Canis Major
What is Canis Major?
Constellations· Winter evenings (N) · southeast of Orion's belt, the brightest star. Orion's great hunting dog. Sirius, the brightest star in the night sky, sits at its collar, with Adhara and Wezen below forming the body. Ancient Egyptians used the first dawn rising of Sirius to tell when the Nile would flood.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Sirius | -1.5 |
| Adhara | 1.5 |
| Wezen | 1.8 |
| Mirzam | 2.0 |
| Furud | 3.0 |
| Omicron2 Canis Majoris | 3.0 |
The 6 brightest of the 9 stars used in the figure (8 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | winter evenings, January–March |
|---|---|
| Brightest star | Sirius (−1.5, brightest star in the sky) |
| How to find | extend Orion's belt southeast |
| Area rank | 43rd of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
The riddle of the red Sirius in old records
In the second century Ptolemy's Almagest listed Sirius among the reddish stars, and the Roman philosopher Seneca also called it red. Today, though, Sirius is plainly blue-white, and old Chinese records consistently describe it as white. Whether the star's colour really changed within two thousand years was debated for a long time, and some even proposed that its companion, Sirius B, was then a red giant.
Astronomers reject that idea, because turning a red giant into a white dwarf takes far longer than a few thousand years. A different explanation is now favoured: when Sirius is low near the horizon, the atmosphere reddens its light just as it reddens the setting Sun, and ancient writers may have recorded that view. The riddle is solved not by the star itself but by looking at the sky and language of the people who wrote about it.
The constellation in depth
Canis Major is the dog that follows the hunter Orion, sometimes said to be Laelaps, the legendary hound that never failed to catch its prey. The name Sirius means scorching in Greek. In the ancient Mediterranean, Sirius rose with the Sun at dawn in midsummer, so the hottest days of the year came to be called the dog days.
Sirius looks so bright mainly because it is close, about 8.6 light-years away, one of the nearest stars visible to the naked eye. A small companion, Sirius B, circles it about once every 50 years. Sirius B is a white dwarf, the leftover core of an old star, about the size of Earth but with roughly the mass of the Sun.
There is more to see. Adhara, in the dog's hind leg, is the brightest star in the sky in ultraviolet light. The constellation also holds VY Canis Majoris, a red hypergiant and one of the largest stars known, and just below Sirius the open cluster M41 shows well even in binoculars.
On winter evenings, extending the line of Orion's belt to the south-east leads to brilliant Sirius. From mid-northern latitudes such as London or New York it stays fairly low, and its light passes through unsteady air, so it seems to flash in many colours. With the Sky view set to a February evening, the whole dog appears in the southern sky.
Frequently asked
- When can I see Canis Major?
- Canis Major is best seen in winter evenings, January–March.
- How do I find Canis Major?
- To find Canis Major, look for extend Orion's belt southeast.
- What is the brightest star in Canis Major?
- The brightest star in Canis Major is Sirius, at magnitude -1.5.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.