Caoimhín's Content

Today we are going to be taking a look for a comet. The comet we’re going to take a look at is starting to be visible, it’s starting to come in towards the Sun and get closer towards the Earth, but it won’t reach its closest to us until we get into August. Nonetheless, we are going to take a look for it here.

We’re taking a look at the sky early enough in July, we’re coming up to local midnight at about 1:20 in the morning. That puts Scorpius low to the south-southwest. Antares is just visible over the horizon, tracking eastward would bring us to Sagittarius and then onto Capricornus and Aquarius off towards the southeast.. They are tougher to see constellations and we are looking at them from a city, we will stick with the light polluted sky for the moment. With the lines of the constellations to help us part of Scorpius is clearly visible, but most of it is under the horizon so it is tough to tell. The teapot shape of Sagittarius is pretty clear in the south and if you know what you’re looking for Capricornus and Aquarius are next. They are abstract and faint, but just a little bit higher in the sky we have the Summer Triangle, and a little bit to the east we have the square of Pegasus. Aquarius and Capricornus are just under the triangle and between the two shapes of Pegasus and Sagittarius. If we move forward a day or two, that will get the Moon out of the sky, but it is still difficult to see the constellations of Aquarius and Capricornus. The Summer Triangle of course is nice and easy, some of the brightest stars in the sky, but it’s tough to see the full square of Pegasus. The bottom star of the square is pretty faint and hard to see. Lower in sky is Saturn, but it’s so low that it is difficult to see in most conditions.

Looking in the direction of Capricornus er should be seeing the Comet 10P/Tempel. The information in stellarium is apparently for the epoch 2025 and it might be outdated, but we shouldn’t be too far wrong. The comet is just in the tail of Capricornus. As we move forward in time, it comes lower in Capricornus. As we move back in time, it goes back up into Aquarius. Even this early in July, we’ve already moved far enough forward to see it in Capricornus rather than Aquarius. The comet is just at magnitude 7.19, reduced to 7.64 by the air. because the comet is so low to the horizon. It would be easier to see from lower latitudes, lower on the planet, but it is up for us, and through binoculars it looks fuzzy, as a comet should.

The Tempel part of the comet name is after Wilhelm Tempel. Wilhelm Tempel was an astronomer who discovered 21 comets, including this comet and 55P/Tempel-Tuttle, the parent body of the Leonid meteor shower. The comet Swift-Tempel, Swift-Tempel-LINEAR, these are all discovered, or partly or jointly discovered, by Ernst Wilhelm Leberecht Tempel. To get a better look we’ll go all the way out into the countryside, free of light pollution. Still the comet is just beyond the edge of visibility, but from the countryside we do have more stars visible to the naked eye to help us find it. It definitely gives us a clearer view of Sagittarius and the Summer Triangle is still prominent. The Square of Pegasus looks more like a square, but due to the sort of abstract shapes involved, Aquarius and Capricornus are still difficult to spot, they’re tough constellations to recognize. The Comet 10P/Tempel is visible through binoculars, even through quite small binoculars. The comet is quite bright at 7.19, so just on the edge of visibility to the naked eye, it’s just barely out of unassisted view.

We’ve established where the comet is while it is still further from the Earth. It’s only 0.4 AU away even in mid July, less than half of an AU away. It’s still over an AU away from the Sun and because of when and where we’re seeing it it should be behind us relative to the Sun. We’re seeing it almost in the south, almost at midnight. Not exactly in the south, not exactly at midnight, but not too far off, which means it’s almost on the far side of the Earth to the Sun. That is reflected in the distances, he comet is over an AU from the Sun, but less than AU from the Earth. As we keep moving forward the distance comes down to just 0.414 AU, that’s about 61 million kilometers. The lowest it gets to is about 61.937 million kilometers and that brings its brightness up to 6.87. That is, from a dark sky, on the edge of visibility to the naked eye, just about visible. However, we’re after moving all the way through to early August, just after the Full Moon and the nearly Full Moon is in the sky. We would have to have move back earlier to get the Moon under the horizon and unfortunately, the comet goes under the horizon first. Once we get into August, once the comet is actually at its closest to us and at its brightest, the light of the Moon is going to interfere. By moving back in time a little bit we can get a compromise. At the end of July, July 23rd, the comet is still under 7th magnitude, so just about visible to the naked eye in a dark sky, but it is just barely visible.

If we zoom in a little, it’s pretty clearly visible and it has that fuzzy shape that we would expect of a comet. Taking a closer look around its perihelion, there is a degree of a tail. There’s at least a sort of shockwave in the comet’s coma indicating what direction the tail would be facing. As we get closer to the the perihelion, it gets down to just 1.417 AU from the Sun. This is a comet that always stays further from the Sun than the Earth is and due to that, it’s never going to be that bright. It’s never going to be as bright as comets that can get between the Earth and the Sun, where they are catching much more light and therefore look much brighter in the sky. We can see that does get up to 6.87 magnitude, which is pretty bright, but again, around the night of the Full Moon. It is difficult to see and not generating that much of a tail, but that is the Comet 10P/Tempel. That is really the best comet for us to see during July, it’s the one that’s going to get closest to us, but due to the light of the Full Moon, due to how low it is in the sky, it’s not a perfect view.

If we move down closer to the equator it will look better and we’ll be able to see it under darker conditions. From just barely south of the equator the comet looks much higher in the sky. We’ll move forward again to its closest position to the Earth, in early August, and we’ll see where it is in the sky. The Moon is under the horizon, the Sun is not yet peaking above the horizon and the comet is up. We’re right in the middle of the night and in a perfect dark sky so the conditions are perfect. It is a clearly recognizable dot to the naked eye, brighter than some of the other objects around it. Even though it is quite faint, it is a little bit fuzzy. If we take a closer look, the fuzzy shape is even more obvious, making it clear that this is a comet. We’re seeing it there at 6.87, reduced to 7.15 due to how low it is in the sky, but it’s not particularly low in the sky, it is fairly high in the east. We can get it a little bit higher before the Moon comes into the sky or before the Moon really contributes, so that brings it to about 7th magnitude.

From closer to the equator, that’s a pretty ideal viewing condition. We’ll go in between, we’ll come to Southern Europe, much further south than us here in Ireland, but further from the equator than the last view. From here, all of Scorpius and Sagittarius are very clear as well, all of this tells me that the comet should get fairly high in the sky. It does get higher in the sky from here than it would from Ireland, but due to the angle of the ecliptic, it’s still quite low while the Moon is under the horizon. We can get it to a higher position than it would ever be seen from here in Ireland, but that is with the just past Full Moon in the sky, so that is going to make things more difficult. With the Moon under the horizon, we can see that it’s almost magnitude 8, so really out of view to the naked eye, but still achievable to binoculars.

Without a doubt, this is a better target for binoculars or a telescope than the naked eye. For us here in Ireland at least, it may be easier or better to take a look at this comet before it reaches its closest position to the Earth, because it will be higher in the sky and the Moon will be out of the way. As we move forward, even though it comes closer to us, it sinks lower in the sky, and that actually makes it look fainter because of the extra air in the way, because of the curved sphere of atmosphere around the Earth. The fact that the atmosphere curves around us means that it is thicker at the horizon, we’re looking through it at a steeper angle,

That is 10P/Tempel, the comet that is closest to us in July and August. Even though it is going to get closer to us in August, you may want to take a look at it in July, and I hope that you’ve enjoyed this piece taking a look at it. If you enjoyed this piece, then please do like it. If you enjoy 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.