# Messier 91

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{{Short description|Galaxy in the constellation Coma Berenices}}
{{Infobox Galaxy
| name = [Messier](/source/Messier_object) 91
| image = M91 wfc3 4 crop v2 final.jpg
| caption = Spiral Galaxy Messier 91 imaged by the [Hubble Space Telescope](/source/Hubble_Space_Telescope)
| credit =
| epoch = [J2000](/source/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](/source/1_E23_m) [Mly](/source/light-year) (19 ± 5 [Mpc](/source/parsec)){{r|tonryetal2001}}
| z = 486 ± 4 km/[s](/source/second)<ref name="ned" />
| appmag_v = 10.2{{r|sedsm91}}
| size_v = 5.4{{prime}} × 4.3{{prime}}<ref name="ned" />
| size = 32.36 [kpc](/source/kiloparsec) (105,500 [ly](/source/Light-Year)) (estimated)<ref name = ned/>
| constellation name = [Coma Berenices](/source/Coma_Berenices)
| notes =
| names =  [NGC](/source/New_General_Catalogue) 4548,<ref name="ned" /> [UGC](/source/Uppsala_General_Catalogue) 7753,<ref name="ned" /> [PGC](/source/Principal_Galaxies_Catalogue) 41934<ref name="ned" />
}}

'''Messier 91''' (also known as '''NGC 4548''' or '''M91''')<ref name="WillW" /><ref name="SEDS" /> is a [barred spiral galaxy](/source/barred_spiral_galaxy) that is found in the south of [Coma Berenices](/source/Coma_Berenices). It is in the [local supercluster](/source/Virgo_Supercluster) and is part of the [Virgo Cluster of galaxies](/source/Virgo_Cluster). It is about 63 million [light-years](/source/light_year) away from [our galaxy](/source/Milky_Way). It was the last of a group of eight "[nebula](/source/nebula)e" &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](/source/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](/source/astronomer) William C. Williams{{r|WillW}} realized that M91 was NGC 4548,{{r|SEDS}} which was catalogued by [William Herschel](/source/William_Herschel) in 1784. Some sources contend the nearby spiral galaxy [NGC 4571](/source/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](/source/Messier_58),{{r|SEDS|UT}} where in fact it should have been [Messier 89](/source/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](/source/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](/source/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](/source/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](/source/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](/source/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

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Adapted from the Wikipedia article [Messier 91](https://en.wikipedia.org/wiki/Messier_91) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Messier_91?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.