Globular cluster
M 55 (NGC 6809)
Globular cluster
A globular cluster of hundreds of thousands of old stars orbiting in the Galaxy’s halo: among the oldest objects of the Milky Way, about 12 billion years old. Its metal abundance is 1.1 % of the Sun’s. Distance, brightness and structure come from the Harris catalogue.
| Type | Globular cluster |
|---|---|
| Constellation | Sagittarius |
| Distance | 5,400 pc (17.6 thousand ly) |
| Metallicity [Fe/H] | -1.94 |
| Half-light radius | 4.5 pc |
| Central concentration (c) | 0.93 |
| Radial velocity | 174.7 km/s |
| Source | Harris 1996 (2010) |
| Right ascension (J2000) | 19h 39m 59.7s |
| Declination (J2000) | −30° 57′ 53″ |
In the sky
Visible from the whole Southern Hemisphere and north to latitude 59° N. South of latitude 59° S it never sets. It stands highest at midnight in July, the best time to observe it.
Through a telescope from Earth
Light's journey
The light you see tonight set out 18 thousand years ago. At that time Homo sapiens was spreading out of Africa; there was no farming yet. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 312 million years.