Sirius is the brightest star in the night sky. With a visual apparent magnitude of -1.46, it is almost twice as bright as Canopus, the next brightest star. However, it is not as bright as the Moon, Venus, or Jupiter. At times, Mercury and Mars are also brighter than Sirius.
The name “Sirius” is derived from the Ancient Greek Seirios (“glowing” or “scorcher”). The star has the Bayer designation Alpha Canis Majoris. What the naked eye perceives as a single star is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance separating Sirius A from its companion varies between 8.1 and 31.5 AU.
Sirius appears bright because of both its intrinsic luminosity and its proximity to Earth. The Sirius system is one of Earth’s near neighbors. Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun but has a significantly lower luminosity than other bright stars such as Canopus or Rigel.
The system was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf.
Sirius can be seen from almost every inhabited region of the Earth’s surface (those living north of 73.284 degrees cannot see it) and, in the Northern Hemisphere, is known as a vertex of the Winter Triangle. The best time of year to view it is around January 1, when it reaches the meridian at midnight. Under the right conditions, Sirius can be observed in daylight with the naked eye. Ideally the sky must be very clear, with the observer at a high altitude, the star passing overhead, and the sun low down on the horizon.
Many cultures have historically attached special significance to Sirius, particularly in relation to dogs. Indeed, it is often colloquially called the “Dog Star” as the brightest star of Canis Major, the “Great Dog” constellation. It was classically depicted as Orion’s dog. The Ancient Greeks thought that Sirius’ emanations could affect dogs adversely, making them behave abnormally during the “dog days,” the hottest days of the summer. The Romans knew these days as dies caniculares, and the star Sirius was called Canicula, “little dog.”
Sirius, known in ancient Egypt as Sopdet (Greek: Σῶθις = Sothis), is recorded in the earliest astronomical records. During the era of the Middle Kingdom, Egyptians based their calendar on the heliacal rising of Sirius, namely the day it becomes visible just before sunrise after moving far enough away from the glare of the Sun. This occurred just before the annual flooding of the Nile and the summer solstice, after a 70-day absence from the skies. The hieroglyph for Sothis features a star and a triangle. Sothis was identified with the great goddess Isis, who formed a part of a triad with her husband Osiris and their son Horus, while the 70-day period symbolised the passing of Isis and Osiris through the duat (Egyptian underworld).
Due to its brightness, Sirius would have been noted to twinkle more in the unsettled weather conditions of early summer. To Greek observers, this signified certain emanations which caused its malignant influence. Anyone suffering its effects was said to be astroboletos (ἀστροβόλητος) or “star-struck”. The season following the star’s appearance came to be known as the Dog Days of summer.
The inhabitants of the island of Ceos in the Aegean Sea would offer sacrifices to Sirius and Zeus to bring cooling breezes, and would await the reappearance of the star in summer. If it rose clear, it would portend good fortune; if it was misty or faint then it foretold (or emanated) pestilence. Coins retrieved from the island from the 3rd century BC feature dogs or stars with emanating rays, highlighting Sirius’ importance. The Romans celebrated the heliacal setting of Sirius around April 25, sacrificing a dog, along with incense, wine, and a sheep, to the goddess Robigo so that the star’s emanations would not cause wheat rust on wheat crops that year.
In Sanskrit it is known as Mrgavyadha “deer hunter”, or Lubdhaka “hunter”. As Mrgavyadha, the star represents Rudra. The star is referred as Makarajyoti in Malayalam and has religious significance to the pilgrim center Sabarimala.
Several cultures also associated the star with a bow and arrows. The Ancient Chinese visualized a large bow and arrow across the southern sky, formed by the constellations of Puppis and Canis Major. In this, the arrow tip is pointed at the wolf Sirius. A similar association is depicted at the Temple of Hathor in Dendera, where the goddess Satet has drawn her arrow at Hathor (Sirius).
In Theosophy, it is believed the Seven Stars of the Pleiades transmit the spiritual energy of the Seven Rays from the Galactic Logos to the Seven Stars of the Great Bear, then to Sirius. From there is it sent via the Sun to the god of Earth, and finally through the seven Masters of the Seven Rays to the human race.