Bhagavad Gita Chapter 8 Verse 17 भगवद् गीता अध्याय 8 श्लोक 17 सहस्रयुगपर्यन्तमहर्यद्ब्रह्मणो विदुः। रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जनाः।।8.17।। हिंदी अनुवाद - स्वामी रामसुख दास जी ( भगवद् गीता 8.17) ।।8.17।।जो मनुष्य ब्रह्माके सहस्र चतुर्युगीपर्यन्त एक दिनको और सहस्र चतुर्युगीपर्यन्त एक रातको जानते हैं वे मनुष्य ब्रह्माके दिन और रातको जाननेवाले हैं। Rudra Vaishnava Sampradaya - Commentary In the Puranas the ancient Vedic histories there are statements like: The contemplative, the charitable, the dispassionate and the consequent reach a higher abode that is free from affliction above the material realms of the earthly worlds, the heavenly kingdom and the nether regions. It is known that above the three planetary systems Bhur, Bhuvah and Swah, the planetary system of Maharloka is far superior to the Earth; but if periodic destruction is anyway applicable to all material planetary systems then what is the special distinction. Anticipating such a question and in order to convey that existence on Maharloka lasts for a long duration compared to the much shorter duration of the three previously mentioned lokas or planetary systems being Bhur, Bhuvah and Swar below it. By showing that in each day of the life of Brahma which equal 4 billion, 320 million years and who lives one-hundred years according to this time scale, the material manifestation of the three worlds are created and on each night in the life of Brahma also equalling 4 billion 320 million years the three worlds are dissolved again. Both together total 8 billion 640 million. Such is the proper method of computing time. One year of time on Earth equals one day and one night of the demigods. Computing further in gradation for them and Earth it can be tabulated that one Maha Yuga equals 4,320,000 Earth years but for the demigods that is only a durarion of 12,000 of their years. 1000 such Maha Yugas comprises Brahmas day and another 1000 Maha Yugas comprises his night. Only those who understand time in this frame of reference are actual knowers of day and night. Those beings whose knowledge is restricted to the rotations of the sun and moon are not knowers of day and night for there knowledge is limited. The word yuga in this verse is referring to a Maha Yuga refering to the four yugas of Satya, Treta, Dvarapa and Kali equalling 4 million 320 thousand years. Otherwise combining it with sahasra-yuga would have no relevance to Brahmas day and night. The Vishnu Purana states: Brahmas day consists of 1000 Maha Yugas. The name Brahma also denotes the inhabitants of his planetary system of Maharloka as well. Brahma Vaishnava Sampradaya - Commentary Lord Krishna in order to establish the fact that upon attaining Him there is no further return to the material existence, He cites the potency of His unmanifest Brahman by the example of the cyclic dissolution of creation referring to Brahmas day. The literal meaning for sahasra is one 1000; but actually it means innumerable for in innumerable creations is dissolution taking place periodically. The Brahman or the spiritual substratum pervading all creation is a manifestation of the Supreme Lord and is supreme as well being the shadow of the universal form. Here Lord Krishna speaks of dissolution at the end of Brahmas day. Everything comes into creation by the unmanifest. One Maha Yugas consists of Satya Yuga, Treta Yuga, Dvarapa Yuga and Kali Yuga equalling 4,320,000 years multiplied by 1000 is 4 billion 320 million years and is a day of Brahma. The same duration is his night both combined equal 8 billion 640 million years and which is known as a kalpa.. A year of Brahma is 360 of such kalpas totalling 26 trillion 438 billion and 400 million years and Brahma lives for 100 of these years. The Kurma Purana states: For as long as the life of Brahma is a day for the Supreme Lord and after begins His night. When His night falls everything gets merged back into Him and when His day dawns everything emanates out again and creation begins anew. The Supreme Being who resides in the etheric heart of all beings. Now begins the summation. The word sahasra means 1000 but it also indicative of the Brahman or the spiritual substratum pervading all existence. What is the source of the Brahman? It is emanating from the Supreme Being. Only the periodic cycles of night and day are spoken of in reference to the unmanifest Brahman. When night falls after 4 billion 320 million years everything gets dissolved back into the unmanifest Brahman. Thus from the statement can be drawn a conclusion. At the end of day and night of the four-faced Brahma all the universe is not dissolved, only portions. The Supreme Lord Krishna alone is eternal. He is transcendental to the constructs of time beyond both the night and the day. The night and day of Brahmas lifetime are said to be like the closing and opening of His eyelids Shri Vaishnava Sampradaya - Commentary Those who through the power of yoga or the individual consciousness attaining communion with the ultimate consciousness understand that Brahmasday lasts for 1000 Maha Yugas. Each of which is one cycle of the four yugas or ages combined which are Satya Yuga lasting 1,728,000 Earth years, Treta Yuga lasting 1,296,000 years, Dvarapa Yuga lasting 864,000 years and Kali Yuga lasting 432,000 years all together totalling 4,320,000 years. When multiplied by 1000 Brahmas day equals 4 billion 320 million years. The same total applies also for Brahmas night. So combined one day and one night of Brahma equals 8 billion 640 million years and this is known as a kalpa. One year of Brahma equals 360 of these kalpas totalling 26 trillion, 438 billion and 400 million. Brahma lives for 100 of these years. Kumara Vaishnava Sampradaya - Commentary Those who through the power of yoga or the individual consciousness attaining communion with the ultimate consciousness understand that Brahmasday lasts for 1000 Maha Yugas. Each of which is one cycle of the four yugas or ages combined which are Satya Yuga lasting 1,728,000 Earth years, Treta Yuga lasting 1,296,000 years, Dvarapa Yuga lasting 864,000 years and Kali Yuga lasting 432,000 years all together totalling 4,320,000 years. When multiplied by 1000 Brahmas day equals 4 billion 320 million years. The same total applies also for Brahmas night. So combined one day and one night of Brahma equals 8 billion 640 million years and this is known as a kalpa. One year of Brahma equals 360 of these kalpas totalling 26 trillion, 438 billion and 400 million. Brahma lives for 100 of these years.