Sirius (Alpha Canis Majoris)
Sirius (Alpha Canis Majoris) is a star in the constellation Canis Major, magnitude -1.5.
The brightest star in the night sky — a dazzling Dog Star with a tiny, crushed companion at its side.
Nothing in the night sky outshines Sirius except the Moon and a few planets — it is almost twice as bright as Canopus, the runner-up. It earns that partly through power: a white star about twice the Sun’s mass, it gives out 25 times as much light. The rest is closeness. Sirius is one of our nearest neighbours, and it is slowly drifting nearer still.
It does not travel alone. Every 50 years it is circled by Sirius B, a white dwarf — the exposed core of a star that was once the heavier of the pair. That star burned through its fuel, swelled into a red giant, shed its outer layers and collapsed about 120 million years ago. Friedrich Bessel deduced the unseen partner in 1844 from the wobble in Sirius’s path; Alvan Graham Clark first saw it in 1862.
Its name comes from the Greek for ‘glowing’ or ‘scorching’. In Egypt its first dawn appearance each year heralded the Nile flood, and it was worshipped as the goddess Sopdet. The Greeks blamed it for the sweltering ‘dog days’, while Polynesian navigators steered by it across the Pacific.
Sirius (Alpha Canis Majoris) is 8.6 light-years away: the light we see from it set off in 2017, 4 years before the James Webb Space Telescope was launched.
Did you know?
- The first star clocked for speed. In 1868 William Huggins measured Sirius’s motion from the shift of the lines in its spectrum — the first star ever to have its velocity measured. His figure was too large, and had the wrong sign: Sirius is approaching us.
- A southern Pole Star to come. Precession and Sirius’s own motion will carry it to within 1.6° of the south celestial pole around AD 66,270, when it will take a turn as the southern Pole Star.
- Brightest for ages yet. Sirius will brighten slightly over the next 60,000 years, then slowly fade. Even so, it should remain the brightest star in our sky for about 210,000 years, until Vega takes over.
- Loki’s torch. Medieval Scandinavians called it Lokabrenna, ‘burning done by Loki’ or ‘Loki’s torch’. In Sanskrit it is Mrgavyadha, the deer hunter.
The brightest star in the night sky, a brilliant white. Follow the line of Orion’s Belt away from Aldebaran to reach it. When it is low, its twinkling flashes red, green and blue — watch it through binoculars.
When and where to see it
It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in January). It can be seen from everywhere south of 73°N and never sets south of 73°S.
At its highest it stands 23° up from 50°N, 38° up from 35°N, 73° up from the equator, 72° up from 35°S.
Facts
- Type
- Star
- Constellation
- Canis Major
- Designations
- Alpha Canis Majoris, Dog Star, α CMa, 9 CMa, HR 2491, HD 48915, HIP 32349
- Magnitude
- -1.5
- Position
- RA 6h 45.2m, Dec −16° 43′ (J2000)
- Spectral type
- A0mA1Va
- Colour
- white (B−V 0.00)
- Distance
- 8.6 light-years
- Discovered
- Known since antiquity; its white-dwarf companion was first seen by Alvan Graham Clark in 1862
Open AstroPilot to see when Sirius (Alpha Canis Majoris) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.