Heliacal rising / setting
- ancient astrologers gave particular emphasis to the heliacal rising and setting of stars since these could be used as reliable indicators to agricultural conditions. A heliacal setting occurs when a planet or star enters into conjunction with the Sun. The increasing proximity of the Sun towards the star each day eventually leads to a period of invisibility, during which it is masked by the Sun's light (see 'combust'). Its setting is the moment when it is visible for the last time immediately after sunset. It then rises and sets with the Sun, remaining hidden from sight both day and night. When the Sun has separated from the star by somewhere between 8-20 degrees of zodiacal longitude the star begins to emerge, briefly, immediately before sunrise - its first brief appearance being known as its heliacal rising.