Globular star clusters have always been among my favorite deep-sky objects. These wondrous swarms of ancient suns are impressive sights in almost any telescope.

Because globulars are more numerous in the direction of the Milky Way's center, located in Sagittarius, summer nights (in the Northern Hemisphere; winter nights in the Southern) are the best time for globular hunting. In fact, these clusters are so plentiful in this part of the sky that one can view several at once! Let's pay a visit to a few close couples.

The Scorpion's Heart

Our first stop is in Scorpius, where we find the pair of M4 and NGC 6144 separated by almost exactly 1°. The huge, loose cluster M4 is only 1.3° west of brilliant Antares. Despite this star's glare, Walter Scott Houston was able to discern M4 without optical aid while visiting Central America. At a distance of only 7,000 light-years, it is probably the nearest of all globular clusters and therefore one of the easiest to resolve — even a small telescope will show a few of the cluster's individual stars. Look for a string of 11th-magnitude stars forming a striking bar across the center of the cluster. This feature is most prominent in an 8-inch telescope, and in larger instruments it appears enmeshed in a multitude of fainter stars. As with almost any cluster, the longer one stares, the more patterns seem to emerge. While observing with a 17½-inch Dobsonian reflector under the dark skies of the Texas Star Party, I noted many curved lines of stars around M4's margins and a Y-shaped group northeast of the central bar.

Hiding between M4 and Antares is the diminutive 9th-magnitude globular NGC 6144. Clean optics, which minimize scattered light from nearby Antares, help when viewing this globular. Even if you haven't seen it with a telescope, you're probably familiar with pictures of it. NGC 6144 appears in most photographs that show the rich and colorful complex of bright and dark nebulae that begins on the cluster's northern edge and extends northward to the multiple star Rho (ρ) Ophiuchi. My only view of NGC 6144's peppering of 14th-magnitude stars was with a 24-inch Cassegrain reflector in Prince George, British Columbia, at latitude 54° north. As it is always twilight from that latitude when Scorpius culminates, the view I had could probably be easily matched by a 10-inch telescope at a more southerly location.