Spiral Galaxy NGC 7331, and ‘the Fleas’ Copy Copy

October 2021 Spiral Galaxy NGC 7331, and ‘the Fleas’ Copy Copy

Target	Type	R. A.	Dec.	Constellation	Magnitude	Size
NGC 7331 (Caldwell 30)	Spiral Galaxy	22h 37m 04s	+34° 24′ 56″	Pegasus	9.25	9.3 x 3.8 arcmins

Overview

The main galaxy we’re hunting for in this challenge is a large oval galaxy with a bright center. What’s not mentioned in the table above are the four ‘fleas’ that we can also tour while spending time in this neighborhood. They’re known as the fleas thanks to the horse constellation – Pegasus – which they reside in.

That they all appear to be near each other is an optical illusion. NGC 7331 is the brightest and largest of the five galaxies in part because it is the closest of them all, ‘only’ 47 million light-years away.

Also known as the ‘deer lick group’, the bright main galaxy has four attendant galaxies on its eastern side. In catalog order, they are:

NGC 7335 – Mag 13.4, 310 million light-years away
NGC 7336 – Mag 15.6, 430 Mly away
NGC 7337 – Mag 15.6, 520 Mly away
NGC 7340 – Mag 14.6, 310 MLY away

You can see that the four ‘fleas’ are very dim and will present a possibly insurmountable challenge in a smaller scope under light-polluted skies. So, we’ll treat these four as a bonus to the main show (NGC 7331), which, at magnitude 9.25, is easily spied in smaller instruments and dark skies. Even decent, stably mounted binoculars will reveal it under good seeing conditions.

We see NGC 7331 nearly edge-on, so it looks long and slender in your eyepiece. This spiral galaxy is believed to be similar to our own Milky Way and extends to 30,000 light-years wide.

Finder Charts

We begin by locating the general area of sky to hunt in. The first image below is 22:00 at the end of the first week of October. For clarity, the Moon and planets are not shown, stars are shown to magnitude 5.0 only.

Note the Great Square of Pegasus high in the eastern sky. NGC 7331 is near Lacerta and circled in orange.

[NGC7331-1] Our galaxy is near the zenith in mid-October evenings. Click for full-screen.

When you have Pegasus and Lacerta fixed, identify the stars Matar and 6 Lacertae (shown on the SkySafari 6 image below) and connect the two with an imaginary line. NGC 7331 is 4° along that line, or about a third of the way, from Matar.

[NGC7331-2] Find the galaxy using the stars Matar and 6 Lacertae. Click for full-screen.

When you have NGC 7331 in your eyepiece, which will be apparent as a blurry apparition, swap out to give some higher magnification. The image below shows the main galaxy and the four ‘fleas’ all inside a 1/3° field of view (blue ring).

[NGC7331-3- The main galaxy with the four ‘fleas’ to the east. Click for full-screen.

Now you have it in view, what should you expect to see?

Individual Telescope Views

The following views will help you find NGC 7331 in different telescope types by presenting the images as your telescope will show them. The first image is with a black sky and white stars, the second picture is the same image but presented in inverse monochrome. Black stars on a white background is often easier to use at the telescope. Each image can be clicked on for a full-screen version.

Upright View – This is what your eyes see unaided and through a reflex or red-dot finderscope

Upside-down view – This is what reflectors and magnifying finders show, and refractors / Cassegrains without a star diagonal

Mirrored View – Refractors and Cassegrain models with a star diagonal show this view

Observation

The main galaxy, NGC 7331, is a relatively easy target. In a 4″ scope at low magnification, around 50x, you will see it if your sky is dark enough. A larger aperture reveals more detail at higher magnification. See if you can note the difference in light fall off between its two sides. The more abrupt loss of light on its western edge indicates the presence of a dust lane there.

This is a large galaxy and, with careful study, you should be able to see the brighter core of stars at its heart.

The companion galaxies are much smaller and dimmer, but all happily coexist in the same small field of view. You’ll only see the faintest of them with averted vision, and even then you’ll need a dark sky and good optics. NGC 7335 is the easiest of the four to spy. We can glimpse the uniform grayness of its core but no extended details.

Enjoy tracking down this little galactic cluster and ticking off the fleas.

Each of the star maps above is reproduced as a pdf below. Each star map has a number in [square brackets] beneath it which corresponds to the file number below. If you want image [NGC7331-1], for example, click the ‘download’ button next to it below and you’ll be able to open it as a printable pdf.