M105 (mag. +9.8) is an elliptical galaxy located in the constellation Leo that's visible with small telescopes. It was discovered by Pierre Méchain on March 24, 1781, which was three days before he discovered M101. However, due to unknown reasons the galaxy is one of several not included in Charles Messier's final published list. It was eventually added to the list in 1947 by Helen Sawyer Hogg, together with M106 and M107. William Herschel independently rediscovered M105 on March 11, 1784.

M105 is the brightest elliptical member of the Leo I or M96 group of galaxies. This grouping is one of many that lie within the Virgo Supercluster and includes M95, M96 and at least another 21 fainter members. M105 is located 35 Million light-years distant and is known to contain a supermassive black hole at its centre.

Galaxies M95, M96 and M105 are located in the southern section of the middle part of Leo. Imagine a line connecting Regulus (α Leo - mag. +1.4) the brightest star in Leo with Denebola (β Leo - mag. +2.1) the constellations third brightest star. Denebola is positioned about 24 degrees east and a couple of degrees north of Regulus. Located just short of half way along this line are M95, M96 and M105. The northernmost member of the trio is M105 with M96 located 50 arc minutes south of M105 and M95 positioned 40 arc minutes west of M96.

The galaxies are best seen during the months of March, April and May.

M105 Elliptical galaxy by the Hubble Space Telescope (NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M105 (also shown M65, M66, M95 and M96)

Finder Chart for M105 (also shown M65, M66, M95 and M96) - pdf format

Since it's only 10th magnitude in brightness, M105 is a very challenging binocular object. It's easier to spot with large binoculars and when seen through a small 80mm (3.1-inch) scope it appears as a faint diffuse patch of light that's small and round. A larger 200mm (8-inch) scope fairs better with M105 appearing larger and brighter without detail. It has an apparent diameter of about 5 arc minutes but is visually unimpressive when compared with the spirals in Leo. Being an elliptical galaxy, M105 has a high surface brightness, but doesn't show any detail regardless of the size of telescope used.

In the same field of view as M105 - for owners of large scopes - are faint galaxies NGC 3384 and NGC 3389. The three galaxies form a small triangle with NGC 3384 a mag. +10.9 lenticular galaxy and NGC 3389 a mag. +12.4 spiral galaxy, although spotting NGC 3389 requires at least a 250mm (10-inch) scope.

M105 has an actual diameter of 54,000 light-years and is estimated to contain 40 billion stars.

M105 Data Table

Messier105
NGC3379
Object TypeElliptical galaxy
ClassificationE1
ConstellationLeo
Distance (kly)35,000
Apparent Mag.9.8
RA (J2000)10h 47m 50s
DEC (J2000)12d 34m 53s
Apparent Size (arc mins)5.3 x 4.8
Radius (light-years)27,000
Number of Stars40 Billion
Notable FeatureMember of the Leo I or M96 group of galaxies

Sky Highlights - April 2017

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