Messier 30: Globular Cluster in Capricornus

Messier 30 is a small, bright-cored globular cluster in the eastern part of Capricornus. It sits low for northern observers but is easy to locate next to a 5th-magnitude star.

What it is

M30 is a globular cluster, a dense ball of very old stars orbiting in the halo of the Milky Way. It lies about 27,600 light-years away, and its 12′ apparent size corresponds to roughly 95 light-years across. M30 is a core-collapsed cluster: over billions of years, close encounters between stars have made the heavier stars sink toward the middle, so the center has become extremely dense. Such crowded cores are good places for stars to collide or pass close to each other, and Hubble images of M30 show many "blue stragglers," stars that look younger than the rest and probably formed from mergers or mass transfer in close pairs. Another core-collapsed globular in the Messier list is M15 in Pegasus.

When to see it

M30 is an autumn object. From about 40°N it is highest in the south around 10–11 p.m. in late September, and it is best caught in the early evening during September and October. It reaches only about 27° above the horizon at 40°N, so a clear southern horizon helps. From the Southern Hemisphere it rides high and is much easier to see well.

How to find it

Find the triangular pattern of Capricornus, low in the south below Aquila and Aquarius. Near its southern edge is Zeta Capricorni, a 4th-magnitude star. M30 lies about 3.3° east and slightly south of Zeta Capricorni. The 5th-magnitude star 41 Capricorni sits only about half a degree east of the cluster, so when you have that star in a finder, M30 is right beside it. You can also start at Delta Capricorni (Deneb Algedi), the brightest star of the constellation: M30 lies about 7° south and slightly west of it.

What you will see

In binoculars M30 is a small, fuzzy spot next to 41 Capricorni, best from a dark site. A 70–100 mm telescope shows a round glow with a bright, star-like center. A 200 mm or larger telescope at high power resolves the outer parts into faint stars, and some observers see short chains of stars running away from the core. Because it is low in the sky, haze and light pollution affect it strongly; from the suburbs only the core may show. No filter helps.

History

Charles Messier discovered M30 in August 1764 and described it as a round nebula containing no stars. William Herschel resolved it into stars in the 1780s.