Srimad Bhagavatam Canto 05, Chapter 20, Text 30

SB 5.20.30

tad-dvipa-madhye manasottara-namaika evarvacina-paracina-varsayor maryadacalo ’yuta-yojanocchrayayamo yatra tu catasrsu diksu catvari purani loka-palanam indradinam yad-uparistat surya-rathasya merum paribhramatah samvatsaratmakam cakram devanam aho-ratrabhyam paribhramati.
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
In the middle of that island is a great mountain named Manasottara, 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 Samvatsara, encircling Mount Meru. The sun’s path on the northern side is called Uttarayana, and its path on the southern side is called Daksinayana. One side represents a day for the demigods, and the other represents their night.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The movement of the sun is confirmed in the Brahma-samhita (5.52): yasyajñaya bhramati sambhrta-kala-cakrah. 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.
Srimad Bhagavatam Canto 05, Chapter 20, Text 29
Srimad Bhagavatam Canto 05, Chapter 20, Text 31