ŚB 5.21.6
Canto 5, Chapter 21, Text 6
यावद्दक्षिणायनमहानि वर्धन्ते यावदुदगयनं रात्रय: ॥ ६ ॥
yāvad dakṣiṇāyanam ahāni vardhante yāvad udagayanaṁ rātrayaḥ.
Word by word
yāvat — until; dakṣiṇa-ayanam — the sun passes to the southern side; ahāni — the days; vardhante — increase; yāvat — until; udagayanam — the sun passes to the northern side; rātrayaḥ — the nights.
Translation
Until the sun travels to the south the days grow longer, and until it travels to the north the nights grow longer.