This rising occurs at Cairo on 19 July ( Julian), placing it just before the onset of the annual flooding of the Nile during antiquity. Its displacement from the ecliptic causes its heliacal rising to be remarkably regular compared to other stars, with a period of almost exactly 365.25 days holding it constant relative to the solar year. The brightest star seen from Earth, Sirius is recorded in some of the earliest astronomical records. The heliacal rising of Sirius marked the flooding of the Nile in Ancient Egypt and the ' dog days' of summer for the ancient Greeks, while to the Polynesians, mostly in the Southern Hemisphere, the star marked winter and was an important reference for their navigation around the Pacific Ocean. Sirius is known colloquially as the ' Dog Star', reflecting its prominence in its constellation, Canis Major (the Greater Dog). The initially more massive of these, Sirius B, consumed its hydrogen fuel and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago. It was originally composed of two bright bluish stars. The system is between 200 and 300 million years old. It is 25 times as luminous as the Sun, but has a significantly lower luminosity than other bright stars such as Canopus, Betelgeuse, or Rigel. Sirius A is about twice as massive as the Sun ( M ☉) and has an absolute visual magnitude of +1.43. After that time, its distance will begin to increase, and it will become fainter, but it will continue to be the brightest star in the Earth's night sky for approximately the next 210,000 years, before Vega, another A-type star and more luminous than Sirius, becomes the brightest star. Sirius is gradually moving closer to the Solar System, so it is expected to increase in brightness slightly over the next 60,000 years, reaching a peak magnitude of −1.68. At a distance of 2.64 parsecs (8.6 ly), the Sirius system is one of Earth's nearest neighbours. Sirius appears bright because of its intrinsic luminosity and its proximity to the Solar System. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.

Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CMa or α CMa. Its name is derived from the Greek word Σείριος, or Seirios, meaning lit. Sirius is the brightest star in the night sky. Dog Star, Aschere, Canicula, Al Shira, Sothis, Alhabor,

Shiira kanji