An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The first rising of → Sirius at dawn shortly before → sunrise. The heliacal rising of Sirius played a significant role in ancient Egypt by heralding the annual flooding of the Nile. The event took place some 70 days after the star had been seen for the last time in the western horizon at sunset. The heliacal rising of Sirius and its association with the rebirth of the Nile was so important that it marked the start of the Egyptian calendar year. At the time, the heliacal rising occurred in early July, as seen from the ancient capital of Memphis. But due to the → precession of the equinoxes the star now reappears in early August in Egypt. The date depends on the latitude (assuming transparent skies), being later for higher latitudes. For latitude 48° it occurs on about August 19.

→ heliacal; → rising; → Sirius.