Arcturus is the brightest star in the northern celestial hemisphere, an orange giant in Boötes that is older than the Sun and moving fast past it.
At a glance
| type | orange giant (class K) |
|---|---|
| distance from the Sun | 36.7 light-years (11.3 pc) |
| its light left it | 36.7 years ago |
| luminosity | 170 × the Sun |
| radius | 25.4 × the Sun |
| surface temperature | 4,290 K |
| constellation | Bootes (Herdsman) |
Read off the piece’s own catalogue, the same values it draws with.
About Arcturus
Arcturus is a giant star: it has used up the hydrogen in its core and swollen to many times the Sun’s width, its surface cooling to orange. It is easy to find by following the curve of the handle of the Plough onwards, the old rule of arcing to Arcturus.
Its composition holds fewer heavy elements than the Sun, and it moves through the Sun’s neighbourhood at an unusually high speed and on a tilted path. Both are signs of an old star that belongs to an older population of the Galaxy than the Sun’s, only passing through.
What you see in the piece
With HUMAN EYE on it is a brilliant orange-gold point, one of the brightest in the sky. Fly to it and the disc grows large and warm-coloured, a giant beside the dwarfs of the neighbourhood.
Measured or modelled
A group of stars sharing Arcturus’s motion, sometimes called the Arcturus stream, has been interpreted as debris from a small galaxy absorbed long ago, or as a pattern raised by the Galaxy’s own bar and spiral arms. The origin is debated.
Questions
How big is Arcturus?
Arcturus has a radius of 25.4 × the Sun and a luminosity of 170 × the Sun.
How do you find Arcturus?
Follow the curve of the handle of the Plough, or Big Dipper, onwards and it leads to Arcturus, the bright orange star of Boötes.