Chapter 8: Akṣhar Brahma Yog(8.25-8.26)

Chapter 8: Akṣhar Brahma Yog
dhūmo rātris tathā kṛiṣhṇaḥ ṣhaṇ-māsā dakṣhiṇāyanam
tatra chāndramasaṁ jyotir yogī prāpya nivartate||25||
śhukla-kṛiṣhṇe gatī hyete jagataḥ śhāśhvate mate
ekayā yātyanāvṛittim anyayāvartate punaḥ||26||

Meaning : Those who die during smoke, night, the dark fortnight, and the six months of the sun’s southern path (dakṣiṇāyana) reach the lunar light and return again (are reborn).These two paths — the bright (śhukla) and the dark (kṛṣṇa) — are considered eternal. One leads to liberation and no return; the other leads to rebirth.

Chapter 8: Akṣhar Brahma Yog(8.23-8.24)

Chapter 8: Akṣhar Brahma Yog
yatra kāle tvanāvṛittim āvṛittiṁ chaiva yoginaḥ
prayātā yānti taṁ kālaṁ vakṣhyāmi bharatarṣhabha||23||
agnir jyotir ahaḥ śhuklaḥ ṣhaṇ-māsā uttarāyaṇam
tatra prayātā gachchhanti brahma brahma-vido janāḥ||24||

Meaning : O Arjuna (best of the Bharatas), I will now explain the times of leaving the body at which the yogis either do not return or return to this world.Those who die during the time of fire, light, the bright fortnight, and the six months of the sun’s northern path (uttarāyaṇa) go to the Absolute (Brahman); such people know Brahman.

Chapter 8: Akṣhar Brahma Yog(8.17)

Chapter 8: Akṣhar Brahma Yog
sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ
rātriṁ yuga-sahasrāntāṁ te ’ho-rātra-vido janāḥ||17||

Meaning : People who understand the truth know that one day of Brahma lasts for a thousand yugas, and his night also lasts for a thousand yugas. A day of Brahma (the creator) lasts for 1,000 yugas, and his night is equally long. Those who understand this know the vast scale of cosmic time.1,000 yugas = 1 day of Brahma = approx. 4.32 billion years
So 1 full day and night = 8.64 billion years