{{Short description|Galaxy in the constellation Coma Berenices}} {{Infobox Galaxy | name = Messier 91 | image = M91 wfc3 4 crop v2 final.jpg | caption = Spiral Galaxy Messier 91 imaged by the Hubble Space Telescope | credit = | epoch = J2000 | type = SBb(rs){{r|ned}} | ra = {{RA|12|35|26.4}}<ref name="ned" /> | dec = {{DEC|+14|29|47}}<ref name="ned" /> | dist_ly = 63 ± 16 Mly (19 ± 5 Mpc){{r|tonryetal2001}} | z = 486 ± 4 km/s<ref name="ned" /> | appmag_v = 10.2{{r|sedsm91}} | size_v = 5.4{{prime}} × 4.3{{prime}}<ref name="ned" /> | size = 32.36 kpc (105,500 ly) (estimated)<ref name = ned/> | constellation name = Coma Berenices | notes = | names = NGC 4548,<ref name="ned" /> UGC 7753,<ref name="ned" /> PGC 41934<ref name="ned" /> }}

'''Messier 91''' (also known as '''NGC 4548''' or '''M91''')<ref name="WillW" /><ref name="SEDS" /> is a barred spiral galaxy that is found in the south of Coma Berenices. It is in the local supercluster and is part of the Virgo Cluster of galaxies. It is about 63 million light-years away from our galaxy. It was the last of a group of eight "nebulae" &ndash; the term 'galaxy' only coming into use for these objects once it was realized in the 20th century that they were extragalactic &ndash; discovered by Charles Messier in 1781. It is the faintest object in the Messier catalog, with an apparent magnitude of 10.2.<ref name=sedsm91 />

As a result of a bookkeeping error by Messier, M91 was for a long time one of the few missing entries in the Messier catalog, not matching any known object in the sky. It was not until 1969 that amateur astronomer William C. Williams{{r|WillW}} realized that M91 was NGC 4548,{{r|SEDS}} which was catalogued by William Herschel in 1784. Some sources contend the nearby spiral galaxy NGC 4571 was considered as a candidate for this object by Herschel.<ref name="SEDS" />

==Observation history== The object was discovered in 1781{{efn|on March 18}} by Messier who described it as nebula without stars, fainter than M90. Messier mistakenly logged its position from Messier 58,{{r|SEDS|UT}} where in fact it should have been Messier 89. William Herschel observed the same object in 1784.{{efn|On April 8}}

In 1969 Williams solved this lost Messier object by measuring its right ascension and declination relative to those of the nearby galaxy M89 (notable reference stars angularly nearby are sparse) &ndash; rather than M58, a 9th-magnitude galaxy which Messier recorded in 1778. This amended night sky "star-hopping" reference point matches Messier's figures<ref name="WillW" /> to 0.1 of an arcminute ({{prime}}) in right ascension and 1{{prime}} in declination, a sixtieth of a degree. thumb|Location of M91

==Features== Inclusion of Messier 91 in the Virgo cluster was confirmed in 1997 from observing Cepheid variables which place it at {{val|52|6}} million light years away.<ref name="SEDS" />

Its bar is very conspicuous &ndash; it is seen with position angle of 65 to 245 degrees when being measured from the North direction to the East.<ref name="SEDS" />

There is a countering peculiar (local) velocity toward us through the Virgo cluster of about 700&nbsp;km/s within the cluster's recession velocity of about 1100&nbsp;km/s, which produces its observed recessional velocity of only about 400&nbsp;km/s.<ref name="SEDS" /> Another source gives the latter figure as 803&nbsp;km/s.{{r|VC}}

Messier 91 is also classified as an anemic galaxy, that is: a spiral galaxy with little star formation and gas compared with other galaxies of its type.{{r|Vollmer1999|Fumagalli2009}}

==See also== * List of Messier objects

==References and footnotes== <references>

<ref name="ned">{{cite web |website=NASA/IPAC Extragalactic Database |title=Results for object NGC 4548 |url=http://nedwww.ipac.caltech.edu/cgi-bin/nph-objsearch?objname=M+91&extend=yes&out_equinox=J2000.0 |access-date=2006-12-13}}</ref>

<ref name="tonryetal2001">{{cite journal |author=J. L. Tonry | author2=A. Dressler | author3=J. P. Blakeslee | author4=E. A. Ajhar | author5=A. B. Fletcher | author6=G. A. Luppino | author7=M. R. Metzger | author8=C. B. Moore | display-authors=4 |date=2001 |title=The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distance |journal=Astrophysical Journal |volume=546|issue=2|pages=681–693 |bibcode=2001ApJ...546..681T |doi=10.1086/318301 |arxiv = astro-ph/0011223 | s2cid=17628238}}</ref>

<ref name=sedsm91>{{cite web |url=https://messier.seds.org/m/m091.html |title=Messier 91 |access-date=30 April 2022 |website=SEDS Messier Catalog}}</ref>

<ref name=WillW>William C. Williams [http://messier.seds.org/xtra/history/williams69.html Letter], Sky and Telescope, December 1969, p. 376. Accessed 13 April 2011</ref>

<ref name=SEDS>Students for the Exploration and Development of Space [http://messier.seds.org/m/m091.html Messier 91], Accessed online 14 April 2011</ref>

<ref name=UT>{{cite web|title=Messier 91|url=http://www.universetoday.com/48349/messier-91/|work=University Today|access-date=2010-04-14}}</ref>

<ref name=VC>[http://www.atlasoftheuniverse.com/galgrps/vir.html Virgo cluster]</ref>

<ref name=Vollmer1999>{{cite journal |last1=Vollmer |first1=B. |last2=Cayatte |first2=V. |last3=Boselli |first3=A. |last4=Balkowski|first4=C. |last5=Duschl |first5=W.J. |date=1999 |title=Kinematics of the anemic cluster galaxy NGC 4548. Is stripping still active? |journal=Astronomy and Astrophysics |volume=349 |pages=411–423 |bibcode=1999A&A...349..411V |arxiv = astro-ph/9907351}}</ref>

<ref name=Fumagalli2009>{{cite journal |last1=Fumagalli |first1=M. |last2=Krumholz |first2=M.R. |last3=Prochaska |first3=J.X |last4=Gavazzi |first4=G. |last5=Boselli |first5=A. |date=2009 |title=Molecular Hydrogen Deficiency in H I-poor Galaxies and its Implications for Star Formation |journal=The Astrophysical Journal |volume=697 |issue=2 |pages=1811–1821 |bibcode=2009ApJ...697.1811F |doi=10.1088/0004-637X/697/2/1811 |arxiv = 0903.3950 |s2cid=17561429}}</ref>

</references>

{{notelist}}

==External links== {{commonscat}} * [http://messier.seds.org/m/m091.html SEDS: Messier Object 91] * [https://web.archive.org/web/20140531104753/http://www.astrodwarf.com/deep-sky/detail/2593 Galaxy M91] *{{WikiSky}}

{{Sky|12|35|26.4|+|14|29|47|63000000}} {{Portal bar|Astronomy|Stars|Outer space}} {{Messier objects}} {{Ngc50}} {{Coma Berenices}}

Category:Barred spiral galaxies Category:Virgo Cluster Category:Coma Berenices 091 Category:NGC objects 07753 41934 Category:Astronomical objects discovered in 1781 Category:Discoveries by Charles Messier