Arcturus
Star
Arcturus - the fourth-brightest star in the night sky and the brightest in the northern hemisphere, 36.7 light-years away in Bootes. An ageing orange giant about 25 times the Sun's width and 170 times its light, it is a member of an ancient stream of stars that plunges through the Galactic disk, hinting it was born in another galaxy long ago swallowed by the Milky Way.
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Key facts
Mass
2.15 × 10³⁰ kg
1.08 M☉
Radius
0.118 AU
25.4× wider than the Sun
Surface temperature
4,286 K (4013 °C)
Luminosity
6.51 × 10²⁸ W
Spectral type
K1.5III (orange/red giant)
Science
Physical
- Mass
- 2.15 × 10³⁰ kg · 1.08 M☉
- Radius
- 0.118 AU · 25.4× wider than the Sun
- Density
- 0.0929 kg/m³ · 9.3e-05× water
- Spectral type
- K1.5III (orange/red giant)
Rotation
- Note
- An old, slowly-rotating giant; it shows small brightness oscillations typical of evolved stars.
Composition
- By mass
- An ageing, metal-poorer-than-Sun orange giant about 25 times the Sun's width and 170 times its light. It is a member of the Arcturus stream, a group of stars on unusual Galactic orbits thought to have been accreted from a small galaxy the Milky Way absorbed long ago — so Arcturus may not have been born in our own galaxy's disk.
Temperature
- Surface
- 4,286 K (4013 °C)
Radiation & temperature
- Luminosity
- 6.51 × 10²⁸ W · 170 L☉
- Surface temperature
- 4,286 K (4013 °C)
- Peak wavelength
- 676 nm · red light
Discovery & history
- Method
- Naked-eye star
- Name
- Its IAU name Arcturus is Greek for 'guardian of the bear', from its place behind Ursa Major; it is Alpha Bootis, the brightest star of the Herdsman.
Known and named since antiquity, Arcturus was the first star (other than the Sun) shown to move: in 1718 Edmond Halley found it had shifted since Greek times, proving the 'fixed' stars drift. Its light was famously used to open the 1933 Chicago World's Fair. No planet is known.
Images
Images from open archives · credit shown per image