M70 is an eighth magnitude globular cluster in Sagittarius that's faintly visible with binoculars, appearing as a star like point of light. It's much easier to spot with small telescopes where it appears obviously non-stellar but without detail. To resolve M70 into stars, larger scopes are required.
Charles Messier discovered M70 on August 31, 1780, describing it as a "nebula without stars". On the same night he also discovered M69, a neighbouring globular. M70 has an extremely dense core and is believed at some time to have suffered a core collapse, similar to Messier globulars M15, M30 and possibly M62. It was William Herschel who first resolved the cluster into stars, describing it as a miniature version of M3.
M70 is located 29,300 light-years away. Physically it's separated by just 1,800 light-years from M69 with both objects located near to the galactic centre. The clusters are best seen from the Southern Hemisphere during the months of June, July and August. From mid-northern latitudes they are never well positioned and at best climb just a few degrees above the horizon.
Finding M70 is easy once familiar within the teapot asterism of Sagittarius. First locate the two stars that make up the base of the teapot, Kaus Australis (ε Sgr - mag. +1.8) and Ascella (ζ Sgr - mag. +2.6). Imagine a line connecting these two stars. M70 is positioned almost exactly halfway along this line.
At magnitude +8.0, M70 is much easier to spot with larger 11x70 or 20x80 binoculars than with standard 7x50 or 10x50 models. When viewed through 80mm (3.1-inch) scopes, it appears as a faint diffuse ball of light with a slightly brighter central region. Telescopes of the order of 250mm (10-inch) or larger are required to begin resolving some of the outer stars.
In total, M70 covers 8 arc minutes of apparent sky, but visually it appears much smaller than this. The cluster is estimated to be 12.8 billion years old and contains around 75,000 stars.
M70 made headlines in 1995 when Alan Hale and Thomas Bopp observed it and discovered the great comet Hale-Bopp nearby.
M70 Data Table
|Object Type||Globular cluster|
|RA (J2000)||18h 43m 13s|
|DEC (J2000)||-32d 17m 31s|
|Apparent Size (arc mins)||8 x 8|
|Age (years)||12.8 Billion|
|Number of Stars||75,000|
|Notable Feature||Believed to have previously suffered a core collapse|