Sirius

Sirius is Alpha Canis Majoris, apparent magnitude -1.46, the brightest star in the night sky by a comfortable margin. Its brilliance is largely a matter of proximity: at 8.6 light years it is one of the nearest stars, and while it is genuinely more luminous than the Sun, about twenty-five times so, it is not an exceptional star in absolute terms. Several stars in this collection are thousands of times more luminous and appear far fainter.

It is a binary. Sirius A is a main-sequence star of type A0, and Sirius B is a white dwarf, the first ever identified. Its existence was inferred by Friedrich Bessel in 1844 from a wobble in the primary's proper motion, and it was seen by Alvan Graham Clark in 1862. Sirius B has roughly the mass of the Sun packed into a volume comparable to the Earth. Its discovery and the subsequent realisation of what it was forced the development of degenerate matter physics and is one of the foundational episodes of twentieth-century astrophysics.

Sirius is low enough in the sky from mid-northern latitudes that atmospheric refraction breaks its light into flashes of colour, and it is the star most often reported to authorities as an unidentified flying object.

There is a genuine and unresolved historical puzzle: several classical sources, including Ptolemy, describe Sirius as red. It is white. Explanations offered include translation and terminology problems, atmospheric effects on a low-altitude star, and, far less plausibly, on stellar evolution timescales, actual change. No explanation is agreed.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy

Sirius has the best-documented practical role of any star in this collection, and it is Egyptian rather than Greek.

The heliacal rising of a star is its first visible appearance in the dawn twilight after a period of invisibility. For Sirius, Sothis in Greek, Sopdet in Egyptian, this occurred in midsummer, and it coincided closely with the annual inundation of the Nile, on which Egyptian agriculture entirely depended. The Egyptians used the event as a calendar marker, and the identification of Sopdet with Isis is old and central.

This produced a real technical problem that is well documented. The Egyptian civil year was 365 days with no leap day, so it drifted against the solar year by about a day every four years, and the civil calendar and the heliacal rising of Sothis came back into agreement only after roughly 1,460 years, the Sothic cycle. Recorded observations of the Sothic rising against the civil calendar are among the anchors used to date Egyptian chronology, though how securely is debated.

The Greek and Roman inheritance is the dog days: the hottest part of summer, coinciding with Sirius's heliacal rising, and blamed on the star. Ancient writers attributed fever, lassitude and madness in dogs to its influence, and the Latin dies caniculares is the source of the English phrase. This is the origin of the Mars component in the star's nature.

Ptolemy assigns Sirius the nature of Jupiter and Mars: Jupiter for honour, wealth and high office, Mars for the heat. Agrippa pairs it with beryl and juniper in the Behenian list.

No account of Sirius is complete without the Dogon material, and it is a case where the evidence has moved decisively and the popular version has not.

The claim is that the Dogon people of Mali possessed, before contact with modern astronomy, knowledge of Sirius B, that it is small, extremely heavy, and orbits Sirius in about fifty years. The source is the French anthropologists Marcel Griaule and Germaine Dieterlen, whose fieldwork from the 1930s onward reported a Dogon cosmology including a companion star called po tolo, made of the heaviest substance and circling Sirius over roughly fifty years. Robert Temple's The Sirius Mystery of 1976 turned this into an argument for extraterrestrial contact, and it has circulated ever since.

The scholarly position has shifted substantially against it. The anthropologist Walter van Beek conducted extended fieldwork among the Dogon in the 1980s and reported that he could not find the Sirius knowledge Griaule described, that informants did not recognise it, that the star-related material was neither secret nor systematic in the way reported, and that Griaule appeared to have shaped his findings through his own questioning. Griaule's methods have been criticised more broadly for producing an unusually coherent cosmology through leading interviews with a small number of informants.

There is also a straightforward contamination route. Sirius B was discovered in 1862, its density established in the 1910s, and its orbital period was in the popular literature well before Griaule arrived; French colonial schools and missionaries were present in the region.

The honest summary: the ethnography is contested, the transmission route is available, and the extraterrestrial reading has no support beyond the disputed ethnography.