First Sign of the Zodiac
When the sun passes through Mesa [Aries] and Tula [Libra], the durations of day and night are equal. When it passes through the five signs headed by Vrsabha [Taurus], the duration of the days increases [until Cancer], and then it gradually decreases by half an hour each month, until day and night again become equal in Libra.

Srimad-Bhagavatam 5.21.4
A.C. Bhaktivedanta Swami Prabhupada