Messier 91 (also known as NGC 4548 or M91)[4][5] is a barred spiral galaxy that is found in the south of Coma Berenices.

It was the last of a group of eight "nebulae" – the term 'galaxy' only coming into use for these objects once it was realized in the 20th century that they were extragalactic – discovered by Charles Messier in 1781.

Some sources contend the nearby spiral galaxy NGC 4571 was considered as a candidate for this object by Herschel.

This amended night sky "star-hopping" reference point matches Messier's figures[4] to 0.1 of an arcminute (′) in right ascension and 1′ in declination, a sixtieth of a degree.

Inclusion of Messier 91 in the Virgo cluster was confirmed in 1997 from observing Cepheid variables which place it at 52±6 million light years away.