Caoimhín's Content

While comet 12P/Pons-Brooks was making its approach to the Sun, it became visible to the naked eye from the Northern Hemisphere, under good conditions at least. It was also quite close to Jupiter in the sky during the recent total solar eclipse visible from North America. This lead to the comet getting a lot of attention in the media. It did also, briefly, look like it had horns due to material being ejected from the comet as the Sun warmed it, leading to the nicknames of “Devil Comet” or “Devil’s Comet”. Now however, the comet has passed its perihelion, it has gotten as close to the Sun as it’s going to get. From here on out the comet is leaving the solar system, and it won’t come back around for nearly 70 years. At the moment, it’s still a little closer to the Sun than we are, and closer to the Sun than it is too us. 1 AU is the average distance between the Earth and the Sun, so using AU’s to measure things makes it very easy to tell if it’s closer to the Sun than we are or further from the Sun and how many times. If something is 0.5 AU from the Sun, it’s half the distance between us and the Sun, it’s twice as close, if it’s at 2 AU then it’s twice as far from the Sun as we are. Looking at the comet at 1.5 AU from us, it’s as far from us as we are from the Sun plus half that distance again. Comet 12P/Pons-Brooks is still close enough, to us and the Sun to technically be visible, but it’s pretty much impossible for us to see it here in Ireland.

If we take a look at the sky with no atmosphere, to make sure we can see the comet during the day, we’ll see that it is below the Sun in our sky. This means that it ends up setting in the evening before the Sun actually sets for us here in Ireland. On this part of its journey it is very much below the ecliptic, assuming South of the ecliptic is below, of course up and down don’t apply that much in space. With no atmosphere, the line of the ecliptic is quite easy to spot at the moment, thanks to all the planets and the Moon. The planets don’t perfectly align with the ecliptic, some of them are a little inclined, but not by much, If you were to draw a line of best fit through the planets we can see, trying to get as close as possible to all of the planets and the Moon while still going right through the Sun, that will approximate the ecliptic. The ecliptic does curve across our sky from East to West, but looking at the sky in Stellarium or other software, we can tilt our view making the line appear straight. We are looking at a bit of a flat projection of what would be a curved sky. With the ecliptic pretty much going left to right across the sky, we can see that the comets path is almost vertical, perpendicular to the ecliptic. If we were to take a look at the orbital path of this comet from outside the solar system, looking at the whole orbit, we would see a very big, very eccentric, ellipse, the orbital path of the comet is even further from a circle than the orbital paths of the planets. Not only is it highly eccentric, it is highly inclined, with the comets path taking it over and under the Sun, perpendicular to the paths that the planets take.

Comets often show highly inclined orbits, as do other objects from the edges of the solar system. While the planets and even the asteroid belt orbit around the equator of the Sun, a more spherical arrangement of objects seems to surround the outer solar system, the Oort cloud or Öpik–Oort cloud. As a solar system forms, and we have now seen evidence of fledging solar systems forming around other stars, the star usually begins by forming a disk of material around itself. This disc is similar to the ring we see around Saturn, but on a much grander scale. Material that is a bit further away from the star can still be bound to it by gravity, but less influenced by the stars rotation, allowing it to form a more round shell, with objects orbiting in various paths. Many comets originate from this far out, disturbed by passing stars or other massive objects, they hurtle in towards the Sun, but often maintain their highly inclined orbit.

Looking at the distance between comet 12P/Pons-Brooks, the Earth and the Sun over the span of a few days, we can see that at some point of its orbit it is moving away from the Sun and towards us, until it passes us and starts moving away from both the Earth and the Sun. By the 2nd of June it will be just about 1.546AU from the Earth, and that’s the closest it’s going to get to us, it happens to occur while the comet is on its way back out this time. By then it will be further from the Sun than we are. As the comet’s orbit is so long, and also because it moves a little slower on the further out portion of its orbit, as we orbit the Sun we will move closer to it and further from it, but on average its distance from us will increase until it reaches its furthest and stars returning towards us. AU’s are not the most common unit of measurement, and 1.546 AU seems like a small number, but it roughly 231 million km, so near is a relative term in this case.

