Messier 51 is one of the most famous and photogenic galaxies in the night sky, renowned for its striking spiral arms and its dramatic interaction with its smaller companion, NGC 5195. The galaxy is a favorite among astrophotographers due to its high surface brightness and the wealth of detail visible even with moderate equipment. Its distinctive structure can be captured with anything from a DSLR and telephoto lens to advanced cooled cameras and large telescopes, with longer exposures revealing faint tidal features and subtle color variations. M51’s historical significance is notable as it was the first galaxy where spiral structure was identified, and it continues to inspire both visual observers and imagers today.
Names and Catalog numbers
- Whirlpool Galaxy
- Question Mark Galaxy
- Messier 51 (M51)
- NGC 5194
- PGC 47404
- UGC 8493
- ARP 85
Position and the cosmic neighborhood
Messier 51 is located in the constellation Canes Venatici, just southwest of Alkaid, the end star of the Big Dipper’s handle in Ursa Major. Its close proximity to NGC 5195, which appears to be merging with M51, creates a visually striking pair that stands out in both wide-field and high-magnification astrophotography. The galaxy lies in a region of the sky rich with other faint galaxies, offering additional targets for deep-sky imaging sessions. Its circumpolar position for much of the Northern Hemisphere means it never sets and can be imaged throughout much of the year, with the best results during spring.
Nice to Know
- M51 was the first galaxy where spiral arms were identified, a discovery made in 1845 by William Parsons.
- The galaxy is currently interacting with its companion, NGC 5195, leading to dramatic tidal features and bursts of star formation.
- Three supernovae have been observed in M51 since 1994, adding to its astrophysical interest.
- Astrophotographers have achieved stunning results on M51 with both short and extremely long integration times, with collaborative projects exceeding 500 hours of exposure revealing incredible detail.
Brightnes, distance and size
Messier 51 shines at an apparent magnitude of about 8.4, making it visible in small telescopes and even binoculars under dark skies, with its spiral structure becoming apparent in moderate to large apertures or long-exposure images. The galaxy is located approximately 23 million light-years from Earth and has a diameter of about 76,900 to 80,000 light-years. Its apparent size is roughly 11 by 7 arcminutes, making it a prominent and rewarding target for astrophotographers, especially when capturing the extended tidal features and its interacting companion.
