M36, M37 and M38 form a triplet of star clusters in a row in the constellation Auriga. They make a superb set of binocular targets. In a telescope that is large enough, they can be bright and beautiful.
Although the clusters are similar in size and appearance, a closer look shows that each is unique.
M36 is the smallest of the three in our sky at just 1/3 the size of the moon. It has the fewest stars. Because it appears to have arcs of stars coming out from its center, it is also called the Pinwheel Cluster.
M37 (shown above) is the second largest, about 1/2 the size of the moon. It is the brightest of the three with a rich concentration of central stars.
M38 is the largest of the three, about 2/3 the size of the moon. Because it appears to have many of its stars in numerous arms reaching out from a round center, it is also called the Starfish Cluster.
Viewing M36-M37-M38 Clusters
Mid-December to late March
Find Capella in Auriga. Then find the two lower stars, Theta Aurigae and Elnath. Use these two stars to form a upwards-pointing triangle to find M36. Repeat this to form a downwards pointing triangle to find M37. Look above M36 to find M38. M36 and M37 are about 4° apart. M36 and M38 are about 2.5° apart.
All three clusters are easily visible in binoculars from a dark site.
After finding each in binoculars, view it with a telescope. With a large enough telescope, the size, concentration and shape of the cluster will be easily revealed. Try drawing what you see.