Star cluster
Alessi 21
Open star cluster · 50 million years
An open cluster of stars born together from the same gas cloud in the Milky Way’s disc; the Galaxy’s tidal forces will disperse it within a few hundred million years. Position, distance, age and member count come from the MWSC catalogue; the total brightness is roughly estimated from the member count.
| Type | Star cluster |
|---|---|
| Constellation | Monoceros |
| Distance | 596 pc (1.9 thousand ly) |
| Age | 50 million years |
| Member stars (MWSC) | 100 |
| Reddening E(B−V) | 0.07 |
| Source | MWSC (Kharchenko et al. 2013) |
| Right ascension (J2000) | 7h 10m 40.8s |
| Declination (J2000) | −9° 18′ 00″ |
In the sky
Visible from the whole Southern Hemisphere and north to latitude 81° N. It stands highest at midnight in January, the best time to observe it.
Through a telescope from Earth
Light's journey
The light you see tonight set out around the year 82. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 34 million years.