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Today, we’re starting by looking at the sky for October 21st. We’re looking at the sky reasonably late, just before midnight. We’re looking at the 21st because we are taking a look for the Orionid meteor shower, and they peak on October 21st. This meteor shower have got a maximum Zenith Hourly Rate of about 20, but being in Orion and lower in the sky for us than our zenith, it’s showing local zenith rate of about 18. I hope some of you get the chance to travel into the countryside where, of course, your view will be much, much better.

By moving through time, we can see that the amount of meteors we’re getting goes down as we move later in the night. The rate is also reasonably high on the morning of the 21st, this morning, as well. The local zenith rate goes from 18 up to 19 or 20 during the day for us here in Ireland. The rate is still 19 just as the Sun is setting. However, the radiant is below the horizon, we’re probably going to see a lot less, and that’s indicated by the actual local rate, which is also brought down by the light pollution of the city. As the radiant comes more into the sky we should start seeing more and it’ll be at its best roughly when the radiant is at its highest, which is around 5:30 in the morning of the 22nd. All in all, the Orionid meteor shower is reasonably good, it’s quite a productive meteor shower. It is best seen from the countryside as light pollution will interfere, but it is something that pops up every year, so if you don’t get to see it this year it will come back around.

I mentioned in the past couple of pieces, where I talked about the Orionids and the October sky generally, that these meteor showers are essentially created by comets. For example, taking a look at the Southern Taurids and the Northern Taurids as well, their parent body is Comet 2P/Encke, the second periodical comet that was ever discovered. While that comet comes through the inner solar system, it leaves behind a trail of dust and gas. As it crosses the Earth’s orbit, the Earth ends up moving through that trail of dust and gas. For the Northern Taurids we do so around the 12th of November, so their peak is still coming up, and for the Southern Taurids, it’s the 10th of October, so their peak has passed. The trail of dust and gas left by the comets is what provides all of the little bits of dust and rock that fall through our atmosphere and burn up as meteors. The meteor shower is really little bits of comet left across our path and then lighting up in our atmosphere. In Stellarium, the parent body doesn’t seem to be listed for the Orionids, but I can tell you that it is Comet 1P/Halley. Halley’s comet is probably the most famous comet ever, because it was the first that was confirmed to be periodical and it is described or mentioned in various old texts, such as ancient documents about the night sky. It’s preserved in tapestries and pictures from all over the world as well, because it’s been coming through the solar system regularly for hundreds and hundreds of years at least, most likely centuries or more.

Unfortunately, it doesn’t come by very frequently, only every 70-odd years or so. The comet does have a variable length to its orbit, from around 70 to 80 years, but it usually comes around every 75 to 77 years or so. Looking for Halley’s comet at the moment, it’s currently pretty far away about 35 AU from us. The Comet last came by in 1986 and it’s full name is 1P/Halley (1986). It has other designations that feature the year 1982 instead, as this is when it was seen coming back into the inner solar system. 1986 is the last time that it came back around, so we’ll need to go forward quite far for it to come back around. If we come forward to the 2060s, the comet is going to come back into the solar system. By jumping from 2025 to 2062, the comet drops to only 1.35 AU away from us. From 35 AU, that’s a difference of 34 times the Earth’s distance to the Sun. We’re still looking in October of course because we were looking at the Orionids and they peak in October. The comet is still 2 AU away from the Sun. By moving forward and backward through time, it’s brightness increases as we move forward, meaning it’s still on it’s way into the Sun. However, according to other sources, Halley’s Comet will reach its closest on the 28th of July 2061. There is a good chance that Stellarium is the incorrect one, as it is using information from the 1986 epoch to track the comet. This is something I may fix in a future video.

