yāvad dakṣiṇāyanam ahāni vardhante yāvad udagayanaṁ rātrayaḥ.

When the sun passes through the five signs beginning with Scorpio, the duration of the days decreases until Capricorn, and then gradually it increases month after month, until day and night become equal in Aries.

Viparyayāni means that the days become shorter and the nights become longer. This will be explained later also.

|| 5.21.6 ||

yāvad dakṣiṇāyanam ahāni vardhante yāvad udagayanaṁ rātrayaḥ.

Until the sun travels on the southern course, the days grow longer, and until it travels to the northern course, the nights grow longer.

Yāvad dakṣiṇāyanam means from uttarāyaṇa until dakṣiṇāyana.

|| 5.21.7 ||

evaṁ nava koṭaya eka-pañcāśal-lakṣāṇi yojanānāṁ mānasottara-giri-parivartanasyopadiśanti tasminn aindrīṁ purīṁ pūrvasmān meror devadhānīṁ nāma dakṣiṇato yāmyāṁ saṁyamanīṁ nāma paścād vāruṇīṁ nimlocanīṁ nāma uttarataḥ saumyāṁ vibhāvarīṁ nāma tāsūdaya-madhyāhnāstamaya-niśīthānīti bhūtānāṁ pravṛtti-nivṛtti-nimittāni samaya-viśeṣeṇa meroś catur-diśam.

The wise teach about the city called Devadhānī, east of Mount Sumeru, possessed by King Indra; a place known as Saṁyamanī, possessed by Yamarāja, to the south of Meru; a place known as Nimlocanī, possessed by Varuṇa, to the west of Meru; and a place named Vibhāvarī, possessed by the moon-go to the north of Meru—which are on the path of the suns revolution on Mānasottara Mount whose circumference is 95,100,000 yojanas. They teach about the sunrise, noon and sunset and midnight in these cities for the purpose of engaging and disengaging people in work according to particular times. They teach about the four directions of Meru.

The circular path is 95,100,000 yojanas The distance from Meru to Mānasottara in both directions (diameter of Mānasottara) 31,500,000 yojanas.[51] The path of the sun’s chariot is 200,000 yojanas wide. Thus the total is 31,700,000 yojanas. Multiplying by three[52] one gets 95,100,000 as the circumference. Experts teach about the city of Indra, east of Meru, on the circumference of Mānasottara Mountain measuring 95,100,000 yojanas in circumference. They teach about the sunrise, noon and sunset in these cities, being in the four directions from Meru. This means the following. Those who reside to the south of Meru (perceive sunrise, and consequently other directions) starting from the east (or eastern city of Indra), those residing in the west perceive sunrise (and the eastern direction) starting from the south, those in the north perceive sunrise starting from the west, and those residing to the east of Meru perceive sunrise starting from the north. It is stated in the Viṣṇu Purāṇa that sarveṣāṁ dvīpavarṣāṇāṁ meruruttarataḥ sthitaḥ: all the inhabitants have Meru in the north (relatively speaking).[53]

 

|| 5.21.8-9 ||