The great Sankirtan Movement of Lord Caitanya Mahaprabhu is a great gift to the world and a very rare event!
Gauragopala dasa: Many could take it for granted without realizing how rare Lord Caitanya’s appearance actually is as He comes once in every day and night of Brahmā. That is once every 2000th Kali-yuga in the cycle of Maha Yugas, there are 4 Yugas to a Maha Yuga, Lord Caitanya appears “once” in a Kali-yuga with His Sankirtan Movement out of every two thousand.
There are 4,320,000 human years in a Maha Yuga multiply that by 2000 (that equals 8 billion 640 million years) and you will see that Lord Caitanya’s appearance is very rare as He comes once over that enormous period of time
Krishna also comes once every 2000 Maha yugas or every 8 billion 640 million years at the end of Dvarpara-yuga just before Lord Caitanya’s appearance 4,500 years into the Kali-yuga
In this rare Kali-yuga there there is a 10,000 years Golden Age of the Sankirtan Movement of Lord Caitanya Mahaprabhu or the congregational chanting of the Hare Krishna Maha mantra, the previous 1,999 Kali-yugas had no Lord Caitanya or Golden Age of Sankirtan.
The Four Yugas
The four yugas make up a cycle called Divya-yuga or Maha-yuga, which lasts 4,320,000 years.
One thousand of these yugas equal one day of Brahma, which is called a kalpa and another one thousand makes up a night.
Brahma’s lifespan is 100 years of his time and 311 Trillion 400 billion years of our time.
SATYA YUGA - (sometimes also called krta-yuga): The golden age lasts 1,728,000 years. The process of self-realization in this yuga is meditation on Vishnu. During this yuga the majority of the population is situated in the mode of goodness and the average life span at the beginning of the yuga is 100,000 years.
TRETA YUGA - Also called the silver age, lasts 1,296,000 years and the process of self realization is the performance of opulent yajnas(sacrifices). The average life span is 10,000 years and the godly qualities decrease one fourth compared to the Satya yuga.
DVARPARA YUGA - Or the bronze age, lasts 864,000 years and the process of self realization is the worship of the deities within temples. Godly qualities are reduced to 50% by now and the average life expectancy is only 1000 years. Krishna in His originally Form comes at the end of Dvarpara-yuga but not every Dvarpara-yuga as He only comes once in a day of Brahma which is only every 2000th Dvarpara yuga
KALI YUGA - The iron age of hypocrisy and quarrel lasts 432,000 years. Lord Krsna appeared in His original, transcendental form right before the beginning of a Kali-yuga at the end of Dvarpara-yuga in one day of Brahma which is every 2000 cycles of the four yugas. Both Krishna in His original Form and Lord Caitanya do NOT appear in every Maha-yuga. Krishna does not appear at the end of every Dvarpara-yuga and Lord Caitanya does NOT appear in every Kali-yuga as explained above