NGC 938 Group of Galaxies in Aries

October 2017 - Galaxy of the Month

The group of galaxies around NGC 938 in Aries, (including NGC 932 and NGC 924), has an interesting discovery history and the usual NGC confusing identity conundrums.

NGC 932 was first discovered by William Herschel in 1785, however in 1872 Ralph Copeland observing with the 72” at Birr thought he saw another object just north of the main galaxy which was entered into the NGC as number 930.

Unfortunately there is nothing at Copelands position, but the identities of NGC 930 and NGC 932 became confused and the bright galaxy has, for some reason, has been referred to as NGC 930 for the last 100 years or so even though it is correctly catalogued as NGC 932. There is nothing at the position that Copeland gave for NGC 930. Most modern databases and star charting programs unfortunately refer to NGC 932 as NGC 930.

Herschel also found NGC 924 but missed NGC 938 and that was discovered by D’Arrest in 1863.

The group is also classified as LGG 61. The LGG catalogue counts 11 galaxies in the group also including the NGC galaxies 935 and 976. There are 9 other galaxies that are also included in this grouping but the others will be much fainter.

The three core galaxies should fit in a medium power field of view using a modern hyperwide eyepiece as they are separated by perhaps 30’.

If we use the historically correct designation then NGC 932 is interesting because there are several faint knots seen which are actually background galaxies seen through the disk, whether these can be seen except with the very largest telescopes in amateur hands is debatable.

NGC 932 itself is a classic face on spiral with a prominent nucleus and two blue spiral arms. These are likely to be too faint to be seen with normal amateur telescopes.

The core group consists of one each of the three main galaxy types. NGC 938 is classified as an elliptical, NGC 932 as a Sa spiral and NGC 924 as an S0, a lenticular.

The main group is perhaps 60 Mpc from us. The other two NGC galaxies in the group are quite a distance away on the sky from the main core as shown in the chart.

IC1797 and IC1801 are also part of the group with IC1801 making a nice pair with NGC 935. NGC 935 is also classified as Arp 276, an interacting system. It has been suggested that they are in the early stages of the collision. NGC 935 was found by Lewis Swift but it took Javelle with a 30” to find IC 1801 so this again is likely to be one for owners of large telescopes.

Owen Brazell - Galaxy Section Director