Caoimhín's Content

As mentioned in the last video, there isn’t a lot happening in the sky this month. We do of course have the Micromoon, which I will get back to, but other than that, no eclipses or oppositions or meteor showers. However, despite not having any particular showers, we will still have some meteors. We usually have a few meteors in the sky, about 10 passing the zenith every hour, a zenith hourly rate or ZHR of 10. This is besides the extra ones we see during specific showers on certain dates of the year.

Technically, there is a meteor shower occurring at the beginning of February, the December Leonis Minorids. It is called this because it starts running in December, peaking on the night of the 19th, and even then only reaches a maximum zenith hourly rate of about 5. We’ll see far fewer, if any, as the shower finishes around the 4th of February. Leo Minor is the constellation, itself pretty small and faint. Luckily, even when this shower stops, there will still be a few meteors coming into the sky.

One radiant of meteors that we will see all year long is the Antihelion. In the video, we can see that this point stays with us from month to month. It remains in the night sky all night long, unlike anything else in the southern sky. Unfortunately, we don’t actually get to see it. Like the radiant of any meteor shower, it is the point that certain meteors will trace back to, even if their trails don’t actually reach it. Moving across the sky is also a trait we see with other radiants of meteor showers. Radiants usually mark roughly the direction of the trail of dust and gas that we move into and through as the meteor shower occurs. As they mark roughly where a trail of debris is, they don’t fallow the paths of the stars, causing them to appear to drift. However the Antihelion point is a little different. Depending on your frame of reference, it may not move at all.

A hint as to why this is is visible on the 24th of February this year. The Moon is very very close to that Antihelion point at around the time that it’s full, and this stays true from month to month. We know that the Moon is full when it’s on the opposite side of the Earth to the Sun and that’s what Antihelion means here. It doesn’t mean it’s going against the Sun, like and antihistamine that combats histamines, and it’s not Antehelion with an “e”, it’s not moving into the Sun or the beginning of the Sun, like an antechamber. Antihelion here really just means opposite the Sun and it does mean geometrically opposite, it is on the opposite side of the Earth to the Sun, always. This means that as we move around the Sun, although what stars are directly behind us will change, the Antihelion point will remain. This makes the Antihelion point appear to drift across the sky, really it is the stars’ positions that are changing.

From the Antihelion, we seem to be getting about four meteors an hour, a ZHR of four. There are other points in the sky where meteors regularly radiate from all year long. On the opposite side of the Antihelion we have the Helion point, between us and the Sun. Then we have another point ahead of us in our orbit, the Apex, and behind us in our orbit, the Antapex. These are places where meteors just happen, providing a background rate of meteors all year long. The Sun of course pulls dust and rock towards it self, but some of these bits crash into us instead, forming Antihelion meteors as they burn up in our sky. Some pieces of dust and rock are closer to the Sun than us, but as we come around our gravity can catch them, again pulling them into our atmosphere, forming Helion meteors. As the Earth moves along in it’s orbit, some debris that is in our orbit with us can be pulled down as well, leading to the Apex point in our direction of travel, while some meteors are pulled in even as we move away from them, leading to the Antapex point. There are two more regions, the Southern Toroidal Source and the Northern Toroidal Source. These are believed to pull in material left behind by comets passing over and under the Sun on highly inclined orbits, but they are less well understood.

There is a lot of debris in space, loose material created by collisions in the asteroid belt, left behind by comets and asteroids, and left over from the formation of the solar system. However, we still generally talk about space as being empty and compared to the atmosphere of the Earth it is. We are surrounded by atoms of gas, even if there is nothing else in the air around us. A cloud of dust in space is dust in a vacuum, with no molecules of gas in between, very different from a dust cloud here on Earth, where the dust hangs in our atmosphere of gas. Even in regions with some material, the vacuum of space is still emptier than a clear sky on the Earth, simply because of the layer of gas trapped by our gravity. The added friction created by an atmosphere and gas available to ionize is why we can see the meteors as they enter the atmosphere, there’s none of that to light up in space.

Now we’ll move onto the Moon. As mentioned, the Full Moon in February is a Micromoon, close to 400,000 kilometers from the Earth. If we follow the Moon into the New Moon in early March, we’ll see that the Moon gets closer to us, about 350,000km away. Every month, the Moon has an apogee and a perigee, sometimes it is the First Quarter Moon that is the closest and the Last Quarter Moon that is the fullest, but we don’t normally talk about Super Half Moons or Micro Half Moons. We’re really only interested in how close it is when it is full, unless we’re having an eclipse. An eclipse when we have a Micro New Moon will be an annular eclipse, something I will deal with in a video focused on eclipses.

If we follow the Moon through several months, we’ll see that the distance at it’s fullest changes slowly. The apogee and perigee of the Moon don’t sync up with the months, causing it to drift slowly over the course of the year. Once the Moon reaches its furthest point when it’s full, every full Moon after that will be a little less than its furthest point at it’s fullest. Once you see a Micromoon, we’ll have to start moving towards a Supermoon. Because the cycle from apogee to perigee doesn’t line up with the phases of the Moon, there’s no guarantee that the closest or furthest will exactly line up with the fullest, the same way that we aren’t guaranteed to see the Moon at it’s absolute fullest from any given location on the Earth. For this reason, a Supermoon and a Micromoon are usually considered to occur as long as a the moon is within 90% of its nearest or farthest when it’s full, sometimes it is stated as closer or equal to 360,000km away. This means that two Moons in a row could classify as super, each either side of true perigee. This all leads to a degree of variation in how super a Supermoon actually ends up being.

We often have a few Moons a year that count as Supermoons and the same with Micromoons, However, they are usually months apart, making it hard to compare them directly. Images such as photographs, if you make sure that you’re zoomed in the same amount that everything is the right scale, are the best way to actually see the difference between them. The difference in size isn’t quite as great as the difference in brightness, a Supermoon is brighter than a Micromoon by close to 60%, a much greater margin than the difference in size between a Supermoon and a Micromoon, which is about 14%.

Although there is enough variation to mean that some Supermoons are closer than others, and you can see a more super Supermoon after seeing another Supermoon earlier in the year, over long time periods the Supermoons are getting less super, and the Micromoons more micro. The Moon’s orbit like many orbits in space is changing. Mars has two moons, Phobos and Deimos, and Phobos will eventually crash into the planet, its orbit is decaying, causing it to spiral inwards, eventually it will fall into the planet. Deimos on the other hand is slowly spiralling away from the planet, as is our Moon. In the very distant past, tides were stronger due to the proximity of the Moon. Although the Moon is much smaller than the Sun, it is much closer to us, giving it more of an effect on us. As it spirals away, it’s influence will eventually fade. However, on average, the Micromoons will get more and more micro, so at least we have that to look forward to.

That’s all for this week, besides a big thank you to everyone who came out to the live show! That’s right, I do also perform live shows, most recently in The Friary here in Cork City, and you can book them here on this website! If you would like to come to a live show, make sure to check out Caoimhí’s Content on Instagram @caoimhinscontent which is of course my name everywhere. I hope you enjoyed reading this write up and I hope you will come back for the next one.