Messier 109: Barred Spiral Galaxy in Ursa Major

M109 is a barred spiral galaxy that sits less than a degree from Phecda, the star at the southeast corner of the Big Dipper's bowl. It is easy to find but not so easy to see well, because Phecda's glare sits just outside the field and the galaxy itself is a modest, faint oval.

What it is

M109 is a barred spiral: a straight bar of stars runs through its center, and the spiral arms start from the ends of the bar, much as in our own Milky Way. It lies about 60 million light-years away, and its 7′ length works out to roughly 120,000 light-years. It is the brightest member of a group of galaxies in Ursa Major, sometimes called the M109 group, with several dozen smaller companions. In 1956 a supernova, SN 1956A, was seen in it. Two other Messier objects lie below the bowl not far away, the edge-on M108 and the Owl Nebula M97.

When to see it

M109 is a spring object, highest around midnight in late March and high in the evening sky through April and May. From about 40°N it climbs to roughly 77° and never sets, although on autumn evenings it is low in the north. From the Southern Hemisphere it barely clears the northern horizon from around 30°S and is not visible farther south.

How to find it

This is one of the easiest Messier objects to point at. Find Phecda (Gamma Ursae Majoris), the bowl star nearest the handle on the bottom side. M109 lies only about 0.6° southeast of Phecda. Put Phecda just outside the eyepiece field to the northwest, or at the edge of a low-power field, and look for a small oval glow.

What you will see

Binoculars generally will not show M109, and the glare of Phecda makes it harder still. A 70–100 mm telescope under a dark sky shows a small, faint oval with a brighter center; from suburban skies it is often lost. A 200 mm or larger telescope shows an oval glow with a distinct bright core and, with averted vision on a good night, the bar as a slight brightening across the middle. The spiral arms are very faint and need a large telescope and dark sky to suspect. Filters do not help.

History

Pierre Méchain discovered M109 in March 1781, and Messier recorded its position soon after, on March 24, but it was not numbered in the published catalog. In 1953 Owen Gingerich added it to the list as M109, along with M108, using Messier's notes. These 20th-century additions from Messier's and Méchain's records, ending with M110 in 1966, completed the list of 110.