Why is Sirius Important?

The star Sirius is also known as the “Dog Star” by virtue of it being prominant in the constellation of Canis Major, or ‘Big Dog’ and is thought to be around 2–300 million years old It can be seen easily from the Northern Hemisphere by the naked eye between 30 and 73 degres of latitude and sometimes its luminosity is so great that it can be seen in daylight.

About Canis Major

Canis Major as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. Next to it are Lepus and Columba (partly cut off).
Canis Major is one of the eighty-eight modern constellations and was included in the 2nd-century astronomer Ptolemy’s classification of 48 constellations.

Sirius is often referred to as one of the dogs following Orion the hunter – the other one being Canis Minor or the ‘lesser dog’. It can be located quite easily by following the line that is naturally formed by the stars of Orions’ Belt down and tp the right a little where the star can easily be identified by its size and brightness.

There are several other fairly bright stars (in order of brightness) in Canis Major, all with Arabic names/ They include Adhara (Virgins), Wezen (The Weight), Murzim (The Announcer), Aludra (The Virgin), Furud (Bright Single One) and Muliphen (Dog’s Ear).

Roman myth refers to Canis Major as ‘Custos Europae’ which is the dog guarding Europa but which happens to fail to prevent her abduction by Jupiter who appears in the form of a bull as well as relating to ‘Janitor Lethaeus’ who is the watchdog.

According to traditional Chinese uranography Canis Major is located within the Southern Quadrant of the night sky and is symbolised as the Vermillion Bird of the South.

About Sirius

Sirius A - Brightest Star in the Night Sky

Not only does Sirius hold a prominant position in Canis Major but it is also the brightest star in the night-time sky with a visual apparent magnitude of -1.47. It is almost twice as bright as the next brightest star, Canopus.

The reason for the brightness of Sirius is not its intrinsic luminosity but is in fact due to its proximity to our own planet.

At a relatively close distance of just 2.6 pc or 8.6 light years Sirius is one of our nearest neighbours. It is roughy twice the mass of our own Sun.

In a mythological sense Sirius was considered to be a dog in its own right whilst early Greek mythology sometimes uses the constellation to represent a two-headed dog.

Sirius as a Binary Star System

Artists Impression of the Relative Sizes of Sirius A and B

During the testing of a new 18.5-inch (470 mm) aperture telescope for Dearborn Observatory American on January 31, 1862 telescope-maker and astronomer Alvan Graham Clark became the first observer of a companion star to Sirius; although suspicions of its existance had first been proposed by German astronomer Friedrich Bessel in 1844.

Sirius B, as yje new discovery came to be called, is one of the more massive White Dwarf stars.

There is currently a great deal of debate as to whether Sirius is not in fact a Binary star system but whether it is actually a Triple system with a much smaller dark star in its proximity.