Manvantara or Manuvantara or "Manvanter" , or age of a Manu, the Hindu progenitor of humanity, is an astronomical period of time measurement. Manvantara is a Sanskrit word, a compound of manu and antara, manu-antara or manvantara, literally meaning the duration of a Manu, or his life span.
Each Manvantara is created and ruled by a specific Manu, who in turn is created by Brahma, the Creator himself. Manu creates the world, and all its species during that period of time. Each Manvantara lasts the lifetime of a Manu, upon whose death, Brahma creates another Manu to continue the cycle of Creation or Shristi, Vishnu who, on his part, takes a new Avatar, and a new Indra and Saptarishis are also appointed.
Fourteen Manus and their respective Manvantaras constitute one Kalpa, Aeon, or a ‘Day of Brahma’, according to the Hindu Time Cycles and also the Vedic timeline. Thereafter, at the end of each Kalpa, there is a period - same as Kalpa - of dissolution or Pralaya, wherein the world (earth and all life forms, but not the entire universe itself) is destroyed and lies in a state of rest, which is called the, ‘Night of Brahma’.
After that the creator, Brahma starts his cycle of creation all over again, in an endless cycle of creation followed by Absorption for which Shiva, Hindu God of Absorption, and also renewal, is invoked towards the end of each such cycle.
All 14 appointed Indras for each manvantar are: Visvabhuk, Vipascit, Sukirti, Sibi, Vibhu, Manobhuva, Ojasvin, the powerful Bali, Adbhuta, Santi, Ramya, Devavara, Vrsa Rtadhaman, Divassvamin and Suci. These are the fourteen sakras(indras).
The actual duration of a Manvantara, according to the Vishnu Purana is seventy one times the number of years contained in the four Yugas, with some additional years, adding up to 852,000 divine years, or 306,720,000 human years. Seven Rishis, certain (secondary) divinities, Indra, Manu, the king and his sons, are created and perish in one interval (called a Manvantara) equal to seventy-one times the number of years contained in the four Yugas, with some additional years: this is the duration of the Manu, the (attendant) divinities, and the rest, which is equal to 852,000 divine years, or to 306,720,000 years of mortals, independent of the additional period. Fourteen times this period constitutes a Bráhma day, that is, a day of Brahmá; the term (Bráhma) being the derivative form. The Brahma life span is 100 Brahma varshas. The following table will illustrate clearly the link to our years and Brahma years.
(12,000 Deva Vatsaras are defined as, 4,800 Deva Vatsaras of satya yuga, 3,600 Deva Vatsaras of Treta Yuga, 2,400 Deva Vatsaras of Dvapara Yuga and 1,200 Deva Vatsaras of Kali Yuga (which is 1,200 * 360 = 432,000 human years); summing up to 12000)
The first Manu was Svayambhuva Manu. His three daughters, namely Akuti, Devahuti and Prasuti. Devahuti gave birth to one son name kapila and 9 daughters while Prasuti gave birth to Yajna and Akuti gave birth to one son and one daughter. Svayambhuva Manu, along with his wife, Satarupa, went into the forest to practice austerities on the bank of the River Sunanda. At some point in time, Rakshasas attacked them, but Yajna, accompanied by his sons the Yamas and the demigods, killed them. Then Yajna personally took the post of Indra, the King of the heavenly planets.
Saptarshis list: Urjastambha, Agni, Prańa, Danti, Rishabha, Nischara, and Charvarivan. In Svarocisha-manvantara, Lord Vishnu's avatar was called Vibhu.
The second Manu, whose name was Svarocisha, was the son of Agni, and His sons were headed by Dyumat, Sushena and Rochishmat. In the age of this Manu, Rochana became Indra, the ruler of the heavenly planets, and there were many demigods, headed by Tushita. There were also many saintly persons, such as Urjastambha. Among them was Vedasira, whose wife, Tushita, gave birth to Vibhu. Vibhu instructed eighty-eight thousand dridha-vratas, or saintly persons, on self-control and austerity.
Saptarshis list: Kaukundihi, Kurundi, Dalaya, Śankha, Praváhita, Mita, and Sammita. In Uttama-manvantara, Lord Vishnu's avatar was called Satyasena.
Uttama, the son of Priyavrata, was the third Manu. Among his sons were Pavana, Srinjaya and Yajnahotra. During the reign of this Manu, the sons of Vashista, headed by Pramada, became the seven saintly persons. The Satyas, Devasrutas and Bhadras became the demigods, and Sushanti became Indra. From the womb of Sunrita, the wife of Dharma, the Lord appeared as Satyasena, and He killed all the Yakshas and Rakshasas who were fighting with Satyajit.
He was named Tapasa because he was born during Tapasya (deep meditation)
Tapasa/Tamasa, the brother of the third Manu, was the fourth Manu, and he had ten sons, including Prithu, Khyati, Nara and Ketu. During his reign, the Satyakas, Haris, Viras and others were demigods, the seven great saints were headed by Jyotirdhama, and Trisikha became Indra. Harimedha begot a son named Hari by his wife Harini. Hari saved the devotee Gajendra.
Vaikuntha came as Raivata Manu, the twin brother of Tamasa. His sons were headed by Arjuna, Bali and Vindhya. Among the demigods were the Bhutarayas, and among the seven brahmanas who occupied the seven planets were Hiranyaroma, Vedasira and Urdhvabahu.
