Vishnupurana 2.8.47

2.8.47

dakṣiṇe tv ayane caiva viparītā vivasvataḥ //

The relative length of the day or night depends upon the greater or less velocity with which the sun revolves through the degrees between the two points of the horizon. In the solstitial period, in which his diurnal path is quickest, his nocturnal is slowest; and in that in which he moves quick by night, he travels slowly by day. The extent of his journey is in either case the same; for in the course of the day and night he passes through all the signs of the Zodiac, or six by night, and the same number by day: the length and shortness of the day are measured by the extent of the signs; and the duration of day and night by the period which the sun takes to pass through them. In his northern declination the sun moves quickest by night, and slowest by day; in his southern declination the reverse is the case.