NGC 7331 is a remarkable spiral galaxy that has attracted attention for its size, structure, and resemblance to our own Milky Way. Located millions of light-years away in the constellation Pegasus, it is bright enough to be observed by experienced skywatchers with suitable equipment.
Yet despite its impressive qualities, NGC 7331 is not part of the famous Messier catalog. That raises an interesting question: if the catalog were created today, would this galaxy deserve a place in it?
A Large Spiral Galaxy
NGC 7331 is located approximately 45 million light-years from Earth. It was discovered by William Herschel in 1784 and later included in the New General Catalogue, commonly called the NGC.
Like many spiral galaxies, NGC 7331 has a bright central bulge surrounded by a broad disk containing spiral arms. Its structure makes it an interesting subject for studying how stars are distributed within a large galaxy.
From Earth, the galaxy appears at an angle that allows astronomers to examine its central region and surrounding disk. Observations have revealed differences in the ages and characteristics of stars across the galaxy, providing useful information about its development over time.
Similarities to the Milky Way
One reason NGC 7331 receives so much attention is its comparison with the Milky Way. Both are large spiral galaxies with substantial central regions and extended disks.
However, the similarities should not be taken too far. NGC 7331 is not an exact copy of our galaxy. Galaxies can have different histories, structures, and patterns of star formation even when they share a broad classification.
Studying a galaxy with several familiar characteristics gives astronomers another way to examine the processes that shape spiral galaxies. Instead of relying only on observations from inside the Milky Way, researchers can study a separate system from the outside and compare its properties with what is known about our home galaxy.
A Fascinating Neighborhood
NGC 7331 is also notable because of its location in a visually interesting region of the sky. Several other galaxies can be seen in the same general area, including the group commonly known as Stephan's Quintet.
Although these galaxies may appear relatively close together when viewed from Earth, they are actually located at different distances. This provides a useful reminder that a two-dimensional view of the sky can hide enormous differences in depth. For observers, this region offers an opportunity to see multiple distant galaxies within a relatively small part of the sky.
Why It Is Not a Messier Object
The Messier catalog has a very different origin from the modern astronomical catalogs used today. Charles Messier and Pierre Méchain compiled the original list during the 18th century, primarily to identify fuzzy objects that could be mistaken for comets.
NGC 7331 was discovered in 1784, after Messier's original catalog had already been completed. Because of this timing, it never received a Messier number. The absence of a Messier designation does not mean the galaxy is less important or less impressive. The Messier catalog is essentially a historical collection rather than a ranking of the best astronomical objects.
Does It Deserve Messier Status?
If the Messier catalog were being created from scratch today, NGC 7331 would certainly be an interesting candidate. It is relatively bright, large, structurally distinctive, and scientifically useful.
Still, there is no official modern process for adding new objects to the original Messier catalog. Its historical list remains unchanged, meaning NGC 7331 will continue to be identified by its NGC designation.
Calling it “Messier-worthy” is therefore more of an appreciation than an official classification. The phrase highlights how easily this galaxy could have become one of the famous names in amateur astronomy if history had unfolded differently.
NGC 7331 proves that a galaxy does not need a Messier number to stand out. Its large spiral structure, similarities to the Milky Way, and interesting surroundings make it a valuable subject for astronomy.
Its omission from the Messier catalog is mainly a matter of history and timing. Had the catalog been compiled differently, NGC 7331 might have become one of its best-known members. For now, this impressive spiral galaxy remains a fascinating deep-sky object in its own right.
