- M 108 (NGC 3556)
M 108 (NGC 3556) is located in the constellation Ursa Major. It is a spiral galaxy that we view almost edge-on. The galaxy has extensive dark dust clouds along its major axis which largely obscure the outer edges of the galaxy on either side of the bulging central region. A few pinkish HII regions can be seen along the dark lanes near the visual center of the galaxy. M 108 is thought to be a member of the Ursa Major Group that lies at around 45 million LY from us. The galaxy has a diameter of around 100,000 LY. It was discovered by Pierre Mechain (Messier's colleague) in February of 1781, but was not included in Messier's original publication. It was included as a Messier object only in 1953, when several objects mentioned in Messier's or Mechain's notes or correspondence were added to the overall list. Three foreground stars can be seen lying on top of the galaxy. The brightest of the three near the visual center of the galaxy is often mistaken for the core of the galaxy. The actual core of the galaxy can't be seen in visible wavelengths due to the dust clouds. These stars have also been mistaken for supernovas in the galaxy. If you look carefully, you'll see that the brightest of the three stars has a small companion (just to its right). This companion has been called Brenner's Star and is used as a test of a telescope's resolution. To visually detect this companion star, you typically need a scope with at least a 20-inch mirror and a magnification of over 300X.
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