Sadr is the star at the crossing of the Northern Cross in Cygnus, a yellow-white supergiant set in some of the richest fields of the Milky Way.
At a glance
| type | yellow-white supergiant (class F) |
|---|---|
| distance from the Sun | 1,830 light-years (562 pc) |
| its light left it | 1,830 years ago |
| luminosity | 36,100 × the Sun |
| radius | 162 × the Sun |
| surface temperature | 6,250 K |
| constellation | Cygnus (Swan) |
Read off the piece’s own catalogue, the same values it draws with.
About Sadr
Sadr is a supergiant of class F, vastly more luminous than the Sun and swollen to a size that would swallow the orbit of Mercury. It is far more distant than most of the bright stars around it, and appears as bright as it does only because of its huge output.
Its name comes from the Arabic ṣadr, “chest”: it marks the breast of the swan, where the long neck running to Albireo meets the outstretched wings. It is surrounded by glowing hydrogen clouds and dark dust lanes that split the Milky Way here.
What you see in the piece
Sadr is drawn at its true distance, deep in the disc behind the nearer stars of the cross. Switch the band row to gas and the clouds around it light up; in visible light, dust reddens and dims what lies beyond.
Questions
What is the middle star of the Northern Cross?
The middle star is Sadr, Gamma Cygni, a yellow-white supergiant at the point where the swan’s neck crosses its wings.
How far away is Sadr?
Sadr is about 1,830 light-years (562 pc) from the Sun, so the light we see left it 1,830 years ago.