SB 5.22.6
atha ca yavatardhena nabho-vithyam pracarati tam kalam ayanam acaksate.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thus the time the sun takes to rotate through half of outer space is called an ayana, or its period of movement [in the north or in the south].