Sothis

Their year originally began when the rapid rising of the Nile coincided with the rising of the star Sirius, called by them Sothis.

Astronomical data, especially the heliacal risings of Sothis recorded by dates of their celebration in the vague year.

This was based upon the heliacal rising of Sirius (Sothis) coincident with the beginning of the inundation.

The twelve months completed, a new year began, whose birth was heralded by the rising of Sothis in the early days of August.