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Mon, 20 Mar 2017

A comet crosses the Plough

Comet 41P

Comet 41P photographed with a 300 mm lens  on 20 March.

Photo: Stuart Atkinson

A periodic comet is about to move fairly close to the Earth, and will be visible for those with good skies in one of the most easily recognised parts of the sky – The Plough (or Big Dipper for American readers). But Comet 41P/Tuttle-Giacobini-Kresak (let’s call it 41P from now on) isn’t one of those eyeball-searing bright comets we all look forward to. Instead, it is a fairly small run-of-the-mill comet that will take a little finding with binoculars or a telescope.

The comet itself was discovered as long ago as 1868 by Horace Tuttle, but was twice lost and then found again after long intervals by Giacobini and Kresak, hence its triple-barrelled name. It is in an orbit that takes it out just beyond the orbit of Jupiter and then brings it in to just beyond Earth’s orbit. It so happens that this year the Earth is in a good position to see its closest approach to the Sun, as the diagram here from JPL shows (click to enlarge). Even at its closest, on 1 April would you believe, it will be far too distant to affect Earth (despite what you might read on some websites where fake news gets clicks).

You can see 41P for yourself by using our map of Ursa Major (below). Click for a much larger version that shows stars down to magnitude 8, produced using SkyMap. You’ll find the constellation fairly high up in the north-eastern part of the sky, with the handle of the Plough pointing downwards. You will need a good, clear sky as dark as you can get. City observers should head for a darker area if possible. At around magnitude 7.5 41P is comparatively bright, but the fuzzy nature of comets can make them tricky to see where there is light pollution. If you have a choice of binoculars, use higher rather than lower magnification. 10 x 50s might be good enough in a dark sky but 15 x 70s are preferable. This comet is more of a photographic than a visual target from the UK.

Observing from Portslade in Sussex on March 21, Mike Feist could just see the comet with averted vision using a 65 mm spotting scope x 31. This indicates that in most UK skies, the comet is currently a tricky object. However, during the first week in April it is predicted to be about half a magnitude brighter than at present. 

Highlight of the event will come on 22 March when the comet passes close to two well-known features, the Owl Nebula (M97) and the galaxy M108. These can be seen in good skies with binoculars, but suitably equipped astrophotographers should be able to capture the image with a DSLR or CCD camera. Unfortunately for UK observers, the closest approach of the comet to M108 occurs at around 2 pm on the 22nd. However, the three objects will still be within close quarters on the morning or evening of the 22nd.

Comet 41P with M97 and M108

Comet 41P (lower right) with the star Merak (top), M97 and M108 (left), photographed with a 135 mm lens on March 20 by Stuart Atkinson. Click to enlarge.

Our Comet Section Director, Stuart Atkinson, has written a more detailed account of Comet 41P on our Facebook page. If you observe or photograph the comet, please do drop him a line at to tell him what you saw.

Positions for comet 41P during March 2017. Click for a larger and more detailed version. Ticks are for 0h UT on the day in question, so bear in mind that in the evening the comet will be closer to the next day's tick.


Added by: Robin Scagell