Messier 71
Encyclopedia
Messier 71 is a globular cluster
in the constellation
Sagitta
. It was discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier
in his catalog of comet
-like objects in 1780. It was also noted by Koehler
at Dresden
around 1775.
M71 is at a distance of about 12,000 light years away from Earth
and spans some 27 light years across. The irregular variable star
Z Sagittae is a member of this cluster.
M71 was long thought (until the 1970s) to be a densely packed open cluster
and was classified as such by leading astronomer
s in the field of star cluster research due to its lacking a dense central compression, and its stars having more "metals
" than is usual for an ancient globular cluster; furthermore, it's lacking the RR Lyrae
"cluster" variable stars that are common in most globulars. However, modern photometric photometry
has detected a short "horizontal branch
" in the H-R diagram of M71, which is characteristic of a globular cluster. The shortness of the branch explains the lacking of the RR Lyrae variables and is due to the globular's relatively young age of 9-10 billion years. The relative youth of this globular also explains the abundance of "metals" in its stars. Hence today, M71 is designated as a very loosely concentrated globular cluster, much like M68
in Hydra
. M71 has a luminosity of around 13,200 suns.
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Sagitta
Sagitta
Sagitta is a constellation. Its name is Latin for "arrow", and it should not be confused with the larger constellation Sagittarius, the archer. Although ancient, it is insignificant, for it has no star brighter than the 4th magnitude and is the third smallest of all constellations...
. It was discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
in his catalog of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
-like objects in 1780. It was also noted by Koehler
Johann Gottfried Koehler
Johann Gottfried Koehler was a German astronomer who discovered a number of nebulae, star clusters, and galaxies....
at Dresden
Dresden
Dresden is the capital city of the Free State of Saxony in Germany. It is situated in a valley on the River Elbe, near the Czech border. The Dresden conurbation is part of the Saxon Triangle metropolitan area....
around 1775.
M71 is at a distance of about 12,000 light years away from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
and spans some 27 light years across. The irregular variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
Z Sagittae is a member of this cluster.
M71 was long thought (until the 1970s) to be a densely packed open cluster
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
and was classified as such by leading astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
s in the field of star cluster research due to its lacking a dense central compression, and its stars having more "metals
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
" than is usual for an ancient globular cluster; furthermore, it's lacking the RR Lyrae
RR Lyrae variable
RR Lyrae variables are periodic variable stars, commonly found in globular clusters, and often used as standard candles to measure galactic distances.This type of variable is named after the prototype, the variable star RR Lyrae in the constellation Lyra....
"cluster" variable stars that are common in most globulars. However, modern photometric photometry
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...
has detected a short "horizontal branch
Horizontal branch
The horizontal branch is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's...
" in the H-R diagram of M71, which is characteristic of a globular cluster. The shortness of the branch explains the lacking of the RR Lyrae variables and is due to the globular's relatively young age of 9-10 billion years. The relative youth of this globular also explains the abundance of "metals" in its stars. Hence today, M71 is designated as a very loosely concentrated globular cluster, much like M68
Messier 68
Messier 68 is a globular cluster in the Hydra constellation. It was discovered by Charles Messier in 1780. M68 is at a distance of about 33,000 light-years away from Earth.-External links:* *...
in Hydra
Hydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
. M71 has a luminosity of around 13,200 suns.
External links
- Messier71 @ SEDS Messier pages
- Messier 71, Galactic Globular Clusters Database page
- Messier 71, LRGB CCD image based on two hours total exposure
- Messier 71: an Unusual Globular Cluster, ESA\HubbleHubble Space TelescopeThe Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
picture of the week.