Srimad-Bhagavatam: Canto 5 - Chapter 1 - Verse 30

Sanskrit:

तद्‌द्वीपमध्ये मानसोत्तरनामैक एवार्वाचीनपराचीनवर्षयोर्मर्यादाचलोऽयुतयोजनोच्छ्रायायामो यत्र तु चतसृषु दिक्षु चत्वारि पुराणि लोकपालानामिन्द्रादीनां यदुपरिष्टात्सूर्यरथस्य मेरुं परिभ्रमत: संवत्सरात्मकं चक्रं देवानामहोरात्राभ्यां परिभ्रमति ॥ ३० ॥

ITRANS:

tad-dvīpa-madhye mānasottara-nāmaika evārvācīna-parācīna-varṣayor maryādācalo ’yuta-yojanocchrāyāyāmo yatra tu catasṛṣu dikṣu catvāri purāṇi loka-pālānām indrādīnāṁ yad-upariṣṭāt sūrya-rathasya meruṁ paribhramataḥ saṁvatsarātmakaṁ cakraṁ devānām aho-rātrābhyāṁ paribhramati.

Translation:

In the middle of that island is a great mountain named Mānasottara, which forms the boundary between the inner side and the outer side of the island. Its breadth and height are 10,000 yojanas [80,000 miles]. On that mountain, in the four directions, are the residential quarters of demigods such as Indra. In the chariot of the sun-god, the sun travels on the top of the mountain in an orbit called the Saṁvatsara, encircling Mount Meru. The sun’s path on the northern side is called Uttarāyaṇa, and its path on the southern side is called Dakṣiṇāyana. One side represents a day for the demigods, and the other represents their night.

Purport:

The movement of the sun is confirmed in the Brahma-saṁhitā (5.52): yasyājñāya bhramati saṁbhṛta-kāla-cakraḥ. The sun orbits around Mount Sumeru, for six months on the northern side and for six months on the southern. This adds up to the duration of a day and night of the demigods in the upper planetary systems.