As demonstrated in the video, the comet is not above the horizon during the night for us in the Northern Hemisphere any more. Luckily, for those in the Southern Hemisphere, it can still be above the horizon at certain times of the night. We will take a look first from the very bottom of South America, about as South as we can get on a large landmass without heading to Antarctica. Using software like Stellarium, we aren’t tied to dry land, and we could easily position our simulated view in the middle of the ocean. However, I like to give the best chance possibly that someone out there will actually get to use the information I provide. I may not have any viewers, readers or followers in the Southernmost parts of Chile and Argentina, but there is a higher chance that I have viewers who live there than on Antarctica. If any of you are in Tierra del Fuego, this is roughly how you could see the comet. At very low latitudes, the ecliptic will appear to follow a shallow angle above the horizon, much like it does here in Ireland. Of course, the comet does not follow the ecliptic, but viewing it in the morning in the far South still puts it pretty close to the horizon as well. The comet is a little further form the Sun than it was in April, so it is after getting a little fainter, around a magnitude of 7, which in Dark Skies is still just barely visible to the naked eye. Through binoculars in a sufficiently dark sky, you may still be able to see its tail, as it is still close enough to the Sun for one to be formed.

Looking at the comet in the morning, with the Sun’s glow revealing the Sun’s location, it is easy to see that the tail of the comet is pointing away from the Sun. By observing its position relative to the stars over the course of a few days, you can also tell that the comet itself is moving away from the Sun. The comet is moving in the direction its tail is pointing, which is definitely a little counterintuitive given that tails usually follow whatever has them. This helps to show that the tail is generated mostly by the solar wind, blowing bits off the comet, and generating this tail stretching out away from the Sun, regardless of the direction that the comet is moving. As the comet continues its outbound journey, the tail will fade and disappear, as the comet refreezes further from the heat of the Sun. In this simulation at least we can just about see the sort of double tail a comet can have. Different parts of the tail will be affected differently by different factors. Charged particles are more likely to be deflected by the Sun’s magnetic field, more massive particles are more likely to be influenced by the motion of the comet, leading to different particles moving in slightly different directions. For some comets, this can lead to two quite distinct tails pointing at almost right angles away from each other, but it does depend on the comets composition and distance from the Sun.

Moving closer to the equator will let us see most objects easier at sunset and sunrise, at least if they follow the ecliptic. This comet of course does not follow the ecliptic, but around the equator still gives us a better chance to see it than high northern latitudes. It remains quite low to the horizon as the Sun is setting, but it is still above the horizon at sunset, even though it is quite close to the glow of sunset. At roughly magnitude 7, dark skies are still required to spot it with the naked eye. It also helps to be familiar with the stars you normally see, as that will help this occasional visitor stand out from the repeating background of stars. While the comet is a little closer to the Sun, it’s brightness is a little bit higher, up to magnitude 4, which is usually quite visible to the naked eye even with some light pollution, though it is still easier in dark skies. It will also be in the sky for a shorter length of time while ti is closer to the Sun.

As I’ve been repeating, this comet has a period of over 70 years, about 71 years. Unless you are very young, you may not still be here in 71 years when it comes back. For those of us in the Northern Hemisphere, we have had our chance to see it. For anyone in the Southern Hemisphere, you still have sometime left to catch it, but it is very nearly our last chance to see before it leaves the sky for the rest of our lives. Comet 12P/Pons-Brooks at its very brightest, was still out of view for many people inn light polluted areas, and even ender good conditions could be tricky to spot with the naked eye. Other comets can be much brighter and easier to see, including one of the most famous, Halley’s Comet. Halley’s Comet has a similarly long period, over 70 years, but it will be back relatively soon, in 2061. Join me next time when we journey to that future date to see how that comet will look when it returns to us, maybe along with an other future event. If you want to make sure that you catch the video and article when they come out, you can subscribe to this website or to my YouTube, and hopefully I will see you back here then.