Bhagavatapurana 5.21.3

5.21.3

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yan-madhya-gato bhagavāṃs tapatāṃ patis tapana ātapena tri-lokīṃ pratapaty avabhāsayaty ātma-bhāsā sa eṣa udagayana-dakṣiṇāyana-vaiṣuvata-saṃjñābhir māndya-śaighrya-samānābhir gatibhir ārohaṇāvarohaṇa-samāna-sthāneṣu yathā-savanam abhipadyamāno makarādiṣu rāśiṣv aho-rātrāṇi dīrgha-hrasva-samānāni vidhatte //

3. Placed at its centre, the glorious Sun, Lord of luminaries, warms the three worlds with his heat and lights them with his rays. Under the names of Uttarayana, Dakshinayana, and Vaishuvata (Vishuvat) on account of his slow, rapid and equal marches and in his positions of upward course, downward course, and his course in a straight line, which he attains in due seasons, namely, at the several signs of the Zodiac (commencing with the Capricorn), the Sun makes days and nights, longer, shorter, or equal, as the case may be.