Canopus: The Second-Brightest Star in the Sky

Canopus at a glance

Why Canopus is so bright

Canopus is much farther away than Sirius, about 310 light-years against 8.6, yet it is almost as bright in our sky. That means it is enormously powerful: a bright giant star of around 8 solar masses, about 70 times the Sun’s diameter and more than 10,000 times as luminous. If Canopus were as close as Sirius, it would rival a crescent Moon. It is a young, evolved star that has moved off the main sequence; it is not quite massive enough to explode as a supernova and will probably end as a heavy white dwarf.

A navigation star for spacecraft

Because Canopus is very bright and lies far from the Sun in the sky, it has long been used by spacecraft to keep their orientation. Star trackers on missions such as NASA’s Mariner and Voyager probes locked onto Canopus as a fixed reference point, together with the Sun. It is also one of the classic navigation stars used by sailors in the southern seas.

Where can you see Canopus?

Canopus lies far south, at a declination of about −53°. It never rises for anyone north of about 37°N: not from London, Paris, New York or Beijing. From the far south of the United States (for example Texas, Florida and southern California), it appears low on the southern horizon on winter evenings. From India it is well seen, low in the south, between December and April; from Australia, South Africa and South America it climbs high, and south of about 37°S it never sets.

The best months are January to March, in the evening. Look for a bright white star well below and to the right of Sirius, from the Northern Hemisphere, or to the left of Sirius and higher from the south. The live tool above shows whether Canopus rises at your location.

Canopus in Indian tradition: Agastya

In India Canopus is called Agastya, after the sage Agastya who, in legend, travelled to the south of India; the star’s appearance low in the southern sky fits the story. Its rising in late summer was traditionally linked to the end of the monsoon season and clearing skies. In Arabic tradition it is Suhail, a bright star associated with the end of the hot season, and in ancient Egypt the city of Canopus gave the star its Greek name.

Constellation Carina

Carina, the Keel, was once part of a giant constellation, Argo Navis, the ship of Jason and the Argonauts, which was later split into Carina, Puppis and Vela. Carina also contains the spectacular Carina Nebula and the unstable giant star Eta Carinae, both rewarding targets for binoculars from southern skies.

Canopus low on the horizon

For observers in northern India, the southern United States, North Africa and the Middle East, Canopus never climbs far above the southern horizon. Seen through a thick layer of air, it often looks reddish and twinkles strongly, flashing different colours, much like Sirius does when it is low. This is an effect of Earth’s atmosphere, not of the star itself, which is white-yellow. From farther south, for example in Australia, South Africa or Chile, Canopus rides high and steady and is visible for most of the year.

Together with Sirius, Canopus helps southern observers find the south celestial pole: the pole lies roughly where a line from Sirius through Canopus is extended, continuing towards the Large Magellanic Cloud.

Frequently asked questions about Canopus

Sources: Canopus overview and references. Star data from standard catalogues; positions and rise/set times are calculated by SpaceTracker.live with the Astronomy Engine library.