Messier 79: Globular Cluster in Lepus

Messier 79 is the winter sky's only Messier globular cluster. It sits in Lepus, the hare at Orion's feet, in the part of the sky that faces away from the center of our galaxy, where globular clusters are rare.

What it is

M79 is a globular cluster about 42,700 light-years from us. Its 9.6-arcminute glow corresponds to roughly 120 light-years across. Most globulars crowd around the galactic center, but M79 is on the opposite side of the sky, about 60,000 light-years from the center. SEDS reports an age of about 11.7 billion years and a mass of about 180,000 Suns from a 2023 Gaia-based study, and notes that its orbit is extremely elongated, swinging from far outside the galaxy to very close to the center. Its unusual position and orbit have led astronomers to suggest that the Milky Way took it from another galaxy, most likely the Canis Major Dwarf Galaxy, which our galaxy is slowly absorbing.

When to see it

M79 is a winter object. It crosses the meridian around midnight in mid-December and around 9 p.m. in late January. From 40°N it rises only to about 25° above the southern horizon, so you need a clear, low southern view. It is much better from the Southern Hemisphere, where it passes high overhead on summer evenings.

How to find it

Start at Rigel, Orion's bright blue-white foot. About 10° south-southeast you will find the two brightest stars of Lepus: Arneb (Alpha Leporis) and, about 3° south of it, Nihal (Beta Leporis). Draw a line from Arneb through Nihal and continue it the same distance and a bit more, about 4° beyond Nihal. M79 sits there; sweep slowly with a low-power eyepiece and look for a small fuzzy spot that does not focus to a point.

What you will see

In binoculars M79 is a small, round, slightly fuzzy spot that is easy to mistake for a star at first. A 70–100 mm telescope shows a bright, compact glow with a dense center, and at higher power its edges start to look grainy. In a 200 mm telescope the outer parts resolve into many faint stars around a bright, tightly packed core. Because it stays low from northern latitudes, haze and light pollution near the horizon dim it; observe it when it is due south.

History

Pierre Méchain discovered M79 on October 26, 1780, and told Charles Messier, who added it to his catalog on December 17, 1780. William Herschel first resolved it into stars and recognized it as a globular cluster around 1784. In 2024 astronomers found its first known pulsar.