Comet 46P – the hype builds…

You might have heard that there’s going to be a comet in the sky later in the year, and that it’s going to be a good one. Words like “stunning”, “dazzling” and “brilliant” are being used in breathless blog posts, FB posts and Tweets to describe the expected appearance of Comet 46P Wirtanen when it graces our skies in December…



Of course, the truth is rather different – but it seems that someone somewhere has passed a law that means every story about something visible in the night sky now, such as a meteor shower, an eclipse, a conjunction of planets or the close approach of an asteroid HAS to be hyped-up and sensationalised with over-the-top language, screaming UPPER CASE HEADLINES and ridiculously inaccurate graphics and artwork, which is a shame because a) experienced skywatchers know that astronomical events are gorgeous and fascinating enough without any hype and b) these giddy stories give non-astronomers totally unrealistic expectations and they end up disappointed by the real thing.

In the case of this comet, 46P, the truth is it MIGHT be visible to the naked eye in December, but it might not, and even if it is it will probably look NOTHING like the comets shown in the photographs and artwork being used to illustrate these hyped-up stories.

Comet 46P is a small (just over a kilometre across), short period (it orbits the Sun every 5.4 years) comet and was the original target comet for the ESA “Rosetta” comet probe, but that didn’t quite work out so the probe went to a different comet instead. There is a lot of interest in 46P because it is going to come very close to Earth this time. At its closest to us, on December 16th, it will pass us at a distance of “just” 7,220,000 km, which is close in astronomical terms but is actually almost nineteen times further away than the Moon. So we’re not going to see a Deep Impact-like comet streaking across the sky, trailing smoke and fire!

Screenshot_20181021-180320 b

A lot of the hype surrounding this comet comes from the calculations which have been made about its potential peak brightness, or “magnitude”. Comet experts have calculated that 46P might reach “magnitude 3” at its best, which suggests at first glance that it should be easy naked eye object, because stars of third magnitude are. However, it’s not quite that simple. Because the comet is going to be so close to us it will appear large in the sky, and its light will be spread out over a wide area, rather than concentrated in a point. So instead of looking like a long vapour trail in the sky with a bright head – the classic image of a comet being used to illustrate lots of the hyped-up 46P stories – the comet will appear like a greatly defocussed 3rd magnitude star, essentially a fuzzy, misty patch in the sky, brighter than many comets get but still faint enough that it probably won’t be visible from towns and cities without help from binoculars or a telescope.

collage 1c

It will look a lot better from somewhere with a dark sky, away from light pollution, but even there it certainly will not be “dazzling” or “spectacular”. Which is a shame, because we’re LONG overdue a really bright naked eye comet. One will appear, eventually, but sadly 46P is not it.

Does this matter? Really? Yes, it does, because people are fascinated by the night sky and enjoy seeing things going on “up there”, so to raise their expectations about things like this is wrong and leads to a lot of disapointment. It also results in the public wrongly blaming astronomers for their disappointment when really it was the fault of media hype and lazy journalism. Today far too many reporters are happy to lazily copy and paste info from a website, blog post or Tweet instead of taking two minutes to fact check the story themselves by emailing an actual astronomer asking for info.

So, bottom line: yes, there is going to be a comet in the sky at the end of the year, and astronomers are hoping it will be bright enough to see with the naked eye, but comets are so unpredictable that it might yet let us down (as so many have done in the past… grrr..!!!.) and only be visible through binoculars or even a telescope, if you know where to look for it. Ok, it will NOT be “dazzling” or “spectacular”, but it will definitely still be worth looking for, and you absolutely should NOT be thinking “Oh, I won’t bother looking for it now!” after reading this! If it behaves itself, 46P should at least be a very attractive sight in binoculars or a telescope, and if it fulfills its potential and reaches 3rd magnitude then it will definitely be worth you taking a trip out into the countryside to look for it glowing softly in the December sky. Comets this bright don’t come along very often, so you should definitely try to see it.

Don’t worry if you’re not sure what to do or where to look; lots of astronomical societies are already planning comet observing events in December for people who want to see 46P. A quick Google search will tell you if there’s an astronomy society on your area, then you can drop them a line to ask if they’re planning any events you could go along to. I’m sure they’d love to hear from you.

If you want to know where the comet will be in the sky in December I have some finder charts on another blog of mine, here…

Oh, and by the way, as December nears there are going to be lots of YouTube nutters, Anonymous mask-wearing fruit loops and ranting doomsday prophet “Pastors” making predictions about this comet destroying the Earth, etc etc…


Utter, utter, utter rubbish. They make the same ridiculous claims and predictions every time a comet is going to be visible in the sky. Ignore them. 🙂


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