NGC 5694, also known as Caldwell 66, is a faint globular cluster in the constellation Hydra. At mag. +10.2, it's not a bright object and the reason is simply due to its distant. At approx. 114,000 light-years, it's further away than the actual diameter of the Milky Way galaxy. However, despite this it can be spotted with amateur telescopes, although virtually impossible to resolve in most backyard instruments.
William Herschel discovered NGC 5694 on May 22, 1784. Even when using the best telescope of the day, Herschel couldn't resolve it into stars and catalogued it as a faint nebula. The object was first resolved and at the same time its true nature determined by Carl Lampland and Clyde Tombaugh in 1932. Recent measurements suggest that it's moving fast enough to eventually escape the galaxy and move into intergalactic space.
The cluster is best seen from southern and equatorial latitudes during the months of April, May and June.
NGC 5694 is located in the far eastern part of Hydra, close to the Libra border. Antares, mag. +1.0, the brightest star in Scorpius is positioned 24 degrees east of the globular. NGC 5694 can be spotted with small scopes. A 100mm (4-inch) refractor at 200x magnification reveals a small fuzz, spanning 3.6 arc minutes, that's clearly non-stellar. Through a 250mm (10-inch) reflector, NGC 5694 appears round with a gradual brightening towards the centre. It's not resolvable as the brightest member stars shine at mag. +15.5. A very large 500mm (20-inch) scope will partially resolve the cluster, especially on nights of good seeing and transparency.
NGC 5694 has a spatial diameter of 120 light-years and is estimated to contain 250,000 stars. It's one of a handful of globulars more than 100,000 light-years distant that can be seen with amateur scopes.
NGC 5694 Data Table
|Object Type||Globular Cluster|
|RA (J2000)||14h 39m 36s|
|DEC (J2000)||-26d 32m 18s|
|Apparent Size (arc mins)||3.6|
|Number of Stars||250,000|
|Notable Feature||One of the more remote globular clusters of the Milky Way|