Caoimhín's Content

In several recent pieces we have taken a look at a few different comets and a lot of them were discovered just this year. For example, Comet 3I/ATLAS, which is an interstellar comet, it’s full name is 2025 3I/ATLAS, it was only discovered this year. In order to take a look at this comet in Stellarium, I had to add it into Stellarium because it is so newly discovered. The same is true for a bunch of the other comets that we took a look at, such as Comet Lemmon and Comet R2/SWAN.

I don’t think I’ve mentioned Comet R2/SWAN in a piece before, but it is up in the south at the moment. Comet Swan, in mid to late October, is magnitude 9.99, so it is a brighter than Comet Lemmon back on the other side of the sky. Comet R2/SWAN is just one of the SWAN comets discovered this year, another is Comet F2/SWAN. They were both discovered by the Solar Wind ANisotropies instrument on the SOHO satellite, the Solar Orbiter Heliosphere Observer, an ESA satellite. Although Comet 2025 F2/SWAN was also discovered this year, it is already in Stellarium, so we can find it without loading it in as a new object. According to what I’m seeing, it never rises for us in the Northern Hemisphere, unlike R2/SWAN. A lot of comets have been discovered by SWAN and these comets are discovered when they’re very close to the Sun because that’s where the Solar Orbiter Heliosphere Observer, the SOHO satellite, is looking. It’s always looking towards the Sun, as that is what it is aiming to study, but it also catches comets coming from behind the Sun.

Occasionally with these newly discovered objects, they need to be added into Stellarium, Stellarium might not necessarily already have them. For example, I couldn’t find a particular asteroid discovered this year, which is good if anything, because it gives me a chance to add it in. The object in question is the asteroid 2025 PN7. Stellarium doesn’t already have this asteroid as an object, but it does have an official Minor Planet Centre designation, it’s official name. By going to the configuration window of Stellarium, there is a Plugin section. The Solar System Editor is one of the Plugins, and it needs to be selected to load once the program starts, so you might need to restart the software. Once it’s running, you click the Configure button. This will open a window with a list of objects and an option to import an object in MPC format. That’s the option we want, which opens another window with two tabs. The second tab is a search tab where you search for the object you want. Once it comes up, select it and it will load into Stellarium. I went through this in a previous piece, but I also had to do it for more recent pieces discussing the comets. I had to add some of the comets I was discussing, but I didn’t mention it, I just did it in the background as it were.

PN7 isn’t quite the right name, it’s really PN₇ with a subscript. The naming system for these asteroids, the provisional designations they receive, they’re reasonably similar to the way that we name comets. You might recall from a recent piece, that when we’re naming comets they get a letter for the half month that they’re in. This is for normal comets, not for interstellar objects like 3I/ATLAS. The comets, for example, F2/SWAN and R2/SWAN, they were discovered in March and September, March for F and then September for R. Those were the half months that they were discovered in, so F for second half of March and R is the first half of September. With asteroids, the first letter works the same way, but the second is a little different.

We’re going to head out to the countryside just to make this asteroid a little bit easier to see. It’s currently at about magnitude 25, so it’s a very faint object. There are a lot of these tiny rocks out in space so of course, establishing all of the provisional designations for them requires a system. For this asteroid, P means it was discovered in the first half of August. N and 7 represent how many of these have been discovered in that half month. The first asteroid discovered gets A. Let’s say the first asteroid discovered in January, that would be AA, and then you go through the alphabet, AB for the next asteroid and AC for the one after that, and so on. Once you run out of letters in the alphabet, once you get all the way to Z, you start all over again, minus a letters. You go through 25 letters of the alphabet because you’re not doing “I”. “I” is left out because it looks too much like 1. So this particular asteroid, PN7, we had to go through the alphabet seven times. Seven times 25 is 175, and N is the 13th letter of the alphabet, so 188. This was the 188th asteroid discovered in the first half of August, in 2025.

A lot of asteroids get discovered, what makes this one interesting is its orbit. We’re going to head out to the solar system observer and we’re going to try to observe the orbit of this particular asteroid and take a look at it from above. It’s a particular type of asteroid, an Arjuna asteroid, which occupies an orbit that’s similar to the Earth’s, it’s an Earth-like orbit. The asteroid seems to be too small and new for an orbit line to be drawn by Stellarium. That, or it’s orbit is too chaotic in the long term. Luckily, the object is close enough to the Earth that both can be seen together orbiting the Sun. By moving through time, we can see that the asteroid is staying pretty close to the Earth, in fact it almost looks like it’s orbiting the Earth. This is a quasi-satellite. It’s not really orbiting the Earth properly, not like our Moon, it’s not going to stay orbiting the Earth, but it is with us for now.

If we go through enough time simulated here, eventually it will escape Earth’s gravity, it will still orbit the Sun a reasonably similar distance from the Sun as the Earth, but not necessarily near the Earth. It’s still in an orbit that’s going to be similar to ours, but just for the next little while, up to the 2080’s. It looks, in Stellarium, that the asteroid stops truly orbiting the Earth by the 2040’s, but is still co-orbital with the Earth. It goes into a slightly different kind of orbit, approaching close to the Earth and then slowing down and pulling away again, which is a different kind of quasi-satellite orbit. If we go back in time again, closer to the present day, even though the orbit isn’t outlined, it’s still clear that it is looping around the Earth, the Earth is pretty much included in its orbit. This is an asteroid that is going to be a reasonably close companion of the Earth’s for decades. It’s not the only one, there are other quasi-satellites, asteroids that have an orbit similar to the Earth but aren’t necessarily bound by the Earth’s gravity. They’re really orbiting the Sun, but they are influenced by our gravity, usually only over short periods of time. Some asteroids stay with us for longer, but don’t necessarily go around us. Of course, 2025 PN7 was only discovered this year and it’s one of many asteroids that were discovered just in this particular half month.

There is another object from 2014, which Stellarium doesn’t seem to have. It’s another object to add in the exact same way we already did, using the Solar System Editor plugin, and importing an element in by searching its Minor Planet Centre designation. The object we’re looking for is 2014 OL339 or OL₃₃₉, which is quite a big number and it works the exact same way as the other example. O is for the second half of July, L is the eleventh letter of the alphabet, and for this particular half month in 2014 we needed to go through the alphabet 339 times minus the letter I. I used a calculator for this one, 25 times 339 is 8,475 and with L being the 11th letter of the alphabet, that goes up to 8,486. This is the 8,486th asteroid discovered just in the second half of July in 2014. It’s another quasi-moon, similar to this new asteroid 2025 PN7. Unfortunately, it doesn’t seem to have imported, at least not for 2025. I might be able to see it if we go back to 2014, but that would be an issue for another day. 2014 OL339 is just an example of how high the number of asteroids can get, even splitting them up into just half months. Often you need to go through the entire alphabet hundreds of times if thousands of objects are discovered.

So that’s a little bit about adding an object and this newly discovered object, our temporary satellite, which is very difficult to see, but it’s going to be reasonably close to the Earth for a few years now at least. I hope you enjoyed this piece, if you did, please do like it. If you enjoy this kind of content then make sure you subscribe to this website and my YouTube channel. Thank you very much for reading and hopefully I’ll see you back here next time.