By continuing to move ahead with the increasing brightness of the comet, we’ll have to change the time of the night that we’re looking at in order to keep it in view. The comet seems to get up to magnitude 4 while it’s still dark, just after sunset, already bright enough to be seen in the city. As the comet gets closer to the Sun, it becomes more difficult to see, but the magnitude climbs to 2. It’s still up to magnitude 3 when it comes back around into morning time. In Stellarium, this moves us into 2062, showing the comet’s closest point to the Sun around February and visible again around the 1st of March. Based on other sources, the closest point to the Sun should be July 2061 and around August or September for it to return to the morning sky. Either way, once it comes around into the morning sky, it may get closer to us, but it may not get brighter than that. Often, the brightest point is when the comet is at its closest point to the Sun, and that’s usually going to be difficult to see from the Earth. It doesn’t look like it’s producing a tail but that is likely to be a limitation in the Stellarium software itself. This comet is the parent body of the Orionids.

We are going to shift our perspective out to the Solar System Observer, to look at the solar system from above. We have done this in a couple of pieces recently and will do so in another future piece soon. From here, we can see where the orbits of the comet and the Earth intersect. Stellarium allows orbits to be highlights, but it doesn’t look like Comet Halley is getting a highlighted orbit, possibly due to the older position information. Thanks to the crosshairs Stellarium uses to highlight selected object we can still follow where it is. We can still turn on an orbit line for the Earth, so that means we can see where it is and roughly when it crosses the Earth’s orbit. Pulling back in time to when the comet was still coming into the solar system, the comet is moving pretty quickly by the time it’s crossing the Earth’s orbit on the way into the inner solar system. It passes Venus and then heads on to make its closest approach to the Sun, pretty much crossing the orbit of Mercury. It just about comes closer to the Sun than Mercury before moving away, recrossing the orbit of Venus, and then crossing the orbit of the Earth again as well. The comet crosses the Earth’s orbit a bit ahead of the Earth on the way out.

By marking where the comet crosses the orbit and then moving forward until the Earth meets that mark lets us see when the Earth would be moving through the comets stream, roughly. In this case the Earth comes around to that point quite early in the year, around May. The dates here are likely a little off, but this seems to be very far from an expected October date, to provide the Orionids. Luckily, that is only one of the crossings, Halley’s Comet will cross the Earth’s orbit in two locations. By coming back in time we can check where the comet crosses on its way into the Sun. The comet crosses the Earth’s orbit behind us, while we’re ahead in December. The difference is only a small portion of the year, we can tell because it’s only a small portion of the orbit. Doing the same thing, marking the crossing point, but now moving back in time, the Earth comes back around to that crossing point at the start of November. This is just a few days off the expected 21st-22nd of October to coincide with the Orionid peak, but it is close enough when the perihelion also seems to be a little off. This isn’t the most accurate measurement technique ever, so I’ll give myself some benefit of the doubt.

Looking at the solar system just from above, as if it was a 2D plane, the comet comes in through the inner solar system and crosses the orbit of the Earth twice. There is a chance that due to the inclination of the comet’s orbit, there is a chance that the path of the comet is actually only crossing the Earth’s orbit on the way in, and potentially going over or under the Earth’s orbit when it is leaving the solar system. That is something that can happen with comets and it is unfortunate that we can’t see its orbit like that in Stellarium. Keeping the orbits of the planets highlight, we can zoom out and come back to the present day to get a better idea of where the comet currently is in relation to the rest of the solar system. In 2025, the comet is just outside the orbit of Uranus, but still inside the orbit of Neptune. The comet should have reached its aphelion back in 2023, so it has already started to come back inwards. It is of course going to take almost 40 years to travel from outside Uranus back in to the Sun. It is going to take a long time for it to make its way back into the inner solar system, so reasonably large timescales of decades are necessary, just to get it moving quickly enough while it’s far from the Sun. However, it moves much slower far from the Sun and then very quickly once it’s into the inner solar system, flying through in just about a year. The comets can be quite slow moving at their aphelion but they then speed up quite a lot at their perihelion.

That’s a little on Comet 1P/Halley, the progenitor, the parent body of the Orionid meteor shower which we can enjoy tonight, and also next year and every year in late October. I hope you enjoyed this piece taking a look at the meteor shower and the comet and how they relate to each other. If you did enjoy this piece then please do like it, and 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.