Sirius

Where the name comes from

Sirius comes from the Greek seirios, meaning scorching or searing, which is a fair description of the brightest star we can see. It sits in Canis Major, the big dog that follows Orion across the sky, so English speakers often just call it the Dog Star.

The Dog Days of summer

The ancient Greeks and Romans noticed that Sirius rose with the Sun through the hottest weeks of the year. They decided the star and the Sun were piling their heat together, and called that stretch the Dog Days, a phrase we still use for a sluggish, sweltering summer. Sirius was not adding any warmth at all. People connected the dots between two things that happened at once, and the name stuck for two thousand years.

Why it looks so bright

Sirius shines for two reasons at the same time. It is genuinely luminous, around twenty five times brighter than the Sun, and it is close, only about eight and a half light years away. Almost every other star you could name is far more distant, which is why this one wins.

The hidden companion

In 1844 an astronomer noticed Sirius was wobbling slightly, as if something were tugging on it. Eighteen years later a telescope maker finally saw the culprit, a tiny, incredibly dense companion now called Sirius B, or the Pup. It is a white dwarf, the burnt-out core of a dead star, packing roughly the mass of the Sun into a ball the size of Earth.

What it meant to Egypt

For the ancient Egyptians, Sirius was the single most important star. Each year it disappeared behind the Sun for about seventy days, then rose again just before dawn, and that first dawn rising fell right as the Nile began its annual flood, the event their whole harvest depended on. They built their calendar around the rising of this one star.