M108 is a nice edge on barred spiral galaxy located in Ursa Major that was discovered by Pierre Méchain on February 19, 1781. It's not one of the objects included by Messier in his final published catalogue version but was added much later by Owen Gingerich in 1953. This was based on analysis of notes written by Messier and Méchain that referenced M108 suggesting that the object was intended for inclusion in a later version. William Herschel independently rediscovered M108 on April 17, 1789.

Locating M108 is easy since it's positioned only 1.5 degrees southeast of bright Merak (β UMa - mag. +2.3) the southwest corner star of the bowl of the famous Plough or Big Dipper asterism of Ursa Major. Located 50 arc minutes southeast of M108 is the planetary nebula "Owl Nebula" (M97) and both items fit easily in the same wide field telescope field of view.

M108 is best seen from Northern Hemisphere latitudes during the months of March, April and May. For observes located at latitudes greater than 35N, the galaxy is circumpolar and therefore never sets.

M108 Spiral galaxy by the Hubble Space Telescope (NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M108 (also shown M40, M51, M97, M101, M106 and M109)

Finder Chart for M108 (also shown M40, M51, M97, M101, M106 and M109) - pdf format

Finder Chart for M81 (also shown M40, M97, M82, M108 and M109)

Finder Chart for M81 (also shown M40, M97, M82, M108 and M109) - pdf format

M108 shines at apparent magnitude +10.2 and since it's aligned almost face-on the galaxy exhibits a high surface brightness. Therefore, it can be spotted with a small 80mm (3.1-inch) telescope; appearing as a faint strongly elongated streak of light with a slightly brighter central region. A larger 200mm (8-inch) scope reveals a well-defined thin needle structure that displays a mottled dusty complexion with subtle variations in brightness. M108 is a galaxy that can withstand high magnifications and is somewhat similar in appearance to the brighter galaxy M82.

In total, M108 spans 8.6 x 2.4 arc minutes of apparent sky and is located 45 million light-years from Earth. This corresponds to an actual diameter of 110,000 light-years. It's estimated to contain 400 billion stars and the galaxy is believed to be an isolated member of the Ursa Major Cluster of galaxies.

A type II supernova (1969B) was observed in M108 on January 23, 1969, peaking at magnitude +13.9.

M108 Data Table

Messier108
NGC3556
Object TypeBarred Spiral galaxy
ClassificationSB(s)cd
ConstellationUrsa Major
Distance (kly)45000
Apparent Mag.10.2
RA (J2000)11h 11m 31s
DEC (J2000)55d 40m 24s
Apparent Size (arc mins)8.6 x 2.4
Radius (light-years)55,000
Number of Stars400 Billion

Sky Highlights - March 2017

Comet
Comet 41P/Tuttle-Giacobini-Kresak now visible with binoculars as it heads towards perihelion

Mercury
Mercury heading towards greatest elongation east

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for March 2017

Northern Hemisphere
Evening
West:- Venus (mag. -4.8 to -4.1 - first half of month), Mars (mag. +1.3 to +1.5), Uranus (mag. +5.9), Mercury (mag. -1.5 to -0.4 - second half of month)
Midnight
Southeast:- Jupiter (mag. -2.3 to -2.5)
Morning
Southwest:- Jupiter
Southeast:- Saturn (mag. +0.5)

Southern Hemisphere
Evening
West:- Venus (first half of month), Mars, Uranus
Midnight
North:- Jupiter
East:- Saturn
Morning
West:- Jupiter
Northeast:- Saturn
East:- Neptune (mag. +8.0 - second half of month)

Deep Sky
Naked eye / binoculars:-
Melotte 111 - Mel 111 - The Coma Star Cluster (Open Cluster)
Messier 44 - M44 - The Praesepe (Open Cluster)

Telescopes:-
Messier 67 - M67 - Open Cluster
Messier 51 - M51 - The Whirlpool Galaxy (Spiral Galaxy)
Messier 97 - M97 - The Owl Nebula (Planetary Nebula)
Messier 101 - M101 - The Pinwheel Galaxy (Spiral Galaxy)
Messier 65 – M65 – Spiral Galaxy
Messier 66 - M66 - Intermediate Spiral Galaxy
Messier 95 - M95 - Barred Spiral Galaxy
Messier 96 - M96 - Intermediate Spiral Galaxy
NGC 4244 - Spiral Galaxy
NGC 4565 - Needle Galaxy - Spiral Galaxy

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