Sirius A
Sirius A — the brightest star in Earth's night sky, a hot blue-white A1V star 8.6 light-years away in the constellation Canis Major. About twice the Sun's mass and 25 times its luminosity, it far outshines its tiny companion, the white dwarf Sirius B, with which it shares a 50-year orbit. Its brilliance is as much proximity as power: Sirius is one of the Sun's nearest stellar neighbours.
Key facts
Science
Physical
- Mass
- 4.10 × 10³⁰ kg · 2.06 M☉
- Radius
- 1,192,708 km · 1.71× wider than the Sun
- Density
- 577 kg/m³ · 0.58× water
- Spectral type
- A1V (hot blue-white main-sequence star; formally A0mA1Va)
Orbit (around the system barycenter)
- Semi-major axis
- 6.54 AU
- Eccentricity
- 0.5914
- Orbital period
- 50.13 years
Rotation
- Note
- Rotates in only a few days: its projected equatorial velocity (v sin i ≈ 16 km/s) implies a period of roughly 5.5 days — far faster than the Sun's ~25.
Composition
- By mass
- A hot, hydrogen-burning main-sequence star roughly twice the Sun's mass. Its spectrum shows the 'metallic-line' (Am) peculiarity — enhanced iron-group lines — but it is otherwise a normal young A-type star. At ~9,850 K its light peaks in the blue, giving Sirius its brilliant blue-white colour.
Temperature
- Surface
- 9,845 K (9572 °C)
Radiation & temperature
- Luminosity
- 9.46 × 10²⁷ W · 24.7 L☉
- Surface temperature
- 9,845 K (9572 °C)
- Peak wavelength
- 294 nm · ultraviolet (invisible to the eye)
Discovery & history
- Method
- Naked-eye star
- Name
- Sirius is from the Greek Seirios, 'scorching' or 'glowing'. As the brightest star of Canis Major — the Greater Dog — it is the 'Dog Star'; its late-summer dawn rising gave the ancient world the phrase 'the dog days' of summer.
Sirius has been known and revered since prehistory. To the ancient Egyptians its heliacal rising — the first dawn on which it reappeared after weeks lost in the Sun's glare — heralded the annual flooding of the Nile and anchored their calendar. Greek, Arabic, Chinese and Polynesian traditions all singled it out as the brilliant star of the Greater Dog. In 1718 Edmond Halley found it had shifted since antiquity — one of the first stars shown to have proper motion across the sky.
Images
Images from open archives · credit shown per image