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Wed, 17 May 2017


A supernova and a comet


The supernova (arrowed) in NGC 6946, photographed on 16 May remotely from New Mexico by Robin Scagell

For the keen observers among you, there are two objects currently visible in evening skies to test your skills on. One is a supernova in a comparatively nearby galaxy, NGC 6946 in Cepheus, while the other is a comet, Comet Johnson, which is in Boötes.

   Neither of them are spectacular, so don’t hope to dash out with binoculars and spot them. The supernova is around 12th magnitude, which in theory is visible using a 150 mm telescope, but you need to know where to look. It’s probably more of interest to imagers equipped with CCDs on their telescopes. The comet is brighter, at around 8th magnitude, and has been seen by SPA members using small telescopes rather than binoculars.

finder chart for SN and comet  

Where to find NGC 6946 (lower left) and comet (upper right) on 17 May. Looking east about 11 pm BST

Supernova in NGC 6946

This was discovered by Patrick Wiggins of Utah on 14 May using a 350 mm reflector. The galaxy NGC 6946 has produced more supernovae than any other galaxy and has been called the ‘Fireworks Galaxy’ as a result. It is located in Cepheus, not far from Alpha Cephei, Alderamin, and near the border with Cygnus. It is circumpolar but is easily accessible after nightfall during May and June evenings.

A spectrum shows it to be a Type II supernova about a week before maximum light. These are caused by exploding supergiant stars, rather than white dwarf binary explosion.

Use the finder chart below, which shows stars to 10th magnitude, to star-hop from Alderamin to NGC 6946. Click for a larger printer-friendly version.

Finder chart for NGC 6946

Comet Johnson C/2015 V2

Comet Johnson
Comet Johnson, photographed with a five-minute exposure throuhgh a 150 mm refractor in New Mexico on 17 May. Robin Scagell

Discovered in November 2015, this comet is now well placed in the night sky crossing the kite shape of Boötes. While it is said by some sources to be 7th magnitude, in average UK skies it seems to be rather difficult to observe. Using a 25 x 52 spotting scope, Mike Feist of Portslade near Brighton found on 29 April that the comet was “visible as a rather faint fuzzy spot. When I compared this image to that of the globular cluster M56, in Lyra (and 8th magnitude), the cluster was more distinct and easier to see than the comet. “

The finder chart below shows the track of the comet during the second half of May and the first half of June. The comet’s brightness is not predicted to change substantially so you have a chance to wait for the best conditions, but as it is moving southwards the earlier the better.

Track of comet

Finder chart for C/2015 V2 Johnson for mid may to mid June 2017 through Boötes, produced using SkyMap. Stars shown to magnitude 8.5 Click to enlarge

Gallery

Comet Johnson

Comet Johnson photographed on 23 May at 23.42 UT through an 80 mm refractor. The stars immediately above and to the right of the comet are magnitude 10.

NGC 6946 with supernova, photographed on 24 May using an 80 mm refractor. Both images by Robin Scagell from Flackwell Heath, Bucks, using Atik 314L+ camera. The star immediately above the supernova is magnitude 12.85.

NGC 6946

NGC 6946 (lower left) and NGC 6939 (upper right). 2017 May 26, 80 mm ED refractor, Atik 314L+ camera, 28 x 30 sec L, 12 x 30 sec bin2 R, 13 x 30 sec bin2 G, 14 x 30 sec bin2 G. Total exposure time 33½ min. Robin Scagell

31 May. Stuart Atkinson writes: 'Comet V2 Johnson photographed from Kendal Castle around 1am this morning... best I could do with a processed stack of 20x30s tracked exposures through a 300mm lens, whilst fighting lingering twilight, high haze, light pollution, rising smoke from a campfire lit in the castle by half-drunk teenagers and their torches swaying around the sky like the heat rays of martian war machines looking for victims..!'

 

Added by: Robin Scagell