Definition

1. Adjective:
   • Pertaining to or near the sun: Relating to the sun or its proximity.
   • Relating to the first or last visibility of a celestial body with respect to the sun: Specifically describes the first rising of a star just before sunrise or its last setting just after sunset, after a period of being invisible due to its conjunction with the sun.

Usage Examples

• Adjective:
  • Ancient Egyptian priests carefully observed the heliac rising of Sirius to mark the beginning of their calendar year.
  • The heliac setting of a planet marks its final disappearance from the evening sky as it moves behind the sun.
  • Determining the heliac rising of a star requires precise knowledge of its position relative to the sun.

Advanced Usage

• "Heliacal": This is the more common and precise adjectival form, often used interchangeably with "heliac" in technical contexts.
  • The heliacal rising of the Pleiades was an important agricultural marker for many ancient cultures.
• "Heliacal year": A year defined by the interval between successive heliacal risings of a specific star, such as the Sothic year.
  • The Egyptian Sothic year was a heliacal year based on the star Sirius.

Variants and Related Words

• Heliacal (adj): The standard adjectival form meaning "pertaining to the sun," especially in an astronomical context.
• Heliacally (adv): In a heliacal manner.
  • The star appears heliacally just before dawn.

Synonyms

• Solar: Of, relating to, or determined by the sun. (Note: "Solar" is a broader term, while "heliac(al)" is specific to celestial visibility events.)
• Sun-related: Pertaining to the sun.

Notes on Meaning

• The term "heliac" is highly specialized and used almost exclusively in historical and astronomical contexts to describe the precise timing of a star's appearance or disappearance relative to the sun's glare. It is not used in general conversation about the sun. The form "heliacal" is more frequently encountered in modern texts.

Adjective

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)