in astronomy, a term applied to the rising or setting of the stars; or, more strictly speaking, to their emergence out of, and immersion into, the rays and superior splendor of the sun.

A star is said to rise heliacally, when after having been in conjunction with the sun, and on that account invisible, it comes to be at such a distance from him, as to be seen in the morning before sun-rise; the sun, by his apparent motion, receding from the star towards the east: on the contrary, the heliacal setting is when the sun approaches so near a star, as to hide it with his beams, which prevent the fainter light of the star from being perceived; so that the terms apparition and occultation would be more proper than rising and setting.

HELANTHEMUM, in botany, see the article Cistus.