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heliacal rising(hi-lÿ-ă-kăl) The first appearance of a star or planet in the eastern sky just before dawn, following a period when it has been too close to the Sun to be visible. A heliacal setting is the last occasion on which a star or planet can be seen in the western sky just after sunset prior to its becoming too close to the Sun to be seen.
heliacal rising[hi′lī·ə·kəl ′rīz·iŋ]
The rising of a celestial body at the same time or just before that of the sun.