Saptarshis list: Sumedhas, Virajas, Havishmat, Uttama, Madhu, Abhináman, and Sahishnnu. In Chakshusha-manvantara, Lord Vishnu's avatar was called Ajita.
Ajita came as Chakshsusa Manu, the son of the demigod Chakshu. He had many sons, headed by Puru, Purusa and Sudyumna. During the reign of Chakshusa Manu, the King of heaven was known as Mantradruma. Among the demigods were the Apyas, and among the great sages were Havisman and Viraka.
The seventh Manu, who is the son of Vivasvan, is known as Sraddhadeva(or satyavrata ) or Vaivasvat(son of Vivasvan). He has ten sons, named Iksvaku, Nabhaga, Dhrsta, Saryati, Narisyanta, Dista, Tarusa, Prsadhra and Vasuman. In this manvantara, or reign of Manu, among the demigods are the Adityas, Vasus, Rudras, Visvedevas, Maruts, Asvini-kumaras and Rbhus. The king of heaven, Indra, is known as Purandara, and the seven sages are known as Kashyapa, Atri, Vashista, Angiras, Gautama, Agastya and Bharadwaja. During this period of Manu, Lord Vishnu took birth from the womb of Aditi, the wife of Kashyapa.
In the period of the eighth Manu, the Manu is Surya Savarnika Manu. His sons are headed by Nirmoka, and among the demigods are the Sutapas. Bali, the son of Virochana, is Indra, and Galava and Parshuram are among the seven sages. In the age of this Manu, Lord Vishnu's avatar will be called Sarvabhauma, the son of Devaguhya and Sarasvati.
Saptarshis list: Savana, Dyutimat, Bhavya, Vasu, Medhatithi, Jyotishmán, and Satya. In Daksha-savarnya-manvantara, Lord Vishnu's avatar will be called Rishabha.
The ninth Manu is Daksha-savarni. His sons are headed by Bhutaketu, and among the demigods are the Maricigarbhas. Adbhuta is Indra, and among the seven sages is Dyutiman. Rishabha would be born of Ayushman and Ambudhara.
Saptarshis list: Havishmán, Sukriti, Satya, Apámmúrtti, Nábhága, Apratimaujas, and Satyaket. In Brahma-savarnya-manvantara, Lord Vishnu's avatar will be called Vishvaksena.
In the period of the tenth Manu, the Manu is Brahma-savarni. Among his sons is Bhurishena, and the seven sages are Havishman and others. Among the demigods are the Suvasanas, and Sambhu is Indra. Vishvaksena would be a friend of Sambhu and will be born from the womb of Vishuci in the house of a brahmana named Visvasrashta.
Saptarshis list: Niśchara, Agnitejas, Vapushmán, Vishńu, Áruni, Havishmán, and Anagha. In Dharma-savarnya-manvantara, Lord Vishnu's avatar will be called Dharmasetu.
In the period of the eleventh Manu, the Manu is Dharma-savarni, who has ten sons, headed by Satyadharma. Among the demigods are the Vihangamas, Indra is known as Vaidhrita, and the seven sages are Aruna and others. Dharmasetu will be born of Vaidhrita and Aryaka.
Saptarshis list: Tapaswí, Sutapas, Tapomúrtti, Taporati, Tapodhriti, Tapodyuti, and Tapodhan. In Rudra-savarnya-manvantara, Lord Vishnu's avatar will be called Sudhama.
In the period of the twelfth Manu, the Manu is Rudra-savarni, whose sons are headed by Devavan. The demigods are the Haritas and others, Indra is Ritadhama, and the seven sages are Tapomurti and others. Sudhama, or Svadhama, who will be born from the womb of Sunrita, wife of a Satyasaha.
Saptarshis list: Nirmoha, Tatwadersín, Nishprakampa, Nirutsuka, Dhritimat, Avyaya, and Sutapas. In Deva-savarnya-manvantara, Lord Vishnu's avatar will be called Yogeshwara.
In the period of the thirteenth Manu, the Manu is Deva-savarni. Among his sons is Chitrasena, the demigods are the Sukarmas and others, Indra is Divaspati, and Nirmoka is among the sages. Yogeshwara will be born of Devahotra and Brihati.
Saptarshis list: Agnibáhu, Śuchi, Śhukra, Magadhá, Gridhra, Yukta, and Ajita. In Indra-savarnya-manvantara, Lord Vishnu's avatar will be called Brihadbhanu.
In the period of the fourteenth Manu, the Manu is Indra-savarni. Among his sons are Uru and Gambhira, the demigods are the Pavitras and others, Indra is Suci, and among the sages are Agni and Bahu. Brihadbhanuwill be born of Satrayana from the womb of Vitana.
Almost all literature refers to the first 9 Manus with the same names but there is a lot of disagreement on names after that, although all of them agree with a total of 14.
Modern scientific astronomy estimates the Age of the Universe as around 13 Billion years (13 * 109 years). Conversion of 1 day of Brahma into human years yields 8.58816 * 109 years (derived as 2 kalpas * 14 Manvantaras * 71 Chaturyugas * 12,000 Deva vatsaras * 360 human years). According to Vedas, there are 504 000 Manus manifested during the lifetime of one Brahmā (311,040,000,000,000 human Earthly years), 5040 Manus in one year of Brahma, and 420 Manus in one month of Brahma. (See for more details: List of numbers in Hindu scriptures.)