The Whirlpool Galaxy, also cataloged as Messier 51 and NGC 5194, is one of the most rewarding spiral galaxies for astrophotographers, presenting its swirling arms nearly face-on. At magnitude 8.36 and spanning 9.0′ × 7.8′, it is bright and large enough to yield detailed results even with modest apertures, while long integration times reveal the delicate dust lanes and the luminous companion galaxy tugging at one arm. Its surface brightness of 21.6074 mag/arcsec² means the fainter outer structure benefits from dark skies and patient exposure stacking. Broadband imaging captures the golden core and blue arms, and adding hydrogen-alpha data brings out the pink star-forming knots strung along the spiral pattern.
Names and Catalog numbers
- Whirlpool Galaxy
- M 51 (Messier 51)
- NGC 5194
- UGC 8493
- PGC 47404
- Arp 85
Position and the cosmic neighborhood
The Whirlpool Galaxy sits in the northern constellation Canes Venatici, close to the boundary with Ursa Major, at a declination of roughly +47°, which makes it a circumpolar or high-riding target for most northern observers. It can be conveniently star-hopped from the tip of the Big Dipper’s handle, a location that keeps it comfortably above the horizon for long imaging sessions through spring. In the frame, its interacting companion lies just to the north, and the pairing makes for a compelling wide-field composition that also allows generous room for framing against the surrounding star field.
Nice to Know
- It carries multiple catalog identities, including Messier 51, NGC 5194, Arp 85, PGC 47404, and UGC 8493, reflecting its long history of study.
- Its inclusion in the Arp Atlas of Peculiar Galaxies (as Arp 85) highlights the dramatic interaction with its companion, a favorite subject for imagers.
- Presenting almost perfectly face-on, it displays textbook grand-design spiral arms that photograph beautifully with even short focal lengths.
- With a physical diameter of about 68,600 light-years, it is a substantial galaxy whose full extent rewards deep, well-guided exposures.
Brightness, distance and size
The object has an apparent magnitude of 8.4 mag, it lies about 26.1 million light-years from Earth and spans roughly 68,600 light-years across. On the sky it appears about 9.0′ × 7.8′ in size.
