Comet alert! Here’s how to spot the best comet of the year

5th Dec 2018
Author: Tamela Maciel

Watch the skies this month!
A comet called 46P/Wirtanen makes a very close approach to Earth and will be bright enough to see with the naked eye. Here's all you need to know.

Comet 46P/Wirtanen's close approach

Comet 46P/Wirtanen is a relatively ordinary, fairly small comet, first discovered in 1948.

Its orbit only extends as far as Jupiter, which means it visits the inner Solar System very regularly – every 5.4 years these days! This comet is on the small size – just 1.2 kilometres across – in part because regular visits to the Sun mean that its volatile gases and dust have already been vaporised away in the heat.

But in December 2018, this ordinary comet becomes extraordinary.

This month, the Earth and 46P/Wirtanen line up such that the comet is at its closest approach to the Sun on almost the same day as its closest approach to Earth. This means that when the comet is at its closest (and brightest) to Earth, it’s also being vaporised by the Sun, shedding reflective dust and vapour that could make it even brighter.

The closest approach to Earth will occur on 16 December 2018 at 13:06 GMT. At this moment, it will be a mere 11.5 million kilometres away. While this comfortably large distance means we don’t have to worry about any collisions, it does make 46P/Wirtanen the 10th closest comet to fly by Earth since 1950 and one of the few predicted to be visible with the naked eye.

At this point, we should say that 46P/Wirtanen probably won’t be one of the ‘great’ comets like Hale Bopp in 1997. Because of its small size, it won’t have a spectacularly bright tail that accompanies bigger comets. Instead it will appear as a fuzzy point of light that moves across our winter night sky throughout the month of December. Nevertheless, if you’re under a clear night sky away from city lights, you should be able to spot 46P/Wirtanen throughout December if you know where to look (see below)!

The video from Comet Watch below shows just how the Earth and 46P/Wirtanen will make a close encounter.

How to watch

In mid-December, comet 46P/Wirtanen will become visible to the naked eye, making it the best and brightest comet of 2018.

In order to spot it, you will need a cloudless night sky as far away from city lights as you can get. So grab a friend and head for the hills!

You’ll also need a star chart for the month of December or a stargazing app so that you can find the main star constellations. Finally, print off the path of 46P/Wirtanen (see image on the left), so that you know where it should be throughout the month of December.

On or around 16 December 2018, head outside, look up, and let your eyes adjust to the dark. Look south and find the constellation Taurus. In particular find the bright ‘V’ shape of stars that makes the face of the bull.

In mid-December, 46P/Wirtanen will be passing above and to the right of this ‘V’ – look for a faint, fuzzy point of light about as bright as a faint star. On 16 December, 46P will be directly between the two star clusters Hyades and Pleiades.

If you have binoculars or a telescope, bring it out and 46P will look even better!

There are two caveats that could make spotting 46P tricky:

Clouds. If you’re a regular stargazer in the UK, you’ll know that clouds are a constant threat that can spoil even the best-laid astronomy plans. But 46P should be visible to the naked eye for several nights in mid-December so if it’s cloudy on the 16 December, head out on the next clear night.

The Moon. Unfortunately the Moon will be in the early night sky in mid-December, growing in brightest from first quarter to full moon on the 22 December. The Moon’s brightness will make it harder to spot the faint comet, so it’s best to wait until the Moon sets and the skies are darker. In mid-December, the Moon will set after midnight.

So in short, your best chance of seeing comet 46P/Wirtanen will be to head out after midnight on the 16 December, and find a spot far away from city lights. Look south and just above the constellation Taurus you should spy a fuzzy point of light that’s a comet! If it’s cloudy on the 16th, head out on the next available clear night.