NGC 7331 (Caldwell 30): The Milky Way’s Twin

NGC 7331, also known as Caldwell 30, is a galaxy in the constellation Pegasus, best viewed during autumn.

Before the 2000s, astronomers believed Caldwell 30 was like our own Milky Way due to its similar size and structure. However, Milky Way research has exposed some differences, including that we now believe our galaxy is a barred one, while Caldwell 30 is not. Essentially, barred galaxies have a bar structure made of stars embedded in the middle. Regardless of this dissimilarity, Caldwell 30 is a beautiful spiral galaxy in photos and gives us a nice glimpse of what we—somewhat—look like from more than 40 million light years away.¹ Backyard astronomers with a telescope can break through the mild light pollution to find Caldwell 30 looking like a faint smudge (see observation below).

Historically speaking, the astronomer William Herschel discovered the galaxy on September 5, 1784.

My Observations

The sky’s transparency is not so great tonight, so I look forward to returning to Caldwell 30 in the future. Even under these conditions, I can make out the “smudge” in my scope—and even see a slight centered bulge in the middle. Oh, to be on that side of the universe looking back at me, taking in God’s view.

Constellation	Pegasus
Best Viewing	Autumn
Visual Magnitude	+9.25
Absolute Magnitude	-21.56
Distance from Earth	40 million light yrs
Diameter	128,000 ly
Apparent Size	9.3 x 3.8 arcmin
Milky Way Location	NA
My Viewing Grade	B-
Designations	C 30, NGC 7331, UGC 12113

Sources and Notes

Banner photo of Caldwell 30: Adam Block/Mount Lemmon SkyCenter/University of Arizona. This file is licensed under the Creative Commons Attribution 3.0 Unported license.

¹ Henderson, Edward. “Caldwell 30.” NASA, NASA, 24 Nov. 2019, https://www.nasa.gov/feature/goddard/caldwell-30.

Sketch by Wayne McGraw