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Messier 70

Globular Cluster M70 (NGC 6681), class V, in Sagittarius

[m70.jpg]
Right Ascension 18 : 43.2 (h:m)
Declination -32 : 18 (deg:m)
Distance 30.5 (kly)
Visual Brightness 7.9 (mag)
Apparent Dimension 8.0 (arc min)

Discovered 1780 by Charles Messier.

Messier 70 (M70, NGC 6681) is one of the less bright and conspicuous globular clusters in Messier's catalog.

Appearing roughly as bright and big as its neighbor M69, globular star cluster M70 is indeed only a little more luminous and little bigger, and almost at the same distance (M70: 30,500 light years, M69: 29,000 light years). With their close angular proximity and similar distance, they are also physically close together, with a physical distance of about 1,970 ly from each other. Both are quite close to the galactic center, so they are both subject to quite strong tidal gravitational forces. As it is also at about the same southern declination, it is a difficult object from Paris where Messier observed it.

Charles Messier discovered this globular on August 31, 1780, and described it as a "nebula without star." William Herschel was the first to resolve this globular cluster into stars and describes it as "a miniature of M3."

M70 is 8.0 arc minutes in apparent angular and roughly 68 light years in linear diameter, its bright visual core being only about 4'. It is rapidly receding from us, at about 200 km/sec. Only 2 variables are known in this stellar swarm.

The core of M70 is of extreme density, as it has undergone a core collapse somewhen in its history, similar to at least 21 and perhaps up to 29 of the 150 known Milky Way globulars, including M15, M30, and possibly M62 and M79.

Holger Baumgardt et.al. (2023) investigated astrometrical data from the GAIA satellite, and from the position and velocity, derived M70's simulated orbit. They found that M70 is at a distance of 30.5 kly (9.36 kpc) from us and 7.5 kly (2.29 kpc) from Galactic Center, so slightly behind the Galactic Center from us. Its orbit lets it come in as close as 2.6 kly (0.81 kpc) from Galactic Center, and takes it out again to 19.5 kly (4.98 kpc), with a period of about 60 Myr. It has passed its perigalacticum lesss than 5 Myr ago, and its apogalacticum almost 40 Myr in the past. From fitting of its Color-Magnitude Diagram (CMD), the authors also found an age of 12.7 Gyr for M70. From the velocity dispersion of its member stars, they determined its mass as 105,000 solar masses, and a half-mass radius of 9.9 light years (3.04 pc).

According to Clement (2025), M70 contains only 6 variable stars, 5 discovered in 1962 by Rosino, the 6th in 1983 by Liller. All are RR Lyrae variables, 1 of subtype RR0, 4 RR1, and 1 of undetermined subtype. According to Freire (2025), M70 hosts a total of 6 pulsars, 1 of them binary, 4 isolated, and 1 to be determined. They were discovered only in 2024 (3) and 2025 (the other 3).

Globular cluster M70 became famous in 1995 when the great comet Hale-Bopp was discovered near it by Alan Hale and Thomas Bopp as they were observing this globular.

  • Historical Observations and Descriptions of M70
  • More images of M70
  • Amateur images of M70

  • Marco Castellani's data for M 70
  • Christine Clement's Catalog of Variable Stars in M70
  • Pulsars in globular cluster M70 (Paolo Freire)
  • Holger Baumgardt's Fundamental Data for M70 (NGC 6681)
  • SIMBAD Data of M70
  • NED Data of M70
  • Publications on M70 (NASA ADS)
  • Observing Reports for M70 (IAAC Netastrocatalog)
  • NGC Online data for M70

  • Wikipedia page for Messier 70
  • Messier 70 in Hubble's Messier Catalog

    References


    Hartmut Frommert
    Christine Kronberg
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    Last Modification: January 11, 2026
    Former definitive version: August 30, 2007