an astronomical phenomenon caused by the diurnal rotation of the earth around its axis; the moment a heavenly body crosses the horizon during its transition into the visible half of the celestial sphere, which lies above the horizon. The hour angle t of the celestial body at the moment of ascension is determined by the formula
cos t =-tgφtg δ
where φ is the latitude of the point of observation and 8 is the declination of the celestial body, after which the sidereal time of the ascension is found using the formula
s = α + t
where α is the right ascension of the celestial body (α and δ are taken from astronomical yearbooks). To determine the azimuth A of the celestial body (counted off from the north) at its ascension, the following formula is used:
cos A = sin δ sec φ
(from the two values of t and A, the ones chosen are 180° < t < 360° and 0° < A < 180°). For the precise determination of the moment of ascension of a celestial body, refraction is taken into account.