Examples from the Web for heliacal
Astronomical data, especially the heliacal risings of Sothis recorded by dates of their celebration in the vague year.
The dog days were so called because they coincided with the heliacal rising of Sirius or Canicula (the little dog).History of the Plague in London|Daniel Defoe
This was based upon the heliacal rising of Sirius (Sothis) coincident with the beginning of the inundation.
Swart star: the Dogstar, called swarthy because its heliacal rising in ancient times occurred soon after mid-summer.The Golden Treasury|Various
He must mean either the heliacal or achronical rising of that sign.Discourses on Satire and on Epic Poetry|John Dryden