Manvantaras - Brahma Purana Part-5

A manvantara is an era. There are four smaller eras (yugas) and their names are Satya or Krita Yuga, Treta Yuga, Dvapara Yuga and Kali Yuga. 

Each cycle of Satya Yuga, Treta Yuga, Dvapara Yuga and Kali Yuga is called a mahayuga. A mahayuga comprises of 12,000 years of the gods, or equivalently, 4320,000 years for human. 

71 mahayugas constitute a manvantara and 14 manvantaras constitute a cycle (kalpa). One kalpa is one of Brahma's days and the universe is destroyed at the end of a Kalpa.

Each manvantara is ruled over by a Manu. In the present kalpa, six manvantaras have already passed and the names of the six Manus who ruled were Svayambhuva, Svarochisha, Uttama, Tamasa, Raivata and Chakshusha. The name of the seventh Manu, who rules over the seventh manvantara of the present kalpa, is Vaivasvata.

The titles of the seven great sages (saptarshi) as well as the tile of Indra change from manvantara to manvantara. The gods also change.

In the present vaivasvata manvantara, the seven great sages are Atri, Vashishtha, Kashyapa, Goutama, Bharadvaja, Vishvamitra and Jamadagni. The gods now are the sadhyas, the rudras, the vishwadevas, the vasus, the maruts, the adityas and the two ashvinis.

There will be seven Manus in the future before the universe is destroyed. Five of these Manus will be known as Savarni Manus. The remaining two will be called Bhoutya and Rouchya.