Galaxy of the Month in Delphinus

• 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

• August 2013 - Galaxy of the Month

  NGC 6928 Group of Galaxies in Delphinus

  

  Image Courtesy of Jim Shuder, USA. Click on image for a high resolution version. For more images from Jim Shuder please visit his website. We have a Megastar© finder chart of NGC 6928. You may also be interest in this extract of Victor van Wulfen's 'Clear Skies Observing Guide' for NGC6928/NGC6930

  Summer is not thought of as galaxy season but even within classic Milky Way constellations such as Delphinius there are some galaxies.

  NGC 6928 could be thought of as a galaxy so good it was discovered twice. First seen by Albert Marth using William Lassell’s 48" speculum reflector from Malta it was catalogued as NGC 6928. Later it was independently rediscovered by Lewis Swift and catalogued as IC 1325. However there were still some errors and occasionally NGC 6928 is referred to as IC 1326, whereas that number in fact belongs to NGC 6930.

  There is a small group of galaxies associated with NGC 6928 and it would appear that 3 of them were found by Marth and given NGC numbers (6927, 6928 and 6930) and then the two brighter ones later found by Swift and given IC numbers. It appears that Swift processed his positions incorrectly and reversed the declination sign so they were not immediately associated with Marth’s discoveries.

  NGC 6828 itself is an edge on spiral galaxy classified as SBab. There appear to be 4-5 galaxies in the group and the group is known as WBL 663 from a paper on nearby poor clusters of galaxies.

  The galaxies in the group are relatively faint so a 30cm or larger telescope may be required to see the brighter ones, although 22cm can show NGC 6928 itself. It will however be faint in that aperture. The NGC galaxies are NGC 6928, NGC 6927, NGC 6927A and NGC 6930. There are a number of other fainter galaxies in the field as well with one right off the top of NGC 6930 making it appear like an exclamation mark. This galaxy was too faint to be seen by the NGC compilers but has a UGC number (11590).

  NGC 6927A was not a name given by the Dreyer but was a moniker given by the compilers of the RNGC who gave additional names to galaxies found on the POSS near other NGC galaxies. It would appear that probably a 45cm aperture will be needed to see NGC 6927 and that from very transparent skies.

  Observations with an 18" suggest that although 6928 and 6930 were visible 6927 was too difficult. The group is in the Atlas of Galaxy Trios by Miles Paul published by the Webb Society and is also to be found in the Atlas of Galaxy Trios downloadable from Alvin Huey’s website . There are a number of other faint galaxies in the field which are listed in the PGC or MAC catalogues but these are more likely targets for imagers.

  Owen Brazell - Galaxy Section Director