Comet 12P/Pons-Brooks has finally arrived in our skies. It will make its closest approach to the Sun, perihelion, tomorrow at a distance of around 117 million kilometers from the Sun, and at its brightest.
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Comets are frozen bits of rock - sometimes called dirty snowballs. They are not very big - this comet is 34 kilometres wide. They have a solid, rocky body called the nucleus.
As the comet gets closer to the Sun, the ice turns to gas, called sublimation. Instead of melting, it goes straight to a gas. As it does, the frozen carbon that turns into a gas gives it the green colour. This gas is gradually blown off by the Sun, and gives the comet its tail and glow.
However, this comet is prone to outbursts. The Sun heats up the comet, and the pressure of the gas is released quickly, leading to very big outbursts.
![A comet moving through the sky. Picture Shutterstock A comet moving through the sky. Picture Shutterstock](/images/transform/v1/crop/frm/203652251/1b9dc48b-1bd7-4e73-a460-2c9fb5e22ef4.jpg/r166_0_4234_2286_w1200_h678_fmax.jpg)
The tail is always in the opposite direction of the Sun, as it is the Sun's wind blowing it. The outbursts though can occur at different times and directions, giving different shapes. Some have compared them to horns, leading it to be called the horned comet or devil comet..
The real name is Comet 12P/Pons-Brooks. P is for periodic comets, those that regularly orbit the Sun, and cataloged in order. 1P is Halley's comet. Pons-Brooks are the two credited discovers of the comet, and comets have to be named after the individual or group who discovered them.
The comet is visible in the western sky. As the Sun sets, about 20 - 30 minutes after sunset, look towards the west. It will just be visible to the naked eye, but tough to spot. To best enjoy, it, grabs some binoculars. You are not looking for a bright star, but a fuzzy green object. However, we also have the bright Moon making it difficult.
However, from ANZAC Day, the Moon will rise after the comet is visible so waiting until then and next weekend will make your comet hunting easier.
It won't be a big spectacular site, but still worth checking out. If you want a potentially brighter comet, wait until end of September / October comet C/2023 A3 (Tsuchinshan-ATLAS).
C is for it being a comet with a really long orbit that doesn't come back often (if ever). Discovered in 2023, and A is the half-month code (1st half of January), and it was the 3rd comet discovered then - hence C/2023 A3.
It has an orbit that has taken millions of years to come into the inner Solar System, and will be less than 59 million kilometres from the Sun on the 25th of September.
Since it is making its likely first trip, and getting close to the Sun, it could become very bright, brighter than most stars. It will have lots of ice to turn into that gas that glows, and by getting even closer, could put on a show.
Since it is not a stable, periodic comet like 12P, it could actually get too close and disintegrated, and disappoint us.
Comets are very hard to predict, making them a lot like cats. They have tails, we like to look at them, but we never know what they will do next (and not even sure if they like us).
But both are still worth taking a look at.
- Brad Tucker is an Astrophysics and Cosmologist at Mt Stromlo Observatory and the National Centre for the Public Awareness of Science at the ANU.