M91
ILLUSTRATION FROM HUBBLE TYPE Sb · SURFACE BRIGHTNESS 23.2 MAG/ARCSEC² · MAJOR AXIS 5.55′ · AXIS RATIO 0.81 · POSITION ANGLE 150°
OVERVIEW
] GALAXYM91 is a spiral galaxy Sb in the constellation Coma Berenices, 38.01 from Earth, shining at apparent magnitude 10.96 (). It is catalogued as 2MASX J12352642+1429467, IRAS 12328+1446 and IRAS F12329+1446, among 10 designations in total. It was discovered in 1781.
- WHAT IT IS
- Spiral galaxy
- HOW FAR
- 38.01
- HOW BIG ON THE SKY
- 5.5
- HOW BRIGHT (V)
The light arriving now left it that long ago.
Small enough that the full Moon would cover it several times over.
A small telescope reaches it.
OBSERVING
] FROM WHERE YOU AREWhat it takes to see M91 for yourself. Everything in this part of the page is worked out for a real horizon, a real night and the equipment you say you have.
Say where you are, and this line says when M91 is worth going out for.
THROUGH AN EYEPIECE
] 150 MM TELESCOPE · 25 MM EYEPIECEOut of reach of binoculars; a 150 mm telescope reaches it. M91 covers 5.5′ of sky against a of 1.08°, so at 48× it is a small patch, centred.
- 48×
- 1.08
- 1.25
- 13.0
- SIZE ON THE SKY
- 5.5
- FILLS OF THE FIELD
- 9% of the width
- APPARENT MAGNITUDE ()
- 10.96 · within reach
M91 is not a point of light, so the limit above is the wrong one to hold it against: the same brightness spread over 5.5′ of sky is harder than a star of it, and goes first — spread out, it comes to 23.2 . Catalogued sizes are measured to a photographic contour, and the part an eye sees is usually smaller.
APPARENT PLACE
] EQUINOX J2026.7Where a telescope has to be pointed today, which is not quite where the catalogue records the object: the coordinate grid itself has turned since the year 2000 the catalogue is referred to.
- RIGHT ASCENSION
- DECLINATION
- GRID TURNED SINCE
- 21.6
- PROPER MOTION SINCE
- none published
Computed for 2026-08-27 00:00 UT. No proper motion is published for M91, so nothing here moves the object; what separates this from the catalogued position above is the coordinate grid turning under it — about fifty arcseconds a year of precession since 2000, and the small nodding of the Earth’s axis on top of that. Aberration and refraction are not included, and neither is parallax; each is under an arcminute, which is also about as well as the catalogued position is known. The same figure for any date.
CATALOG DATA
] 17 FIELDSThe raw catalogue values, as the source published them, with the error bars where one was published — sorted by what each set of figures is about rather than by the order they happened to be stored in.
WHAT IT IS MADE OF
What the object is in itself, rather than how it happens to look from here.
- Hubble type
HOW BRIGHT IT IS
What the light adds up to, measured through one filter at a time. A magnitude is a brightness on a backwards scale — the smaller the number, the brighter the object.
- Apparent magnitude ()
- Apparent magnitude ()
- Apparent magnitude ()
- Apparent magnitude ( band)
- Apparent magnitude ()
- Surface brightness
- 23.24
WHERE IT IS AND HOW IT MOVES
Position, motion across the sky and the size it covers on it. These are measurements of the object as seen from here, so every one of them depends on where here is.
- Radial velocity
- 492
- Redshift (z)
- Redshift (z, CMB frame)
- Major axis
- 5.55
- Minor axis
- 4.52
- 150
WHEN IT WAS FOUND
Who first saw it, from where, and by what method.
- Discovered by
- Charles Messier
OTHER NAMES AND NUMBERS
The identifiers other catalogues file this object under, for anyone joining this data to theirs.
- OpenNGC type code
- G
- Wikidata item
- Q14344
- Wikipedia article
- Messier 91
ALSO KNOWN AS
] 10 DESIGNATIONS- 2MASX 2MASX J12352642+1429467
- IRAS IRAS 12328+1446
- IRAS IRAS F12329+1446
- LEDA LEDA 41934
- MCG MCG +03-32-075
- Messier M 91
- NGC NGC 4548
- PGC PGC 41934
- SDSS SDSS J123526.45+142946.8
- UGC UGC 7753
LOOK IT UP ELSEWHERE
] 4 SERVICESEach link carries the identifier printed beside it. Nothing on this page is a measurement of our own, so a number that disagrees with one of these is worth reporting — and a service that has never catalogued this object under this name will say so plainly.
- SIMBADM91
Cross-identifications, measured values and the reference behind each of them.
- NEDM91
Redshift-independent distances, photometry across the spectrum and the extragalactic literature.
- ADSobject:"M91"
Papers indexed against this object rather than against the string, newest first.
- VizieR167″ around 188.8602 +14.4963
Every published table with a row at this position, searched by coordinates rather than by name.
CITE THIS PAGE
] DR1This page is live and its numbers move when an upstream refreshes, so the citation names the release the rows belong to rather than the day you read them. The release itself is frozen, republished as a bundle, and is what a data-availability statement should point at.
SpaceCatalog. M91 [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/m91
@misc{spacecatalog_m91,
author = {{SpaceCatalog}},
title = {{M91}},
howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},
year = {2026},
url = {https://spacecatalog.org/object/m91},
note = {Catalogue entry, data release DR1 (2026-08-21). Values from OpenNGC.}
}The values above were taken from OpenNGC — CC-BY-SA-4.0. Citing this page does not replace citing that catalogue, and its licence is share-alike: the terms reach whatever you build from these rows.