Messier 2: Globular Cluster in Aquarius

Messier 2 is one of the finest globular clusters of the autumn sky, and it sits in a part of Aquarius that has few other bright objects. It is easy to find and shows up well in binoculars.

What it is

M2 is a globular cluster: a tight ball of very old stars held together by its own gravity, orbiting in the halo of the Milky Way. It holds about 150,000 stars, and NASA gives its age as roughly 13 billion years, so its stars formed when the galaxy was young. At a distance of about 38,100 light-years, its 16′ apparent size works out to roughly 175 light-years across, which makes it one of the larger globulars in the Messier list. It is more than twice as far away as the summer globulars M10 and M12, yet it looks just as bright.

When to see it

M2 is an autumn object. From about 40°N it is highest in the south around 10–11 p.m. in late September, and it stays well placed in the early evening through October and November. Because it lies almost on the celestial equator, it climbs to about 49° above the horizon at 40°N. It is just as easy from the Southern Hemisphere, where it appears in the northern sky in the spring months.

How to find it

Start at Beta Aquarii (Sadalsuud), the brightest star in Aquarius, at magnitude 2.9. M2 lies about 5° almost due north of it, slightly to the east. If you know Enif (Epsilon Pegasi), the bright star marking the nose of Pegasus, M2 sits about a third of the way along a line from Beta Aquarii to Enif. Sweep north from Beta Aquarii with binoculars and the cluster appears as a small fuzzy "star" that refuses to come to focus.

What you will see

In binoculars M2 looks like an out-of-focus star with a bright center, easy even from the suburbs. A 70–100 mm telescope shows a round glow with a brighter core and a grainy texture at the edges at about 100×. A 200 mm or larger telescope under dark skies resolves the outer parts into many faint stars, while the dense center stays a blazing haze. From suburban skies the core is still bright, but fewer outer stars show. No filter helps with star clusters.

History

The French astronomer Jean-Dominique Maraldi found M2 in 1746 while observing a comet. Charles Messier came across it on his own in 1760 and described it as a round nebula containing no stars. William Herschel was the first to resolve it into individual stars, in the 1780s.