Sirius: the star that started Egypt's calendar
When the brightest star rose just before dawn, the Nile was rising too.
1Sirius is the brightest star in the night sky. Ancient Egyptians noticed that each year, around July, it briefly reappeared on the eastern horizon just before sunrise — an event astronomers call its heliacal rising. That moment coincided with the Nile's annual flood, and the flood's black silt was the lifeblood of Egyptian farming.
2So the Egyptians fixed the start of the year at Sirius's heliacal rising and built a calendar around it: 365 days, twelve months of thirty, plus five festival days. The 365-day frame of the later Roman Julian calendar — and today's Gregorian calendar — traces back to that idea. One star set the rhythm of human days for millennia.
3The Egyptians honoured the star as the goddess Sopdet, shown with a star above her head; the Greeks called her Sothis. Myth, farming and timekeeping were braided together on this one star — in that era, watching the sky was not entertainment but the state's timetable.
Heliacal rising of Sirius = Nile flood + Egyptian new year; the 365-day calendar grew from it.