1. relating to or determined by the position of the sun, especially the rising or setting of a star or planet in relation to the sun
Usage: astronomy; technical

Examples

• The heliacal rising of Sirius marked the beginning of the ancient Egyptian year.
• Astronomers tracked the heliacal setting of Venus to predict seasonal changes.
• The heliacal appearance of a star occurs when it becomes visible just before sunrise.
• Ancient civilizations used heliacal observations of celestial bodies for calendar systems.
• The heliacal conjunction of Jupiter and the sun made the planet invisible from Earth for several weeks.