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Today we are going to be looking at a meteor shower that is coming up in the month of December. Taking a look at the sky for mid-December, just coming up to 8 o’clock Gemini is already in the sky. We’re looking for the Geminids, the Geminid Meteor Shower and the radiant is up in the head of Gemini.

If we push a little bit later we can see that there are other meteor showers that are going on in December, but the Geminids are really the ones that we’re interested in. Having a look at a few of these other ones, for example the Coma Berenicids. These are the meteors from the hair of Bernice, and I’m not joking. Taking a look the constellations themselves, the radiant of the Coma Berenicids is pretty far from the constellation of Coma Berenice, which is a lock of hair just east of Leo. This is a good example of these meteor shower radiants being named after the constellation that they come from, but they can be a little bit off. The Coma Berenicids, radiating really from the tail of Leo, are peaking on the 16th of December Their maximum Zenith hourly rate is 3, so not a particularly big meteor shower. The December Leonis Minorids, in Leo Minor, are also a pretty small shower, they’re peaking on the 20th of December with a Zenith hourly max of 5, which of course isn’t much either. The Alpha Hydrids, in Hydra, are peaking on the 9th of December, so a little bit earlier than the date we’re looking at, with a max rate of 7, which isn’t terrible. However, looking back on meteor showers like the Leonids and the Perseids with rates of 20-ish, these meteor showers are pretty small. Also there are the December Monocerotids in Monoceros, the Unicorn, peaking on the 9th of December, with a zenith hourly rate of 3, so also not particularly good.

The Antihelion point is there as always. It drifts across the sky as it’s always directly opposite the Sun. It’s directly behind the Earth compared to the Sun, so it’s going to change where it is in the sky, roughly passing through the zodiacal constellations. At around 8 in mid-December we’ve got Aries, Taurus, Gemini, Cancer, Leo and Virgo all in a row. If we move through time, we’ll see the antihelion moving through those constellations, the exact opposite position to where we would be seeing the Sun during the day. Indeed, all of the radiants drift around because the Earth is moving through the streams of material that the meteors come from. On different nights we’ve turned a little bit more and that’s caused them to hit the atmosphere in a slightly different place.

The Geminids are peaking on the 14th of December. We’ll move around and try to find the exact peak as well, but more importantly the zenith hourly rate has a max of 120. The Geminids are generally regarded as the best meteor shower. I am a fan personally of the Perseids, but the Geminids are the one that is widely recorded as the best. Starting just after midnight and pushing up to the morning of the 14th, that’s we’re getting up to the max for us in Ireland. We hit the max of 120, the absolute peak of the shower, at just, just 7:30 in the morning. For us, watching this meteor shower from a little bit after sunset on the 13th through to the morning of the 14th seems to be best. At first the radiant is pretty low in the sky, it’s coming up just a little after 7 o’clock. The sky will at least be fully dark at this time. This early it’s at a rate of 74, but as we get later in the night, the rate climbs and the radiant gets higher in the sky. The closer to the zenith the radiant is the better, and as the Geminids are right above the south, the highest point that they’re going to reach, the zenith hourly rate is 99 and we’re getting 39 for the local hourly rate. That is of course limited by light pollution as well. As with all meteor showers, it’s better to head out to the countryside, that’s where you’ll get the optimum view.

Once we’ve pushed out to the countryside, the local hourly rate is 94 and the zenith hourly rate, what the rate would be if the radiant was actually at the zenith is 99, so we’re pretty close. The max of 120 comes up later in the morning, but even though the rate continues to increase, for example as we get later the zenith rate goes up to 118, but it’s getting lower in the sky so that’s going to cause us to miss a few meteors. They’re going to be visible to people below our horizon, but for us it brings down the local rate to 71. Then of course the Sun starts coming up and that’s going to make the meteors much, much harder to see. The Geminids are considered one of the best meteor showers, it has these zenith hourly rates of 120 pretty much every year and it is regular in that way. It doesn’t seem to produce meteor storms like the Leonids do where there’s hundreds of thousands of meteors, but those only happen every few decades. The Geminids are regularly very productive, and they peak in December, very close to the shortest day of the year, so we have a nice long dark night to observe the Geminids and hopefully, here in Ireland at least. This far into the Northern hemisphere, it is winter, so there’s a good chance that it will be a cold, clear night. If there is a frost, then there’s a good chance there will be hardly any clouds in the sky, there won’t be much available humidity because everything will be frozen, and that makes it much easier to see meteors as well. A very clear night sky with lower humidity tends to happen when it’s very cold here in Ireland, otherwise the humidity can be quite high.

