NGC 6956 in Delphinus

July 2023 - Galaxy of the Month

I apologise for the short GOM this month but galaxies are not easy to find from the UK in the summer. Our challenge this month is the faint galaxy NGC 6956 in Delphinus.

Discovered by William Herschel in 1784, NGC 6956 is a barred spiral galaxy that was recently imaged by the Hubble Space Telescope (HST) as part of a program to calibrate the distance scale. The Hubble observations allowed scientists to study the Cepheid variable stars in it and they, along with the Type Ia SN 2013fa, allowed scientists to work on the distance relationships. It has also hosted 2 other supernovae in the last 10 years as well.

NGC 6956 is thought to lie about 214 million light-years away. It is part of the isolated galaxy triplet known as KTG 71 and is also included in the galaxy group LGG 440, which includes NGC 6956 as well as UGC 11620 and UGC 11623. The galaxies appear to be physically associated but are not interacting at this time. Two of the galaxies appear to be barred spirals whilst the third is a lenticular. Perhaps unsurprisingly, apart from studies of the supernovae discovered in NGC 6956, not a great deal of work has been done on these galaxies. As these galaxies lie on the edge of the Milky Way the group suffers from quite a bit of extinction.

The group is very close together so a high-power eyepiece maybe best to use when the group is acquired. In theory all three should be in range of a 37cm telescope but I suspect that to pick up the fainter ones is going to require a 45cm or greater from UK skies.

The Night Sky Observer's Guide (NSOG) Vol. 2 suggest that a 16-18” telescope is required to see much of NGC 6956 but does not mention any observations of the two UGC galaxies. Steve Gottlieb does mention observations of them with his 24” at high altitude and says they are faint which suggests they are going to be out of reach of visual observers from the UK. Interestingly Luginbuhl and Skiff (L&S) suggest NGC 6956 can be seen with 25cm, although this may well have also been from high altitude. There are some observations of the group using an EAA type system. Observations in the UK made with a 40cm telescope suggest it is round and small and quite faint, although this was probably not from a good site. The group is also included in Alvin Huey’s galaxy trios booklet.

Owen Brazell - Galaxy Section Director