which is one of the reasons that that it’s so popular. One of the reasons it’s so well known is because it’s visible to the naked eye, people have been able to see Comet 1P/Halley since long before the invention of telescopes and binoculars. Comet 1P/Halley has been visible and known since ancient times, simply because people have been able to see it since ancient times. Of course, for most history, people didn’t know it was the same comet coming around over and over again. The tail of the comet appears a little bit further from the Sun than I would expect, but increases to a peak around perihelion. Then they stretch out the other side before fading away. The tails are certainly visible when the atmosphere and the ground are taken away. Even with those brought back, it is visible to the naked eye just about. Even pretty close to the Sun in the sky, with the glow of sunset interfering, but still visible. Of course, they look a little bit different in simulation to how they look in the real sky, mostly because there’s two of them. All the same, it’s clearly visible here to the naked eye, very similar to how the stars or the planets would be visible. It would be visible growing that tail over time.

That is Halley’s Comet. Halley’s Comet comes around pretty rarely, every 70-odd years, and we have already taken a look into the future to see the comet come back around in the 2060s. However when we looked at the future Halley’s Comet, it didn’t produce a tail. Looking at Halley’s Comet in the past, the last time it came around in 1986, the tail is being displayed. The last time it came into the solar system it was very thoroughly observed, so this does lead me to believe that there might be some issue with Stellarium showing the tails of these things if their orbital parameters aren’t fully known or fully understood.

We will continue looking back in time, but much less far, we’re just looking back at 2023. There is a much shorter period comet that I’ve also mentioned recently, Comet 2P/Encke. Comet 2P/Encke is one of the shortest period comets, so it comes through the solar system every three or so years, but it doesn’t seem like the most recent pass is in Stellarium. It’s showing the orbit based on the 1961 pass, even though the comet was at perihelion in 2023 as well. It will come through the inner solar system again in just 2027 because the period of this comet is so short. Unfortunately, using the orbital elements for the epoch 1961 and looking at it for 2023, we’re not seeing a tail in Stellarium. It’s only magnitude 8, brighter than most of the comets were able to actually see in the sky at the moment like Comet F2 and R2/SWAN and Comet A6 Lemmon.

Just to be fair to the comet, we’ll go back to 1961, even further into the past than our viewing of Halley’s comet. We will do the same thing, we’ll get rid of the ground, we’ll watch this comet make its closest approach to the Sun and then we’ll see if it develops a tail, which we would expect, especially if we’re looking at the comet for the time period that the data was collected. We’re starting reasonably far from the Sun, 3 AU from the Sun, and because Comet 2P/Encke isn’t yet particularly close to the Sun, there is a chance that it hasn’t picked up a tail. Moving forward we’re still getting closer and closer to the Sun, hopefully the comet will get close enough to the Sun for a tail to be generated. If a comet doesn’t get close enough to a star, then there’s not going to be enough heat for the tail to be created. The tail of a comet is really the comet losing material as material melts from the heat of the Sun and gets blasted out into space by the Sun’s solar wind. It looks like we reach a low point, the lowest number and our closest position to the Sun, at just about 0.339 AU, one-third our distance to the Sun, give or take. It’s only showing a very faint tail, but it is magnitude 6, just about what’s visible to the naked eye.

Of course, from here in Ireland, we would have seen it very close to the horizon, it would be very difficult for us to see this comet. In order to give a better view, we’ll go very close to the equator. We will bring back the ground and the atmosphere and we’ll get the comet just above the horizon. This puts the comet just above the sunrise, but still visible. With Comet 2P/Encke, unfortunately, it doesn’t look like we’re going to get a good simulated view of it in 2023 or 2027, simply because that version of the comet isn’t updated, but it was there, just above the horizon, in the 1960s.

Comet 1P/Halley is the big, famous one, and it’s famous for having a big, impressive tail, so I’m glad that the tail actually comes up and the Stellarium software shows what the comet is likely to have looked like, even though when we look forward to the 2060s, we couldn’t see it. Unfortunately, it looks like Comet 2P/Encke isn’t showing much of a tail in Stellarium, but for that one, we don’t have to wait too long, we’re only going to have to wait until 2027 before it makes its next closest approach into the inner solar system. I usually pronounce “Encke” as if it was “Enk” but it really should be closer to “Enki” or “Enky”

I’ve been talking a lot about comets recently, so I thought I’d give some historical examples, some examples of comets that I was more confident would be visually impressive, and thankfully, both of the versions of Halley’s Comet were. I hope that you enjoyed this piece, if you did then please do like it. If you like this kind of content, then please subscribe to this website and my YouTube channel. Thank you very much for reading and hopefully I’ll see you back here next time.