Messier 108 — Galaxy in Ursa Major

M108 (NGC 3556) is an edge-on spiral galaxy in the constellation Ursa Major, located approximately 45.9 million light-years from Earth. The galaxy spans about 90,000 light-years across and is seen nearly edge-on, tilted about 75 degrees to our line of sight. This orientation reveals a chaotic, mottled disk structure with prominent dust lanes, bright knots of star formation, and numerous HII regions scattered along its length. Unlike many edge-on galaxies, M108 shows no prominent central bulge, giving it a somewhat ragged, irregular appearance. The galaxy is a member of the Ursa Major Cluster of galaxies, a loose association of galaxies spanning a large area of the sky. M108 lies in a spectacular location in the sky, just 48 arcminutes southeast of the famous Owl Nebula (M97), making the pair a popular target for astrophotographers who can capture both objects in a single wide-field frame.

Located about 1.5 degrees southeast of Merak (Beta Ursae Majoris), the southwestern pointer star of the Big Dipper, and less than a degree from M97 (the Owl Nebula). At magnitude 10.0, M108 requires a telescope to observe. A 4-inch telescope at 80-100x shows an elongated streak of light oriented roughly northwest-southeast. An 8-inch telescope at 150x reveals the mottled, uneven surface brightness with dark patches from dust lanes. Larger telescopes (12 inches and up) at moderate magnification begin to show knots of star formation and the galaxy's irregular, clumpy texture. Try observing M108 and the Owl Nebula in the same low-power field — they make a stunning contrasting pair, a galaxy and a planetary nebula side by side. Best observed from February through June.

Discovered by Pierre Mechain on February 19, 1781, three days after he discovered M97, the Owl Nebula nearby. Like several other Mechain discoveries, M108 was not included in the original Messier catalog but was added by Owen Gingerich in 1953 based on Mechain's descriptions and positional notes. The galaxy's edge-on orientation and rich dust structure have made it a frequent subject of studies on interstellar medium properties in spiral galaxies. Multiple supernovae have been recorded in M108, including SN 1969B.