NGC 7331 – Wide Field

Key Scientific Data

Object type: Unbarred spiral galaxy – SA(s)b

Constellation: Pegasus

Other designations: Caldwell 30, UGC 12113, PGC 69327

Distance from Earth: approximately 45–50 million light-years

Diameter: approximately 120,000 light-years

Apparent size: approximately 10.5′ × 3.7′

Apparent magnitude: approximately 9.5–10.4, depending on the photometric band

Inclination: approximately 75–77°

Right Ascension: 22h 37m 04s

Declination: +34° 25′

Discovered by: William Herschel, 1784

Nucleus: Hosts a supermassive black hole

Light-travel time: approximately 45–50 million years

Description

NGC 7331 is a large spiral galaxy approximately 45–50 million light-years away, comparable in size to the Milky Way.

Its highly inclined disc reveals a prominent central bulge, dark dust lanes and spiral arms populated by young stars. The yellowish central region is dominated by older stellar populations, while bluish structures and small reddish emission regions trace ongoing star formation.

This wide-field image, captured with the William Optics RedCat 51 III WIFD, places NGC 7331 within an extensive extragalactic landscape containing numerous distant galaxies.

A Twin of the Milky Way?

NGC 7331 is sometimes described as a twin of the Milky Way because of its comparable size and spiral structure.

However, unlike our barred spiral galaxy, NGC 7331 is classified as an unbarred spiral, offering an external perspective on a broadly similar galactic system.

Curiosities

Discovered by William Herschel in 1784, NGC 7331 contains an unusual counter-rotating stellar component within its central region, possibly associated with past gravitational interactions or accretion events.

Its apparent proximity to several smaller galaxies also illustrates the importance of perspective when interpreting astronomical images.

A Field Full of Galaxies

The wide field includes the Deer Lick Group, comprising NGC 7331 and the apparently neighbouring NGC 7335, NGC 7336, NGC 7337 and NGC 7340.

Despite their apparent proximity, these smaller galaxies lie hundreds of millions of light-years farther away, making the group primarily an optical alignment rather than a gravitationally bound system.

The image also captures Stephan's Quintet, where four galaxies at approximately 280–300 million light-years are undergoing strong gravitational interactions. The fifth apparent member, NGC 7320, is a foreground galaxy approximately 40 million light-years away.

Beyond these prominent groups, dozens of faint PGC galaxies populate the field, appearing as tiny diffuse or elongated structures among foreground Milky Way stars.

Together, these objects reveal an extraordinary range of galactic distances and structures within a single photograph.

Looking Back in Time

The light captured from NGC 7331 began its journey approximately 45–50 million years ago, during Earth's Eocene epoch.

At that time, Earth was considerably warmer than today, tropical forests extended into higher latitudes, and early mammals, including ancestors of horses, whales and primates, were evolving. Humans had not yet appeared, and the earliest hominins were still tens of millions of years away.

The distant members of Stephan's Quintet reveal an even earlier period, approximately 280–300 million years ago, during the late Carboniferous to early Permian. Vast forests, giant insects and early reptiles inhabited Earth, while the supercontinent Pangaea was forming. Dinosaurs would not appear for another 50 million years or more.

This wide-field photograph brings together galaxies whose light began travelling towards Earth during profoundly different chapters of our planet's history.

Image Data

Total integration time: 19h

Integration by filter:

  • L-Pro: 4h 40m (56 × 300")

  • Red: 4h 33m 20s

  • Green: 5h 13m 20s

  • Blue: 4h 33m 20s

Equipment:

  • Telescope: William Optics RedCat 51 III WIFD

  • Camera: ToupTek ATR2600M

  • Mount: 10Micron GM2000 HPS II

  • Filters: Optolong L-Pro, Red, Green, Blue 2"

  • Accessories: ToupTek AAF Electric Focuser, WandererAstro WandererCover V4-EC

  • Software: Adobe Photoshop, Pleiades Astrophoto PixInsight, Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA)

For further information and the full-resolution image, visit AstroBin:

NGC 7331 – Wide Field – AstroBin