Sirius (α Canis Majoris) is the brightest star in Earth's night sky and one of the nearest star systems to the Sun, at a distance of approximately 8.6 light-years. It is a binary system consisting of a main-sequence A-type star (Sirius A) and a dim white dwarf companion (Sirius B). The name derives from the Ancient Greek Seiros (Σείριος), meaning “glowing” or “scorching.” Sirius has figured prominently in astronomy, navigation, calendar systems, and mythology across many cultures and historical periods.

Sirius A has a mass approximately 2.1 times that of the Sun, a radius about 1.7 times solar, and a luminosity roughly 25.4 times greater. Its surface temperature is approximately 9,940 K, giving it a blue-white appearance. Sirius B, the companion, was the first white dwarf identified; it has a mass close to that of the Sun compressed into a volume comparable to Earth's. The orbital period of the two stars around their common center of mass is approximately 50 years. The system has no confirmed planets, though the question has not been exhaustively resolved.

Sirius is visible from virtually every inhabited location on Earth and reaches its highest point in the Northern Hemisphere sky during winter months. Its prominence and predictable heliacal rising made it an important calendrical marker in antiquity. Friedrich Bessel observed anomalies in the proper motion of Sirius in the 1840s and correctly inferred the existence of an unseen companion - one of the first successful applications of astrometric methods to detect an invisible stellar body. The companion, Sirius B, was visually confirmed by Alvan Graham Clark in 1862.

Sirius exhibits a relatively large proper motion of approximately 1.34 arcseconds per year and is approaching the Solar System; it will reach its closest point in approximately 61,000 years before receding.

Sirius held significant importance in ancient Egyptian astronomy, where its heliacal rising - its first annual reappearance on the eastern horizon just before sunrise after a period of solar conjunction - coincided closely with the annual Nile flood and anchored the Egyptian civil calendar. In ancient Greece and Rome, its summer appearance was associated with the “dog days,” a period of oppressive heat. It was a navigational reference across many seafaring cultures. A brief account of this history is available on the Sirius - History page.

Several ancient sources - including Ptolemy, Seneca, Horace, and Cicero - described Sirius as red or reddish in color, which conflicts with its present blue-white appearance. Proposed explanations include atmospheric scattering effects when observing stars near the horizon, the possible influence of Sirius B at an earlier evolutionary stage, variation in how ancient writers categorized color, or scribal and translation errors in the textual record. No single explanation commands consensus, and the question remains an active area of historical and astrophysical discussion. See the debate page for competing interpretations.

• Mainstream astrophysics: Sirius is a well-characterized binary system whose properties are reliably established through spectroscopy, astrometry, and photometry. The anomalous ancient color descriptions are considered a historical puzzle without clear resolution. Mainstream Astrophysics Viewpoint
• Archaeoastronomical interpretation: Sirius's role in ancient calendrical and religious systems reflects sophisticated observational astronomy in pre-scientific cultures. Scholars disagree about the extent to which its mythological associations reflect direct astronomical observation versus symbolic convention. Archaeoastronomy Viewpoint
• Dogon controversy: Claims made in the mid-20th century that the Dogon people of Mali possessed ancient knowledge of Sirius B - before its modern discovery - generated significant scholarly debate. The claim is widely disputed on methodological grounds, though it retains currency in some alternative history literature. See the debate page.

• Sirius - History
• Sirius - Red Sirius Debate
• Sirius - Dogon Controversy Debate
• Friedrich Bessel
• Canis Major
• White Dwarf
• Heliacal Rising
• Dog Days

1. Holberg, J. B., et al. “Sirius B: A New, More Accurate View.” Astronomy & Astrophysics 435 (2005): 637-641.
2. Gatewood, G., and H. Gatewood. “A Study of Sirius.” The Astrophysical Journal 225 (1978): 191-197.
3. Bessel, F. W. “On the Variations of the Proper Motions of Procyon and Sirius.” Monthly Notices of the Royal Astronomical Society 6 (1844): 136-141.
4. Schaefer, B. E. “Sirius and the 'Red Sirius' Problem.” Journal for the History of Astronomy 31 (2000): 123-134.
5. van der Waerden, B. L. “The Thirty-Six Stars.” Journal of Near Eastern Studies 8.1 (1949): 6-26.
6. Temple, R. K. G. The Sirius Mystery. London: Sidgwick & Jackson, 1976.
7. van Beek, W. E. A. “Dogon Restudied: A Field Evaluation of the Work of Marcel Griaule.” Current Anthropology 32.2 (1991): 139-167.