Globular cluster
NGC 6638
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 11 % of the Sun’s. Distance, brightness and structure come from the Harris catalogue.
| Type | Globular cluster |
|---|---|
| Constellation | Sagittarius |
| Distance | 9,400 pc (30.7 thousand ly) |
| Metallicity [Fe/H] | -0.95 |
| Half-light radius | 1.4 pc |
| Central concentration (c) | 1.33 |
| Radial velocity | 18.1 km/s |
| Source | Harris 1996 (2010) |
| Right ascension (J2000) | 18h 30m 56.1s |
| Declination (J2000) | −25° 29′ 51″ |
In the sky
Visible from the whole Southern Hemisphere and north to latitude 65° N. South of latitude 65° S it never sets. It stands highest at midnight in June, the best time to observe it.
Through a telescope from Earth
Light's journey
The light you see tonight set out 31 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 544 million years.