Yōga Sūtra 3.29

ध्रुवे तद्गतिज्ञानम्।

dhruvē tadgatijñānam।

[ध्रुवे तत् गति ज्ञानम्।
dhruvē = on polestar; tat = its; gati = relative motion; jñānam = knowledge;]

By (samyama on) the polestar one gains the understanding of its relative motion.