Arcturus
Where is Arcturus?
Look west, about 15° up at 20:20 in Boötes. It sinks lower through the evening and sets at 22:06.
- Rises
- 06:30
- Highest
- 14:20
- Sets
- 22:06
- Best after dark
- 20:20 · 15°
Can I see Arcturus tonight?
From London tonight, Arcturus is above the horizon after dark. It’s highest soon after dark, around 20:20, in the west at 15°.
At magnitude −0.1 it is one of the brighter points in the sky, easy to see by eye when it’s clear.
This is position and timing only: clouds, haze and light pollution aren’t included.
What does Arcturus look like?
Arcturus looks orange to the eye. Its spectral type is K2IIIp: orange giant (cooler than the Sun).
Eyes
A bright star with a clear golden-orange color.
Binoculars
The orange tint becomes richer and easier to see.
Telescope
A bright orange point. There is no companion to split.
About Arcturus
Arcturus is the brightest star in the northern half of the sky and the fourth-brightest overall. It is an orange giant about 37 light-years away, a star that has used up the hydrogen in its core and swollen to around 25 times the Sun’s width.
Its name means “guardian of the bear”, because it seems to follow Ursa Major, the Great Bear, around the pole.
Arcturus moves unusually fast across the sky compared with most bright stars. It belongs to an old group of stars passing through the Sun’s neighborhood, possibly the remains of a small galaxy absorbed by the Milky Way long ago.
Arcturus has only about as much mass as the Sun, but it is far larger and well over 100 times more luminous. It is an old star, billions of years older than the Sun, and shows what our Sun may become billions of years from now.
In 1933, light from Arcturus was captured by a telescope and used to switch on the lights at the Chicago World’s Fair.
Arcturus in Boötes
Questions
Why is Arcturus orange?
How do I remember how to find Arcturus?
Sources: SkyMate; Wikidata (CC0). Positions computed for your place and time with astronomy-engine. Data & Licences