Vishnupurana 2.8.18

2.8.18

udayāstamanābhyāṃ ca smṛte pūrvāpare diśau
yāvat purastāt tapati tāvat pṛṣṭhe ca pārśvayoḥ //

When the sun (at midday) passes over either of the cities of the gods, on the Mánasottara mountain (at the cardinal points), his light extends to three cities and two intermediate points: when situated in an intermediate point, he illuminates two of the cities and three intermediate. points (in either case one hemisphere). From the period of his rise the sun moves with increasing rays until noon, when he proceeds towards his setting with rays diminishing (that is, his heat increases or diminishes in proportion as he advances to, or recedes from, the meridian of any place). The east and west quarters are so called from the sun's rising and setting there. As far as the sun shines in front, so far he shines behind and on either hand, illuminating all places except the summit of Meru, the mountain of the immortals; for when his rays reach the court of Brahmá, which is there situated, they are repelled and driven back by the overpowering radiance which there prevails: consequently there is always the alternation of day and night, according as the divisions of the continent lie in the northern (or southern) quarter, or inasmuch as they are situated north (or south) of Meru.