Supernova
HB 21 (SNR G89.0+4.7)
Supernova remnant
The shock wave of a supernova expanding at thousands of kilometres per second: it sweeps up and heats the interstellar gas and shines in radio waves.
| Type | Supernova |
|---|---|
| Constellation | Cygnus |
| Distance | 1,700 pc (5.5 thousand ly) |
| Diameter | 167.6 ly |
| Type | Shell type |
| Radio flux (1 GHz) | 220 Jy |
| Source | Green's SNR Catalogue |
| Right ascension (J2000) | 20h 45m 00.0s |
| Declination (J2000) | +50° 34′ 59″ |
In the sky
Visible from the whole Northern Hemisphere and south to latitude 39° S. North of latitude 39° N 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 5,545 years ago. At that time the first farming villages were being founded; there was no writing yet. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 98 million years.