EXPERT REACTION: The Devil Comet is now visible in the sky as it passes Earth

Comet 12P/Pons-Brooks is back, after seven decades in the icy depths of the Solar system. It's currently visible with the naked eye, low in the sky to the west after sunset - but it is far from spectacular. More like a fuzzy blob than a great comet! It will gradually get higher in the evening sky over the next few weeks, as it very slowly fades - so the best time to look for it might actually be in the first two weeks of May, when it will be sandwiched between Orion and the western horizon. Search for it with binoculars, after the Sun has set, and once you've found it, then see if you can spot it with the naked eye. But this comet will probably be best seen as a photography target - a good long exposure with a camera will show it up much more clearly than how it will appear to the naked eye! But there might be something even better in store - another comet, C/2023 A3 (Tsuchinshan-ATLAS) is currently swinging sunward, and may turn out to be really spectacular in October. So perhaps consider 12P/Pons-Brooks to the be a good warm up before a potentially spectacular main event later this year!

Any celestial event, whether it is a comet passing through the night sky or a transient meteor shower or perhaps an eclipse, is a great chance to look up at the sky and remind ourselves about our place in the Universe. It’s not yet clear exactly how bright or visible Comet 12P/Pons-Brooks will become, but it’s definitely worth taking the opportunity to try spotting it - it won’t be back for another 71 years! Those hoping to catch a glimpse should look (or point binoculars) in the direction of the western horizon just after sunset throughout the rest of April, and search for a fuzzy blob near Jupiter. Hopefully it’ll put on a bit of a show for us! It's also worth keeping an eye on Comet C/2023 A3 (Tsuchinshan-ATLAS), which will pass by around September 2024 and may end up quite bright in southern skies.

Comets are amongst the most fascinating and at times spectacular astronomical objects. Fleeting visitors to the inner solar system with tails of gas and dust stretching millions of kilometres across space. Comet Hyakutake stretching across the night sky is vivid in my mind despite it being decades ago. There have been some beautiful images of Comet 12P/Pons-Brooks recently, but they were taken with sensitive cameras and telescopes. Unfortunately, Comet 12P/Pons-Brooks will appear faint and fuzzy to the unaided eye, although better views will be possible with binoculars and small telescopes. I will try taking a look at this comet from my home in Melbourne on clear nights, but the best views will be in the country away from light pollution. Definitely take a look at Comet 12P/Pons-Brooks if you get the chance, but remember that bigger and brighter comets will, at some point, grace our skies.

Comet 12P/Pons-Brooks has swung past Earth many times before. Knowing that it has a period of 71 years in its orbit around the Sun, it's possible to match it up with appearances recorded by ancient observers. The comet was recorded by astronomers in China possibly as early as 245 CE (AD). In 1385, it was described in the annals of the Ming emperors, where comets were called ‘guest stars’. In the ancient world, celestial events were interpreted as reflections of events on Earth, sometimes heralding doom, and sometimes positive change. Now we’re more concerned about whether a light streaking through the sky is a piece of space junk about to fall on our heads, or an asteroid on a collision path with Earth. By comparison, comets are friendly visitors; and this month Australians have a unique opportunity to follow 12P/Pons-Brooks before it leaves us for another 71 years.

This brilliant green comet with a sinister crescent nucleus will continue to brighten over the next few nights with a peak around April 22nd. Look towards the western horizon near sunset for a nice pairing with Jupiter. I recommend binoculars to spot the comet given it appears at dusk.

This comet has a fascinating history of being 'discovered' and 'rediscovered'. In 1812, the French astronomer Jean-Louis Pons first observed this interesting comet. In 1884, the British-American astronomer William Robert Brooks reported seeing it again. Perhaps it was difficult to determine the orbit and predict when it would return, which is why another observation was required to confirm that it was the same comet. It took generations of astronomers to come and go before the comet could be officially named after both astronomers, acknowledging two observations made over 70 years apart. 

Comets are messengers of the deep space. They sleep most of the time, hibernating. They wake up to their full glory only when approaching the Sun.

The 'Devil’s Comet' name comes from its appearance at times earlier during this apparition, when there were short-term increases in the comet’s brightness, accompanied by an asymmetry in the coma (the diffuse area surrounding the nucleus).

There were two thin, brighter regions with an apparent gap between them, looking somewhat like two horns trailing the nucleus (depending on one’s visual interpretation). These may have been due to temporary enhancements in ejection of material from the nucleus in one or more isolated locations.

These appearances were only temporary. (Evidently, a similar phenomenon was seen during its 1884 apparition.) See examples here and here. 

'12P' indicates it was the 12th comet found to be periodic, i.e. returning with a known orbital period. Discovered by Jean-Louis Pons (French) in 1812, and accidentally recovered by William Brooks (American) in 1883, hence the compound name.

Orbital period is 71 years. Its orbit does not intersect that of the Earth.

Perihelion (closest to sun) will be on April 21st 2024. Its closest approach to Earth will be on June 2nd, at a distance of 232 million kilometres. 

It currently has reached naked-eye brightness. Nearing perihelion, it may brighten further, though comets are notoriously fickle with regards to future brightness estimates. Sometimes they are fainter than expected, sometimes brighter. So an expectation in this regard is not a guarantee.

The duration of this period of naked-eye brightness is quite short, perhaps until mid-May. Peak brightness is expected around April 23rd.

City lights, moonlight, twilight, or a low position in the sky can make seeing something that should be visible to the naked eye (judged only by its observed magnitude) difficult. The darker the sky background, the better. Binoculars may help.

Currently (18/4), low in the north-west after sunset, setting at around 19:15. A clear horizon to the north-west is needed.

It climbs higher in the sky over the coming days, but will still be quite low to the north-west. 

Currently to the west of Taurus (west of the Hyades and Pleiades star clusters), then heads closer to the bright blue star Rigel in Orion over the coming month, so also moving further south in the sky as seen from Adelaide.