Messier 108: Edge-On Spiral Galaxy in Ursa Major

M108 is a slim, nearly edge-on galaxy just below the bowl of the Big Dipper, and it shares the neighborhood with the Owl Nebula, M97, less than a degree away.

What it is

M108 is a barred spiral galaxy seen almost exactly edge-on, so its disk appears as a thin, mottled streak. It lies about 46 million light-years away, and its 8′ length works out to roughly 110,000 light-years, about the size of the Milky Way. Its disk is full of dust and patchy star-forming regions, which give it a blotchy look in photographs rather than a neat dark lane. It is part of the loose Ursa Major group of galaxies. Its neighbor in the sky, the Owl Nebula M97, lies only about 2,660 light-years away and has nothing to do with it physically. The barred spiral M109 is nearby under the bowl as well.

When to see it

M108 is a spring object, highest around midnight in early March and high in the evening sky through April and May. From about 40°N it climbs to roughly 74° and never sets, though it is low in the north on autumn evenings. From the Southern Hemisphere it barely clears the northern horizon from around 30°S and cannot be seen farther south.

How to find it

Start at Merak, the bottom star of the Big Dipper's bowl on the side away from the handle. M108 lies about 1.5° southeast of Merak, roughly on the line toward Phecda, the other bottom corner of the bowl. Continue another 0.8° southeast and you reach the Owl Nebula. A wide-field eyepiece can show both at once.

What you will see

Binoculars rarely show M108; very large binoculars under a dark sky might catch a faint dash. A 70–100 mm telescope shows a dim, thin streak of light, oriented roughly east to west, with little sign of a central bulge; suburban skies make it very difficult. A 200 mm or larger telescope under a dark sky shows a long, narrow glow with a patchy, mottled texture and a few knots and darker gaps along its length, plus a faint foreground star superimposed near the middle. Filters do not help with the galaxy, although an O-III filter will improve the nearby Owl.

History

Pierre Méchain discovered M108 in February 1781, and Messier observed it the following month. It was not given a number in the published catalog. In 1953 the American astronomer Owen Gingerich added it to the list as M108, based on Messier's own notes, one of the 20th-century additions from Messier's and Méchain's records.