Messier 91, also cataloged as NGC 4548, is a barred spiral galaxy that presents a compact yet rewarding target for astrophotographers working the Coma Berenices region. At an apparent magnitude of 13.57 and with a fairly faint surface brightness of 25.5873 mag/arcsec², it demands dark skies and generous integration time to bring out its subtle bar and spiral structure. Its modest angular size of 5.2′ × 4.3′ makes it well suited to longer focal lengths, where the central bar and surrounding arms can be resolved with care. Careful stretching and noise reduction are key, as the galaxy’s low surface brightness can easily be lost against background sky glow in shorter exposures.
Names and Catalog numbers
- M 91 (Messier 91)
- NGC 4548
- UGC 7753
- PGC 41934
Position and the cosmic neighborhood
Messier 91 (NGC 4548) sits at right ascension 12h 35m 26.4s and declination +14° 29′ 47″ within Coma Berenices, placing it squarely in one of the richest regions of the sky for galaxy hunters. This part of the heavens overlaps the sprawling Virgo–Coma galaxy fields, so a single well-planned framing can often capture additional faint island universes scattered across the background. For imagers, this density of targets makes wide-field mosaics and multi-object compositions especially attractive, though it also calls for accurate plate solving to keep track of which faint smudge is which.
Nice to Know
- Messier 91 is one of the faintest objects in the entire Messier catalog, making it a genuine challenge that rewards patient, long-exposure astrophotography.
- The galaxy spans roughly 83,100 light-years across, a fairly compact disk that photographs best at longer focal lengths.
- It carries multiple designations — M 91, NGC 4548, PGC 41934 and UGC 7753 — reflecting its inclusion across several major sky surveys.
- Its radial velocity of 489 km/s corresponds to a redshift of just 0.00163246, consistent with its membership in the nearby Virgo Cluster region.
Brightness, distance and size
The object has an apparent magnitude of 13.6 mag, it lies about 54.5 million light-years from Earth and spans roughly 83,100 light-years across. On the sky it appears about 5.2′ × 4.3′ in size.
