Definition of "heliacal" [he•li•a•cal]

• Of or relating to the sun, especially rising and setting with the sun. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The more precise fixing of new year's day was accomplished through observation of the time of the so-called heliacal rising of the dog-star, Sirius, which bore the Egyptian name Sothis."
• "In some cases the ancients took the sidereal year from the "heliacal" risings or settings of stars, that is from the interval between the time when a bright star was first seen in the morning just before the sun rose, until it was first so seen again; or last seen just after the sun set in the evening, until it was last so seen again."
• "These are the dog days, the days about the heliacal rising of the Dog Star, noted from ancient times as the hottest and most unwholesome period of the year, a period when malevolent influences were thought to prevail."