heliacal setting

Heliacal setting refers to the moment when a celestial object, such as the Sun or a star, dips below the horizon just after sunrise or sunset, making it temporarily invisible from a specific location. For example, a star experiencing heliacal sunset would be visible just before dawn and then disappear as the Sun rises, while a heliacal setting occurs when the object becomes hidden after sunset. These events are significant in astronomy and ancient calendars, marking seasonal changes and timekeeping, because they relate to the object's position relative to the Sun as seen from Earth.