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Today we are going to begin by looking back to the Leonid meteor shower which happened, which peaked just a couple of days ago. To see the radiant of this meteor shower nice and high, we need the constellation Leo to be up, which it is now at about 3 o’clock in the morning.

With the meteor shower radiants displayed, the radiant of the Leonids is right in the sickle of Leo. Stellarium shows a variable zenith hourly rate of 5 to 20, and it’s showing the peak as being back on the 17th of November. I already mentioned the Leonids when we were looking forward to this time of the month rather than looking back. Like last time, their zenith hourly rate was a little bit higher when they rose after midnight on the 17th, morning of the 18th for us, than before they rose on the 17th, morning of the 17th just after the 16th. When saying exactly what date these things are peaking on, you do have to be very sensitive to when midnight was and what time of the night it is. The higher rate here is 3 to 14. I hope that the Leonids were good this year for anyone who caught them, we were expecting around a 15 to 20 rate. However, as I mentioned the Leonids are also the meteor shower that causes the very famous meteor storms, when the zenith hourly rate can be hundreds of thousands.

Taking a closer look at the radiant, you wouldn’t really see anything, it’s just where the Leonids come from. This radiant is not a fixed point in the sky. Although the radiant is passing through Leo, and it stays in Leo, it is moving around. It’s location in Leo drifts over time, and that’s because this is a stream of material in our solar system. Just like the planets in our solar system, they’re so much closer to us that our motion around the Sun changes their location in the sky as it appears with the background stars. The antihelion also moves, but a little differently. The antihelion doesn’t have a parent body because the antihelion is part of the constant background rate of meteors that we get in the sky. It’s more of a fixed feature, it’s some of the meteors that the Earth’s gravity pulls in as we go around the Sun. Whereas, the other meteor showers, they come from streams of material that were left behind by comets. Mostly comets, occasionally comets and asteroids, but usually it’s comets. The parent body of the Leonids is Comet 55P/Tempel-Tuttle.

Comet 55P Tempel-Tuttle is a shorter period comet. Not quite as short as Comet 2P/Encke at just 3 or so years, as we covered in a recent piece, but it’s still a lot more regular than longer, but still short period comets like Halley’s Comet. Halley’s Comet has a period 80, 70-odd, years long. Long period comets are those comets whose periods are multiple hundreds of years. Comet 55P/Tempel-Tuttle has a period of 33 years, making it fairly regular as comets go. In Stellarium, similar to 2P/Encke coming up as P/Encke, this comet comes up as P/Tempel-Tuttle. It’s easier to find in the List tab under comets. Several comets come up with this name, with years in brackets after them. These are different years when it had a close approach, and these years have slightly different calculated orbits. Using out of date parameters is part of why comets like Halley’s don’t show their classic tails if you use 1986 data for its 2061 visit. Stellarium isn’t showing data for the most recent one, which was in 1998. Of course, it also isn’t showing the next one which is going to be in 2031, because there is about a 33 year period to this comet.

1998 is the year that it came to perihelion last. As the comet comes to it’s closest to the Sun, it reaches a low point of 0.982 AU. This is just closer to the Sun than our orbit, however it’s also 1.816 AU from the Earth, so it is almost on the opposite side of the Earth to the Sun when it comes to perihelion. Different comets will come to perihelion at different locations in the sky, some even between the Earth and the Sun. Around perihelion, it seems to be magnitude 10, which is odd as it seemed to be a little brighter further from perihelion. This may be a glitch due to the 1965 data being used, but it might have something to do with its relative position as a conjunction may appear brighter. It gets down to around magnitude 9, brighter than Comet 3I/ATLAS and some of the other objects that we’re seeing at the moment. We’re not getting much detail in the comet either, likely because of the fact that we’re looking at it in 1998 when this estimation comes from its orbit in 1965.

Looking at 1965, Stellarium’s warning that the estimation has gone out of date is gone. Moving to the right time of the year and it looks like a very similar perihelion. The angle of the ecliptic is atrocious for seeing the comet from Ireland, so looking at this from a different location would be better. Instead, I’ll just get rid of the ground so that it isn’t in the way. We’re still seeing it at about magnitude 10, and it comes up to its closest point at just about 0.982 AU. It’s getting up to its closest position to the Sun pretty much on the opposite side of the Sun to the Earth again. If we view this closer to the equator, that would put the comet higher in the sky, higher off of the ground, as the Sun set. This would make it easier to see, as it would be in the sky as it got dark. Even then, at perihelion it still appears too close to the Sun in the sky, so it looks like this particular comet would have been a tricky one to see. It is much fainter when it’s further from the Sun and higher in the sky, in a position where it would be more feasibly visible. However, the view from around the equator in 1965 wouldn’t have been a terrible view of it.

That’s Comet Tempel-Tuttle from the Earth, the parent body of the Leonid meteor shower. We’ll come back to the modern day, back to the peak of the Leonids, and we will head out to the solar system observer. We’re going to head out to the simulated solar system observer point provided by Stellarium, so that we can look down on this comet from above and hopefully demonstrate one of the really interesting things about this comet, besides the fact that it provides the Leonids for us. It not only is an interesting fact about the comet, but it tells us a little bit about the Leonids or explains something about the Leonids to us as well. With Comet 55P/Tempel-Tuttle in view, the comet is currently, around the orbit of Jupiter. Moving forward to the year 2031 brings it into the inner solar system. This is the year that it should be coming to its perihelion again. Again, its perihelion is about the distance between the Earth and the Sun.

As the comet comes into the inner solar system, past Mars and near to the Earth and Venus’s orbits, it goes around in the opposite direction to them. This comet is orbiting the Sun in retrograde. It’s going against the direction of the inner planets. Even further out, although Jupiter is moving a little bit slow, it’s also moving opposite the direction of Jupiter. All of the planets in our solar system orbit the Sun prograde. This comet, and certain other smaller objects, do orbit the Sun in retrograde. The retrograde motion of Venus, Mercury and all of the planets is an apparent motion, it’s really illusory. Focusing on the comet’s perihelion, it very clearly moves the opposite direction to the Earth around the Sun. That means that when this comet leaves behind a trail of material, that trail of material is also moving retrograde. It crashes into the Earth essentially head on, both things are moving towards each other rather than the stream of material moving the same direction as the Earth and our gravity having to pull it into our atmosphere. The material is coming straight at us even without our gravity pulling it down, which of course it also does. This makes the Leonids very fast meteors, faster than any other shower.

So that is Comet Tempel-Tuttle. One of the most interesting things about it is the fact that it is retrograde, and then of course the fact that it creates the Leonid meteor shower. The comet just crosses the Earth’s orbit at perihelion. Its distance to the Sun gets just under one AU, but not much closer than that. This puts its perihelion right on our path. It leaves behind a lot of material and that material is also traveling roughly the same direction as the comet as the stream of material that the comet leaves behind.

That’s just a little bit on the Leonids, which of course have just happened back on the 17th of November. They’ll happen again next year and we will talk about them again then. I hope that you enjoyed this look at the comet which gives rise to the Leonid meteor shower and a little bit of extra information about it. If you did enjoy this piece, then please do like it. If you enjoy this topic, 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.