Messier 80: Globular Cluster in Scorpius

Messier 80 is a small, bright, tightly packed globular cluster in the head of Scorpius. It sits in the same patch of sky as M4, and the two make a fine contrast: M4 loose and sprawling, M80 small and concentrated.

What it is

M80 is a globular cluster about 33,700 light-years away, holding several hundred thousand stars. Its 10-arcminute glow corresponds to roughly 100 light-years across. It is one of the densest globular clusters in the Milky Way. In 1999 the Hubble Space Telescope found that its core holds a large number of "blue stragglers," stars that look younger and hotter than the rest of the cluster. They are thought to form when stars collide or merge, and their abundance in M80 points to a high rate of close encounters in its crowded center.

In May 1860 a nova, now called T Scorpii, flared up in M80. It reached about magnitude 7, outshining the whole cluster for a few days, then faded within weeks.

When to see it

M80 is best on late spring and early summer evenings. It crosses the meridian around midnight in late May and around 10 p.m. in late June. From 40°N it reaches about 27° above the southern horizon, so a clear southern view helps. From the Southern Hemisphere it passes nearly overhead on winter evenings.

How to find it

Start at Antares, the bright orange heart of Scorpius. Then find Acrab (Beta Scorpii), the northern star of the line of three that forms the scorpion's head, about 8½° to the northwest of Antares. M80 sits almost exactly halfway between the two stars, about 4½° from Antares. Aim your finder at the midpoint and look for a small, fuzzy star.

What you will see

In binoculars M80 is a small, bright, round spot that looks like an out-of-focus star or a tailless comet, as Messier described it. A 70–100 mm telescope shows a compact glow, bright in the middle and fading toward the edges, about 3 to 5 arcminutes across, with little or no resolution. In a 200 mm telescope at high power the outer edges begin to break into faint stars, but the core stays a blazing, unresolved center. Its brightness lets it stand up to suburban skies, though its low altitude from northern latitudes works against you.

History

Charles Messier discovered M80 on January 4, 1781, describing a nebula without a star that looked like the nucleus of a comet. William Herschel resolved it into stars before 1785 and called it one of the richest and most compressed clusters he had seen. The 1860 nova was discovered by Arthur Auwers in Berlin and independently seen by Norman Pogson.