He must mean either the heliacal or achronical rising of that sign.
They also possessed lists of the fixed stars, and drew up tables of the times of their heliacal risings.
Swart star: the Dogstar, called swarthy because its heliacal rising in ancient times occurred soon after mid-summer.
This was based upon the heliacal rising of Sirius (Sothis) coincident with the beginning of the inundation.
Implying hereby the Heliacal ascent and Cosmical descent of those stars.
This period, measured thus by the heliacal rising of Sothis, is spoken of as the Sothic cycle.
The dog days were so called because they coincided with the heliacal rising of Sirius or Canicula (the little dog).
The heliacal rising of a constellation is when it comes from under the rays of the sun, and begins to appear before daylight.
I do not see how the heliacal rising of Sirius in any one year could help them to determine its length.
Astronomical data, especially the heliacal risings of Sothis recorded by dates of their celebration in the vague year.