M70 is an eighth magnitude globular cluster located in Sagittarius that's faintly visible with binoculars, appearing "star" like. It's much easier to spot with small telescopes where despite being small with little detail visible, it appear obviously non-stellar. To resolve M70 into stars large amateur scopes are required.
Charles Messier discovered M70 on August 31, 1780, describing it as a "nebula without star". On the same night he also discovered M69, another close by globular (both apparently and spatially). M70 has an extremely dense core and is believed at some time previously to have suffered a core collapse, similar to Messier globulars M15, M30 and possibly M62. It was William Herschel who first resolved M70 into stars, describing it as a miniature version of M3.
M70 is located 29,300 light years from Earth. Spatially, it's separated by only 1,800 light-years from M69 with both objects located close to the galactic centre. They are best seen from the Southern Hemisphere during the months of June, July and August. However, from northern temperate latitudes they are never well positioned, at best climbing just a few degrees above the southern horizon.
Finding M70 is easy once familiar within the teapot asterism of Sagittarius. 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 size models. When viewed through 80mm (3.1-inch) scopes, the globular appears as a faint diffuse ball of light with a slightly brighter central region. Telescope apertures of 250mm (10-inch) or larger are required to start resolving some of the outer stars. In total, M70 covers 8 arc minutes of apparent sky but through amateur scopes, visually it appears much smaller than this. The cluster is estimated to be 12.8 billion years old and contains 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|
|Number of Stars||75,000|
|Notable Feature||Believed to have previously suffered a core collapse|