Caoimhín's Content

Today, we’re going to be taking a brief and general look at the comet 12P/Pons-Brooks. As with all comets, and most things in the sky, there is a pattern to the names, 12P for being the 12th periodic comet and Pons-Brooks for the surnames of the two astronomers recognized for its discovery. This comet has been in the news a bit recently, and has been visible through telescopes for a while, but just now it is starting to be a viable target for naked eye astronomy. Comets can be faint, and this one isn’t particularly bright, or even at its brightest, which will make this tricky, especially in areas with a lot of light pollution. These videos usually assume the city pollution of a smaller city, Cork City in Ireland to be exact, so larger cities will often suffer from more light pollution than what is show.

On the evening of the equinox, the 20th of this month, both Jupiter and Mercury should be visible as the Sun sets. Jupiter will be reasonably high in the sky, especially as the sky begins to darken, and Mercury is bright enough to shine through while it is still well above the horizon, though much lower than Jupiter. As the sky darkens, Mercury will sink towards the horizon, but if you can keep it in view it will be easier to spot thanks to the darker conditions. Keeping it in view is the tricky part, and a clear horizon such as a western coast will help. Mercury is a tricky target, but a clear view in this direction is helpful for spotting the comet as well. Luckily the comet is a little higher from the horizon, though not quite as high as Jupiter. It is also further to the right, or North, than either Jupiter or Mercury, but not by much. It makes a squat triangle with the two planets in the sky. Once Mercury is close to setting, the sky should be dark enough for the faint dot of the comet to appear.

As I admit in the video, this is pretty tricky to see with the naked eye, but with luck and good conditions it should be visible. Better conditions will of course help, clear skies, a good elevated viewing location and less light pollution would all make it a little easier. Taking a look at the same view from a location with darker skies shows that the comet is a bit easier to see, and as the sky darkens the Andromeda Galaxy will come into view above it and a little further to its north. Nearby is the Triangulum galaxy, and the wide field of view afforded by Stellarium allows us to see the two galaxies, the comet and the two planets at the same time as the Sun sets. This is under a level of magnification and would be tricky to see. This is where it will be on the equinox, as we move forward to the end of the month, the comet will move into line with Jupiter and Mercury, ending up quite close to Jupiter in the sky in early April. Of course, in early April Jupiter will also be a bit close to sunset, keeping the comet a challenging object to observe. The comet appears to cross the ecliptic as it does this, and the comet does orbit the Sun on a very different path to any planet. As we move towards summer time, the comet will appear under the ecliptic and almost in the direction of the Sun, which will make it difficult to see from most locations.

Taking a closer look at the comet on the night of the equinox, the tail of the comet becomes visible stretching behind it. This is how we would expect and how comets are generally show, with the tail stretching out behind them, pointing away from the direction that they are travelling. This is only true while the comet is heading towards the Sun. A comets tail isn’t caused by its motion in space, but by the Sun. The solar wind is the stream of particles moving out from the Sun and this is what blows gas and dust away from the comet. It is also the heat of the Sun that melts heats parts of the comet into vapor for the tail, they lose their tails when they are far enough from the Sun. Due to the way the tail is formed, it always points away from the Sun, without much regard for the direction of the comets motion. Right now as the comet moves in towards the Sun, the tail will stretch out behind it, as we’d expect. As the comet comes around the Sun and passes its perihelion, the tail will still point away from the Sun, the same direction the comet is headed. This will put the tail ahead of the comet, leading it as the comet moves out into space, where it will lose the tail as it cools.

In early April the narrow Crescent Moon will join Jupiter and the comet in the early evening sky, but quite close to the horizon and difficult to spot from here in Ireland. On the 8th of April, the night of the Full Moon, the comet will still be quite close to Jupiter. Comets can take a while to travel through space, but they are moving at their fastest when they are close to the Sun, as the comet will be in April, meaning they are only at their brightest for a reasonably short period of time. Just like planets, comets don’t make their own light, so we can only see them when they are reflecting light from the Sun in our direction. As the comet moves away from the Sun, roughly in our direction, it will fade and eventually become almost invisible.

This comet is considered a short period comet, falling in a class group known as Halley type, with periods between 20 and 200 years. Comet 12P/Pons-Brooks has a period of 71 years, which certainly seems long, but many comets can take far far longer, if they ever come back at all. For this reason, for many people this will be a once in a lifetime comet, you’ll need to be quite young this time to have a good chance of surviving until it comes back around in 2095. I’ll hopefully be turning 100 that year so fingers crossed. This year however presents a particularly magical chance. Thanks to the solar eclipse on April 8th, you might get to see the comet just next to Jupiter in the middle of the day, during the eclipse. Protective eyewear does need to be used to observe a solar eclipse, and precautions need to be taken with telescopes as well. If you have the right eyewear or gear, you can often see bright planets during solar eclipses, especially Venus. This year, there just happens to be a comet in the right position as well. Th April 8th eclipse is being called the Great American Eclipse, presumably because it will look good form North America, centering on the Northern United States the path of the eclipse travels up from Eastern Mexico into Western Canada. There will be a video dealing more with that eclipse and it will almost certainly mention the comet as well. As the comet starts leaving the solar system again, it will come a little closer to the Earth, about 232 million kilometers from us, which isn’t that close but is the closest we get to the comet this year. The comet didn’t get quite as close to us when it was on its way in towards the Sun, partly thanks to its highly inclined orbit which takes it above and below the ecliptic and the planets.

In the video, after looking at the countryside sky, we return to the city to use a telescope, using the simulated telescopes available in Stellarium. Even a quite small telescope or pair of binoculars will begin to show some fuzziness, helping to show that it is not a star. The rocky body or nucleus of the comet is surrounded by a fuzzy region of gasses called a coma. The trail stretches out behind the comet, but with a small telescope or binoculars this will be hard to spot as it is comparatively faint. Even medium sized telescopes will begin showing the tail, especially as the sky gets dark. In Ireland at least this will bring the comet below the horizon, though it was circumpolar for a while as it came in to the inner solar system and still be from certain locations.

Comets are a particularly interesting object to spot, as rare visitors into our part of the solar system, and at 71 years 12P/Pons-Brooks is certainly an infrequent visitor. This year, some people will have a chance to see the comet at the same time as a solar eclipse, so those of us at other locations can’t let them have all the fun. I’ll certainly revisit this comet during the upcoming eclipse video and possibly when it comes our way on its way out of the solar system. If you’d like to catch those articles then you can subscribe to this website, you can also subscribe to the Caoimhín’s Content YouTube channel for the videos. With some interesting events coming up, I hope you’ll come back to check them out.