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Cosmic Challenge: NGC 51 Galaxy Group

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Cosmic Challenge: NGC 51 Galaxy Group


December 2023

Phil Harrington

This month's suggested aperture range:

12-inch (30.5-cm) and larger telescopes











NGC 51 group

Galaxy group

00h 14.2m

+48° 12.1’





Andromeda, the Princess, is best known to deep-sky observers for M31, the Andromeda Galaxy. But the princess also plays host to many other island universes, including this months challenging galactic menagerie.


Above: Early evening star map showing the location of this month's Cosmic Challenge.


Credit: Map adapted from Star Watch by Phil Harrington


Above: Finder chart for this month's Cosmic Challenge.


Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window


Of the dozens of galaxy groups scattered around the autumn sky, the 136-million-light-year-distant NGC 51 group is one of the more difficult bunches to spot.  Although they are not listed among Paul Hickson's compact galaxy groups, the six galaxies here are ideally placed near the zenith in early December evenings for observers at mid-northern latitudes.  Its high altitude carries the group far enough above any horizon-hugging interferences that might spoil some of our other challenges.  The table below lists the particulars of all six galaxies found here.


Members of NGC 51 Galaxy Group





Size (')

IC 1534

00h 13.8m

+48° 09.1



IC 1535

00h 13.9m

+48° 09.5



NGC 48

00h 14.0m

+48° 14.1



IC 1536

00h 14.3m

+48° 08.6



NGC 49

00h 14.4m

+48° 14.8



NGC 51

00h 14.6m

+48° 15.4




To locate this distant galactic swarm for yourself, first center your attention on 5th-magnitude 22 Andromedae in north-central Andromeda. Moving 2° to its north-northeast brings an optical double star made up of 6th- and 8th-magnitude components into view.  From here, you are only minutes away (minutes of arc, that is) from the challenge, as the galaxies lie about 20' to the stars' east.


A string of three NGC galaxies highlights the sextet.  All were discovered in 1885 by American astronomer Lewis Swift through a 16-inch (40.6-cm) refractor.  The easternmost of the trio is the lenticular galaxy NGC 51.  Most find this to be the brightest and easiest of the bunch to spot, although it can still be tricky at magnitude 13.1.  Its slightly oval disk is punctuated by a brighter central core, making it possible to glimpse NGC 51 through 10-inch (25-cm) telescopes under excellent sky conditions.


Above: The NGC 51 Galaxy Group, as seen through the author's 18-inch (46.7-cm) reflector. (South is up.)

Below: NGC 51 and company. (North is up.) Credit: Donald Pelletier, via Wikimedia Commons.


Can you spot a second, dimmer smudge 2' to the west of NGC 51?  If so, you have seen 14th-magnitude NGC 49.  Look for a small, slightly oval blur with a brighter stellar nucleus that becomes evident by using averted vision.  The sketch above was made on a better-than-average suburban night with my 18-inch (46-cm) reflector.


NGC 48 is a third faint fuzzy another 3½' further west of NGC 49.  Although NGC 48 is also rated at 14th magnitude, the larger apparent size of this S(B)pc peculiar barred spiral causes its surface brightness to drop, hampering detection.  It displays a faint stellar core surrounded by an even dimmer galactic halo that appears slightly elongated southwest-northeast through my 18 inch at 171x.


The other three galaxies in the group, discovered by Edward Barnard in 1888, all shine on the low side of 14th magnitude.  IC 1534 is seen only as an extremely faint, elliptical glow about 5' southwest of NGC 48.  Careful scrutiny with 200x or so might show its tiny disk brightening to a central core.  A faint star just kisses the northeastern edge of IC 1534.


IC 1535 trails close behind.  This apparently coreless galaxy is also oval, but oriented perpendicular to IC 1534.  It is also larger and fainter, making it a difficult test indeed.


The final galaxy, IC 1536, looks almost perfectly round.  Look for its tiny smudge of gray light along the southern side of a triangle of three 13th-magnitude stars.

Do you have a favorite challenge object of your own? I'd love to hear about it, as well as how you did with this month's test. Contact me through my website or post your observations/suggestions in this month's discussion forum.


Until next year, remember that half of the fun is the thrill of the chase. Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy. Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2023 by Philip S. Harrington.  All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


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