m5 – globular cluster


Lupe Rioné, Amateur astronomer (Spain)


Globular cluster


The Serpent Constellation


24,500 light years


165 light years

Globular clusters: Globular clusters are concentrations of thousands to millions of stars joined gravitationally. They all orbit in the halo of a galaxy, although some of them can be located near the center of the Milky Way.

Do you want to know more about stellar clusters?

Continuing with the objects of the Messier Catalog, today we talk about the M5 Globular Cluster, also listed as NGC 5904. Although all globular clusters look similar, they differ in size, number, and types of stars they house. In addition to the distance at which they are located. Globular clusters are as old as our own Milky Way, and their study has always been crucial to understanding the formation of galaxies and their evolution.

The globular cluster M5 is probably one of the most interesting because it is one of the oldest, largest, and brightest clusters. It is located in the constellation of The Serpent (Serpens) at a distance of approximately 24,500 light years, and although it has a diameter of 165 light years, its gravitational influence is much greater.

History and Discovery

M5 was discovered in 1702 by the German astronomer Gottfried Kirch and his wife, while they were observing a comet. At first, they thought it was a nebula. The same thing happened to Charles Messier, who observed it in 1764 and included it in his catalog as M5, saying; “I have seen a beautiful nebula in the Constellation of the Serpent… the nebula does not contain any stars… it is round…” It was justified that he was not able to distinguish it as a globular cluster, since his telescope was not large enough to resolve the object in detail.

Who did determine the nature of this object was William Herschel. In 1791, the astronomer counted as many as 200 stars in the cluster, further stating “that the center is so compressed that it is impossible to distinguish the stars in the nucleus”.

M5 globular cluster. Credit: NASA/Hubble/ STScl

M5 cluster. Credit: Adam Block, MT. Lemmon Sky Center, University of Arizona


M5 is the brightest cluster that can be observed from the Northern Hemisphere, almost as bright as the Hercules cluster (M13). Located in the Serpent Constellation, just between the constellations Libra and Boyero, it can be distinguished as a weak object, even in the city. Like the globular cluster M3, we can turn to the star Arthur and jump to Antares to find it. With an apparent magnitude of 5.6, it can be distinguished from a star with binoculars. Already, with a telescope of about 150-200 mm in diameter we can distinguish many individual stars.


M5 is one of the largest known globular clusters, and astronomers estimate that it is one of the oldest, with an age of about 13 billion years. Estimating that it can hold about 500,000 stars, the cluster is located in the halo of our galaxy, at a distance of about 24,000-25,000 light-years; a distance that becomes greater because it moves away from us at a speed of about 52 km/second. With a diameter of about 160 light-years, it is one of the largest known globular clusters, and its gravitational influence is more than 400 light-years. We call gravitational influence the area of space where any object is attracted by the cluster’s gravity, rather than the galaxy’s gravity.

Zoomed M5 image: NASA/ESA

M5 Credit: Velillacanoj@gmail.com. Telescope TS102f5.2 and camera Atik 41ex

It contains a large number of red and blue giant stars in an extremely dense core. There are 105 known variable stars, of which 97 are of the RR Lyrae type. RR Lyrae type stars, also known as “cluster variables,” are somewhat similar to cepheid variables and can be used to measure distances because their relationship between periods and luminosities is well known. The brightest variable of M5 varies from magnitude 10.6 to 12.1 over a 26-day period.

In addition, M5 is known to contain a dwarf nova. This body is not a small supernova. It is a type of variable star formed by a binary system. One of the stars is a white dwarf, accompanied by a giant star that loses matter due to the gravitational pull of the dwarf star. This causes the giant star to undergo abrupt brightness changes, even in a single day. On top of that, M5 contains two pulsars with rotation periods measured in milliseconds. All these characteristics make it an extraordinary object, very attractive to be observed and photographed.

Location of M5. Credit: ESO, IAU and Sky &Telescope

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M10 – Globular Cluster | Cúmulo Globular

M10 is a very bright and star-rich cluster. Located in the constellation Ofiuco, it is estimated to be approximately 16,000 light-years from the center of our galaxy. An analysis of its radial velocity allows us to deduce that it is moving away from Earth at more than 271,440 km/h.

M9 – Globular Cluster | Cúmulo Globular

Like all globular clusters, M9 is a spectacle in itself, and one of the oldest and most intriguing objects in our galaxy. M9 stands out as one of the closest globular clusters to the center of our galaxy, only 5,500 light-years away.

M8 – Lagoon Nebula | Nebulosa de la Laguna

Like all emission nebulae, M8 or NGC 6523 is a gigantic HII region, that is, a spectacular cradle of stars. With a magnitude of 5.8, this incredible nebula boasts many large, hot stars, whose ultraviolet radiation sculpts the gases and cosmic dust, giving it its characteristic shape.

M7 – Open Cluster | Cúmulo Abierto

Also known as NGC 6475, M7 is an open cluster, that is, a group of gravitationally bound stars formed by the same molecular cloud. It is a very sparse cluster, located in a very rich region of the Milky Way.

M6 – Open Cluster | Cúmulo Abierto

This beautiful cluster comprises more than 200 stars and has a diameter of about 12-20 light-years. It is estimated that its stars were formed about 100 million years ago, which means that while dinosaurs roamed the planet, M6 was just beginning to shine in the sky.

M5 – Globular Cluster | Cúmulo Globular

The globular cluster M5 is probably one of the most interesting because it is one of the oldest, largest, and brightest clusters. It is located in the constellation of The Serpent (Serpens) at a distance of approximately 24,500 light-years.

M4 – Globular Cluster | Cúmulo Globular

Also called NGC 6121, M4 is the closest globular cluster to the Earth. M4 contains about 100,000 stars, and like most globular clusters, it is a very old structure, about 12-13 billion years old.

M3 – Globular Cluster | Cúmulo Globular

M3, also called NGC 5272, is one of the largest and most spectacular clusters that we can observe in our galaxy. In fact, M3 was the first original discovery by Charles Messier.

M2 – Globular Cluster | Cúmulo Globular

M2 is a globular star cluster and the second object in the Messier catalog. Also called NGC 7089, it was discovered in 1746 by French astronomer Jean-Dominique Maraldi.

M1 – Crab Nebula | Nebulosa del Cangrejo

M1 is the remnant of a supernova explosion that was observed by Chinese astronomers during the Song Dynasty in the 11th century.


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