A sky field near some of the brighter galaxies in the Virgo cluster. The most prominent galaxies are circled but inspection of the Larger Version of this picture will show dozens more. The large elliptical galaxy at the centre is the Lenticular Galaxy M84; the elongated image of NGC 4388 (an active spiral galaxy) is in the lower left corner.

The Virgo cluster is a cluster of galaxies, approximately 15 to 22 Mpc distant, comprising approximately 1300 (and possibly up to 2000) member galaxies. The cluster forms the heart of the larger Local supercluster, of which the Local Group is an outlying member. Download high resolution version (750x825, 83 KB)A star field in the Virgo Cluster. ... Download high resolution version (750x825, 83 KB)A star field in the Virgo Cluster. ... The Lenticular Galaxy M84 (also known as Messier Object 84, Messier 84, M84, or NGC 4374) is a lenticular galaxy in the Virgo constellation. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... The megaparsec (abbreviated Mpc) is a unit of distance used in astronomy, equal to one million parsecs. ... The Virgo Supercluster or Local Supercluster is the supercluster of galaxies that contains the Local Group and with it our galaxy, the Milky Way. ... Map of the local group The Local Group is the group of galaxies that includes our galaxy, the Milky Way. ...

The cluster was discovered by Charles Messier in 1781, who charted many of its prominent member galaxies, including the giant M87 galaxy. Charles Messier Charles Messier (1730-06-26 - 1817-04-12) was a French astronomer who in 1774 published a catalogue of 45 deep sky objects such as nebulae and star clusters. ... 1781 was a common year starting on Monday (see link for calendar). ... The jet emitted by M87 in this image is thought to be caused by a supermassive black hole at the galaxys center. ...

The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Many of the member galaxies of the cluster are visible with a small telescope. The distance to the cluster is still an open question, with current best guesses, based on Cepheids using the Hubble Space Telescope, yielding an average of approximately 20 Mpc [1] (http://nedwww.ipac.caltech.edu/level5/Binggeli/Bin4.html). See VIRGO (physics) for a French-Italian project in physics. ... A Cepheid variable is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute stellar luminosity. ... The Hubble Space Telescope (HST) is a telescope orbiting the Earth at the outer edges of the atmosphere. ...

The cluster is a fairly heterogenous mixture of spirals and ellipticals. It is currently believed that the spirals of the cluster are distributed in a cigar-shaped prolate filament, approximately 4 times as long as wide, stretching along the line of sight from the Milky Way and connecting on its back end to the W cloud [2] (http://nedwww.ipac.caltech.edu./cgi-bin/nph-ex_refcode?refcode=1993ApJ...412L..13F). The ellipticals are concentrated much more than the spirals. 2004 is a leap year starting on Thursday of the Gregorian calendar. ... A spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... The W cloud is a cloud cluster of galaxies approximately 25-30 megaparsecs distant. ...

The cluster is an aggregrate of at least three separate subclumps centered on the galaxies M87, M86, and M49. Of the three subclumps, the one centered on M87 is the dominant one, with a mass of approximately 10¹⁴ solar masses, which is approximately an order of magnitude larger than other the other two subclumps [3] (http://nedwww.ipac.caltech.edu/level5/Binggeli/frames.html). A subcluster or subclump (or subgroup) is a term used in galactic astronomy to include a identifiable isolated grouping of galaxies within a cluster of galaxies, typically centered on a large dominant member. ... The jet emitted by M87 in this image is thought to be caused by a supermassive black hole at the galaxys center. ... The Lenticular Galaxy M86 (also known as Messier Object 86, Messier 86, M86, or NGC 4406) is a lenticular galaxy in the Virgo constellation. ... Elliptical Galaxy M49 (also known as Messier Object 49, Messier 49, M49, or NGC 4472) is an elliptical galaxy in the Virgo constellation. ...

The large mass of the cluster is indicated by the high peculiar velocities of many of its galaxies, sometimes as high as 1,600 km/s with respect to the cluster's center. The term peculiar velocity refers to the components of a receding galaxys velocity that cannot be explained by Hubbles law. ... KM, Km, or km may stand for: Khmer language (ISO 639 alpha-2, km) Kilometre/Kilometer (only km in minuscule is the correct representation of kilometer as an SI unit of length) Kinemantra Meditation Knowledge management, in the field of Library and information science Knowledge Machine, the KM knowledge representation... This article is about the unit of time. ...

The Virgo cluster lies within the Local supercluster, and its gravitational effects slow down the nearby galaxies. The large mass of the cluster has the effect of slowing down the recession of the Local Group from the cluster by approximately ten percent. The Virgo Supercluster or Local Supercluster is the supercluster of galaxies that contains the Local Group and with it our galaxy, the Milky Way. ...

More info:

• University of California site (http://cosmology.berkeley.edu/Education/superclusters.html) on Virgo cluster.
• California Institute of Technology site (http://nedwww.ipac.caltech.edu/level5/Binggeli/Bin4.html) on Virgo cluster.
• Heron Island Proceedings (http://msowww.anu.edu.au/~heron/Tonry/tonry_p2.html)
• Chandra X-Ray Observatory: The Virgo Cluster (http://chandra.harvard.edu/xray_sources/virgo/)
• The Virgo Cluster of Galaxies (http://www.seds.org/messier/more/virgo.html), SEDS Messier pages