Deep-Sky Objects: Messier 80

Deep-Sky Objects: Messier 80

M80 is a massive globular cluster located about 32,600 light years away in the constellation Scorpius, and as globular clusters go, it has been described as being the northern hemispheres’ equivalent of Omega Centauri (NGC 5139), the biggest and most massive globular star cluster associated with the Milky Way galaxy. After Omega Centauri, M80 is one of the most densely packed Milky Way globulars, containing about 200,000 stars.

Quick Facts

• Constellation: Scorpius
• Coordinates: RA: 16h 17m 02.41s|Dec. -22°58’33.9”
• Distance: 32,600 light years
• Cluster Type: Globular
• Mass: 400,000 sol
• Radius: 48 light years
• Apparent Magnitude: +7.87
• Age: 12.54 billion years
• Best seen: Summer
• Other Designations: Messier 80, NGC 6093, GCl 39, C 1614-228, MWSC 2376


M80 is located within Scorpius, a beautiful zodiac constellation situated between Libra to its east, and Sagittarius to its west. While M80 is visible from between +40° and -90° of latitude, it is not always easy to find without the use of an optical aid, such as a small telescope. Look for this globular cluster about four degrees northwest of the star Antares (Alpha Scorpii), and about halfway towards the star Akrab (Beta Scorpii) in the same region of the sky that also contains M4, another conspicuous cluster in Scorpius. The best time to view M80 is during summer, when Scorpius is relatively high above the horizon.

Physical Properties

Globular star clusters are thought to be remains of the “building blocks” out of which galaxies formed, and in the case of M80, much of these remains have, well, remained. Seen from Earth, M80 has an angular diameter of 10 minutes of arc, which corresponds to an actual diameter of 96 light years at its distance from Earth.

While the cluster is an easy target for small telescopes as a fuzzy ball of light, instruments of 8-inch and larger apertures show the clusters’ bright core and extended halo as distinctly different parts of the cluster, and 12-inch and larger instruments will be able to resolve several dozen of the brightest stars in the cluster individually. Even though all globular star clusters are spectacular sights in a telescope, Admiral William Henry Smyth provided perhaps the best description of M80 when he observed it in April of 1837. Here is a part of his description:

“This is a very important object when nebulae are considered in their relations to the surrounding spaces, which spaces, Sir William Herschel found, generally contain very few stars: so much so, that whenever it happened, after a short lapse of time, that no star came into the field of his instrument, he was accustomed to his assistant, “Make ready to write, Nebulae are just approaching.” Now our present object is located on the western edge of a vast obscure opening, or space of 4 deg in breadth, in which no stars are to be seen; and Sir William pronounced 80 Messier, albeit it had been registered as nébuleuse sans étoiles [nebula without stars], to be the richest and most condensed mass of stars which the firmament can offer to the contemplation of astronomers.”


As is the case with most globular clusters, M80 contains a relatively high number of “blue stragglers”, which are stars that appear to be much younger, hotter, and massive compared to the average, temperature, mass, and age of the majority of stars in the cluster. Given that the cluster’s estimated age is more than 12 billion years, all the stars are expected to be ancient, which is what makes its apparently hot, young stars more conspicuous. Essentially, blue stragglers are stars that have either collected material from other, nearby stars, or have gained mass in direct mergers between stars. In fact, Hubble images show large areas within the cluster where blue stragglers exist in very high densities, which suggests that the inner regions of M80 is so dense that stars are actively engaged in stripping material from each other, or are colliding frequently.

One other possible mechanism that can trigger the formation of blue stragglers is the explosion of a star in a dense region of the cluster. One such event was observed on May 21st, 1860, when a variable star of the T Scorpii-class brightened from magnitude +70 to an absolute magnitude of -8.5, which is about 200,000 times more luminous than the Sun, outshining the entire cluster for a few days.

M80 also contains a relatively high number of rapidly spinning neutron stars, emitting tightly focused beams of electromagnetic radiation that can be detected when such a beam sweeps over Earth. In addition, the cluster contains a high number of radio pulsars; in fact, the radiation emitted by around 3,000 stars in M80 have been modified to make it audible to human hearing. So, if you have ever wondered what a huge globular star cluster sounds like, you can find out here:

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