NGC 797 in Andromeda
November 2025 - Galaxy of the Month
For this month challenge I have gone with the galaxy pair in Andromeda, NGC 797 and NGC 801.
NGC 797 was discovered by William Herschel in 1786. He missed the nearby edge on spiral NGC 801 which was discovered nearly 100 years later by Lewis Swift in 1885. There is some confusion over the identification of the object found by Swift but as this is the only nearby object it gets the nod.
NGC 797 is a barred spiral galaxy lying about 113 Mpc away. NGC 797 and NGC 801 form a physical pair with the distance between them being about 150 kpc.
In his Catalogue of Selected Compact Galaxies and of Post-Eruptive Galaxies Fritz Zwicky found a compact companion on the edge of one of NGC 797’s spiral arms and thought they were associated. There are some question marks over their connection and it maybe that they are purely a line of sight coincidence. The spiral arm in the direction of the compact galaxy does however show some signs of interaction so perhaps they are a pair.
NASA/IPAC Extragalactic Database (NED) as well as SIMBAD suggest there is a galaxy pair here but I am not sure if they are referring to the NGC 797/801 pair or the NGC 797/LEDA 212899 pair. The NGC 797/LEDA pair is also listed as number VV 478 in the Vorontsov-Velyaminov catalogue of interacting systems where he suggests it is a system of the M51 type. LEDA 212899 is also known as NGC 797b but there is not much else published on it.
A type Ia supernova was discovered in NGC 797 in 2025 (SN 2025pel)
NGC 801 is an edge on spiral galaxy with a suspected AGN of the LINER type. It is very much fainter than NGC 797 which is probably why Herschel missed it, even Swift thought it was faint with a 16” refractor. It is classified as an Sc type system seen almost edge on and there are obvious dark lanes in images, similar to those seen in NGC 891.
Both of these galaxies are quite close together and should fit in the same medium power field of view. Perhaps as expected given their faintness they are not in any of the common deep sky lists. The small companion to NGC 797 is listed as 16th magnitude so it may be in the range for large amateur telescopes. The Night Sky Observer's Guide (NSOG) Vol. 1 suggests that NGC 797 is faintly visible in 14” telescopes but more is seen with 16/18” telescopes. No mention is made in the NSOG of NGC 801 or the companion to NGC 797. Steve Gottlieb in his notes suggests that NGC 797 is moderately bright in 17.5” but NGC 801 is faint but again does not note the companion to NGC 797.
Owen Brazell - Galaxy Section Director
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Galaxy of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
