Comet Wirtanen is coming back – again

Comet 46P/Wirtanen is returning in December 2018, and it’s going to pass close to the Earth. It’ll look good in binoculars from the Southern Hemisphere.

Wirtanen is a dirty snowball. It’s mainly a lump of ice with dirt and dust as well as other chemicals through it. Like the planets, they stay in orbits around the sun. But unlike the planets, which are in nearly round orbits, comet orbits are stretched-out oval shapes, with the comet coming in close to the sun, but most of the time being very far away.

When they’re far from the sun they just stay as they are because it’s cold, but when they get close to the sun things start to happen.

Wirtanen never goes very far from the sun, which means it comes back more often, every 5.5 years. This is way more often than Halley’s Comet, which comes back every 75 or 76 years. (Incidentally, my grandfather saw Halley’s Comet twice.)

Comets are hard to predict

If, like me, you’re old enough to remember the Halley’s Comet fly-by in 1986, you’ll remember that it got wildly hyped in the media, to the point where people were expecting a huge spectacular show. You’ll also remember that we were disappointed when the comet turned out to be a fuzzy blob with only a short tail. This is my own photo from 1986 (shot on film with all sorts of scratches).

Halley's Comet, 1986

We really don’t know how bright Wirtanen is going to be, but we do know where it’s going to be. Wirtanen is going to approach very close to the Earth (but still at a safe distance), starting in the south, and then retreat towards the north. It will be closest to Earth on the 16th of December 2018. From Australia, the comet is going to drift (very photogenically) between the Pleiades and the bright star Aldebaran. It will have approached from above in the couple of weeks prior to its closest approach, and in the period after the 16th, it will go below the horizon as Australian viewers see it.

Sky and Telescope magazine have produced a sky map that shows the path of the comet in mid-December. I’ve rotated the map so it’s the right way up for Australian viewers. The line from the top to the bottom shows the path of the comet, and dates in December are marked along the line.

Extracted from https://www.skyandtelescope.com/observing/bright-comet-prospects-for-2018/ (Copyright 2018, Sky & Telescope Media).

How to see it best

The thing about comets is they can get long tails. If you have too much magnification, you’ll get too close and not see it all. Also, the tail can be quite faint, and so the more light-gathering ability, the better. Because of this, probably the best thing to be using for comet-spotting is a pair of binoculars.

Binoculars come in different sizes, which are rated by numbers like 10×42. The first number is the magnification, and the second number is the width of the main lens. For comets, you want a log magnification and a large lens size.

Optics Central has quite a number of binoculars that fit this bill:
Bushnell Trophy Xtreme 8×56 gives the maximum light gathering ability at this magnification
• The Bushnell Trophy 8×42 is a slightly smaller and lighter binocular
• The Steiner Skyhawk 3.0 8×42 is designed for birdwatching but is excellent for comets
• The Vortex Diamondback 8×42 offer a unique unlimited lifetime warrantee
• If quality is what you’re after, the Carl Zeiss Terra ED 8×42 has great image quality without the ultra-premium price bracket.

Bottom line

Comet Wirtanen is coming and will be best seen in the first two weeks in December 2018. We don’t really know how bright it will be, but it’s likely to be visible without any aid on a dark night. If you want to get closer, binoculars are probably best, with good light gathering and low magnification. Optics Central has a range of binoculars that will give you the balance you need to see the comet at its best.

Bill is Optics Central’s expert on astrophotography, telescopes and bird watching. You’ll find him in the Mitcham store on Fridays and Saturdays. Come in for advice on how to get the best out of your current telescope, what your next telescope should be, how to take photos of the sky, or even how to see some rare birds.

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2 Comments


  1. Alex Cherney has taken a brilliant photo of the comet – good enough to have been given an APOD (Astronomy Picture of the Day) by NASA.

    I asked him about the comet’s growing visibility. Alex reports that it’s now (end of November) visible unaided (so you don’t need a telescope or binoculars) from a dark sky site, as long as you know where it is.

    Alex is a member of the Astronomical Society of Victoria and gives annual talks on astrophotography.

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  2. My memory of Halley’s Comet is that the tail was more distinct than in your photo. I saw it from Royal Park, right next to the freeway with all its lights.

    My grandma said she’d seen it the previous time (1910), and that it was much brighter, but I imagine the night sky was a lot darker in 1910 Bethanga.

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