WordWeb Online

1. Pertaining to or near the sun; especially the first rising of a star after and last setting before its invisibility owing to its conjunction with the sun
   "the heliacal rising of the Dog Star"; "the heliacal or Sothic year is determined by the heliacal rising of Sothis (the Egyptian name for the Dog Star)"
   - heliac

See also: sun

Encyclopedia: Heliacal