Astrophotography
Imaging Comet 46P/Wirtanen.
Comet 46P/Wirtanen has been difficult to see from the UK for the past few weeks because of its low southerly declination. That changes in December as the comet streaks north from Eridanus into Cetus, via Taurus, Perseus and Auriga before ending up in Lynx on New Year’s Eve.
Wirtanen’s December journey will have the comet travelling a total distance of approximately 95° over 31 days taking it past some photogenic deep-sky backdrops – the Hyades and Pleiades open clusters in Taurus mid-month, then NGC 1499, the California Nebula, before heading for a close encounter with Capella (Alpha (_) Aurigae) on 23/24 December.
All but the Capella encounter have a reasonable distance between their
deep-sky backdrops, so wide-field set-ups will be necessary to capture these photo opportunities. A typical setup will comprise a DSLR camera fitted with a standard photographic lens. Tracking will extend exposure times but non-driven setups should also be capable of recording the comet and the surrounding objects without trailing, so long as exposures are kept relatively short.
At the time of writing, the jury is out as to how bright Wirtanen will get. A peak above mag. 4.0 could be on the cards and if this does occur it begs the question as to whether it’ll be bright enough for less conventional imaging techniques. One interesting opportunity would be the possibility of recording the central coma region, which lies close to the nucleus, using a planetary imaging camera. With a large image scale and lucky imaging techniques, it may be possible to reveal details in the coma not obvious in wide-angle shots, such as dust jets.
The apparent speed of the comet relative to the stars beyond will present additional imaging opportunities. For example, with a tracking setup it will be possible to take sequential images of the comet and add them together in a short movie sequence. This may reveal the faint detail associated with the comet’s head and tail, something that can get lost in still images. If nothing else, a comet moving against the background stars is quite an impressive thing to record and show.
This technique has its own challenges. Equatorially tracked setups may start to record motion blur as the comet moves northeast through the constellations. Autoguiding on the head of a faint comet can be a tricky thing to pull off but in the case of 46P/Wirtanen, the nucleus region may, fingers-crossed, be bright enough for this to work. This will help to reveal any fainter detail present within 46P/Wirtanen, and potentially provide a very important scientific record of its passage.
However you decide to image it, the passage of a naked eye-bright comet at a decent altitude, soaring across the dark December skies in the UK is something to get excited about.
Send your images to: hotshots@skyatnightmagazine.com