The parent body of the Geminids is a minor planet, 3200 Phaethon. This meteor shower is caused by what could be considered an asteroid, it doesn’t really seem to be a comet or it at least doesn’t behave like a comet. It doesn’t produce a tail when it goes around the Sun. It does have a similar orbit to a comet, but it also seems to be a ball of rock. Little bits of rock falling off this object are what create the Geminid meteor shower. This asteroid-comet object is a little bit hard to define, so it often gets called a rock comet, and it does have a pretty metal name, Phaethon, which is appropriate for a rock comet.

Currently the asteroid is way out in space, at just magnitude 18. It was discovered in 1983, so this is a reasonably recent discovery. It was only in the 80s that we found this comet was or this rocky object, and then that this object was the parent body of the Geminids. This was something that was only figured out comparatively recently. It’s particularly big, just six kilometers across, much smaller than some other comets. We will need to move through a fair bit of time to get it back to its perihelion because it does have a longer orbit. It is a quite similar orbit to the orbit that a comet would have so we would have to move through quite a lot of time to bring it back in to the inner solar system.

What we’ll do is we’ll head out to the solar system observer to see if we can bring it around to its perihelion whenever that is and see exactly how comet like this orbit is. The asteroid Phaeton is currently past the orbit of Mars, but still inside the orbit of Jupiter. Moving through time days at a time, the asteroid is going to move pretty slowly. These things do take a while to move around, so we’ll move through time by years instead. Going back just a couple of years brings it back to its perihelion. It’s inside Earth’s orbit, just crossing Venus’s orbit in December 2023. Moving back to November, it gets inside Mercury’s orbit. Now we should start moving by days because the motion of the comet is so much quicker when it’s at perihelion compared to when it’s at aphelion, when it’s further out from the Sun. It looks like it last had its perihelion sometime around the 19th of the 10th 202. It’s definitely quite close to the Sun, a distance of just 0.164 AU, very close. Of course, we’ve been moving back in time from 2025 to then, so we can keep going to see the comet come into the inner solar system.

As it came in towards the solar system it crossed the Earth’s orbit around the 13th of the 9th We had to jump through a couple of years to get the comet from almost out by Jupiter’s orbit back into the inner solar system and we only have to go through a few weeks to see this asteroid come all the way around the Sun, from crossing Earth’s orbit on one side to crossing Earth’s orbit on the other. It looks like it’s crossing Earth’s orbit pretty close to late December around the 29th on its way out, even though the meteor shower caused by this asteroid is peaking on the 13th and 14th. The orbital parameters of this object are actually very up to date, the orbital elements are for 2025 and we are looking back years here, so that is going to make a difference.

Zooming back out a little bit we’ll bring it to aphelion. We’ll come back up to 2025, and it looks like it’s close to aphelion now. Just earlier this year by the looks of it, the object was out at 2.37 AU. That number keeps getting bigger as we move from November into December. It looks like it’s actually coming up to its aphelion just about in December, just about the time that the meteor shower that it generates is peaking. We get up to 2.403 AU from the Sun just around the peak of the Geminids, so that’s interesting. This comet-like object took from 2023 till 2025 to get out here. It will presumably take about another year for it to get back in, so it seems to have a period of about 2 years. Really it’s a little bit shorter, about 1.45 years ar so.

This strange object, this rock-like-comet, is the parent body to the Geminid meteor shower, and it loops around in a pretty short but also quite comet like orbit. Its orbit is much shorter than the orbits we might be used to for true comets, because this doesn’t actually seem to be a comet, it is just some object that gives rise to the Geminid meteor shower. That is asteroid 3200 Phaethon. It seemed like an appropriate object to cover, an interesting object to cover, given that the Geminid meteor shower is coming up this month and I will mention it again when we get a little bit later into December.

I hope you found that interesting. I hope that you enjoyed this piece, if you did, please do like it and 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.