The Satya Yuga (Sanskrit: सत्य युग), also called Sat Yuga, or Kṛta Yuga (Sanskrit: कृत युग) in Hinduism, is the first of the four Yugas, the "Yuga (Age or Era) of Truth", when humanity is governed by gods, and every manifestation or work is close to the purest ideal and humanity will allow intrinsic goodness to rule supreme. It is sometimes referred to as the "Golden Age". The Satya Yuga lasts 1,728,000 years. The goddess Dharma (depicted in the form of a cow), which symbolises morality, stood on all four legs during this period. Later on in the Treta Yuga, it would become three, followed by two in the Dvapara Yuga. Currently, in the immoral age of Kali, it stands on one leg.

The Yugas are said to succeed each other almost endlessly. After the perfect Satya Yuga, a decline marks the Treta Yuga. Further decline brings about the Dwapara Yuga, and after it comes the final and dark Kali Yuga, a time of wickedness, when man kills another man. At the end of the cycle Kalki is said to take birth and reestablish righteousness, thus beginning a new Satya Yuga.

...as described in the Mahabharata, a Hindu epic:

Amongst the four eras, the Satya Yuga is the first and the most significant one. Knowledge, meditation, and penance hold special importance in this era.^[1] All the pillars of Dharma are present in totality. During Satya Yuga, all people engage only in good, sublime deeds. Ashrams become devoid of wickedness and deceit. Natyam (such as Bharatanatyam), according to Natya Shastra, did not exist in the Satya Yuga "because it was the time when all people were happy". This Yuga extends up to 1,728,000 years. Lord Vishnu incarnated in four forms i.e. Matsya, Kurma, Varaha and Narsimha in this era.The only text which was considered credible and was followed was Manu’s Dharma Shastra. The average life expectancy of a human being in Satya Yuga was approximately 4000 years.

The Vaishya (traders) of this era shall engage in trade and business very justly and honestly. Brahmins shall be engaged continually in religious sacrifices, study, teaching, charity etc. The Kshatriya (warriors) shall be inclined towards the exhibition of valiance and might. The Shudras shall sincerely serve the Brahmins, Kshatriyas and Vaishyas. This form of religion shall remain intact and absolute in the Satya Yuga.

One shall witness the total establishment of Sanatan Dharma (eternal religion). All the deities, demons, Gandharvas, and Yaksha would give up their hatred and differences. The Rig, Sama and Yajurveda were not separate and demarcated. This era was devoid of agricultural activities or any other type of activity. Just by mere contemplation one would beget desired results. People in this era would never fall ill. No one would try to point out faults or demerits in anyone’s personality. The personality was not plagued by demerits like ego, sorrow, violent thought (aggression), jealousy, hatred, backbiting, fear, anger and lethargy.

At that time, the colour of the Supreme cosmic soul that was situated in the heart of one and all and the saviour of all the sages was white.

All the people that are Brahmins, Kshatriyas, Vaishyas and Shudras were embellished with all the good qualities. People would practice austerities and penance to attain Brahman. All would be inclined towards the supreme knowledge and all actions performed would be in the intention of attaining celestial bliss.

In this way all these divine people would be bestowed with sublime faith and piousness. Albeit, people were segregated on the basis of the Varnashram method, they would all response their faith in the Vedas and the Sanatan Dharma because these people were devoid of selfishness, and they would effortlessly attain sublimity or union with God, which is a salient feature of Satya Yuga. Very valiant, mighty, intelligent and people gifted with all good qualities would be born in this era. They would surprisingly give birth to thousands of children. Great sages embellished with divinity would be born in this era.

The tenth avatar of the Lord Vishnu in the current Mahayuga is foretold to appear at the end of Kali Yuga, the current epoch. The Purana scriptures foretell that Kalki will be atop a white horse with a drawn blazing sword. He is the harbinger of the end time in Hindu eschatology, after which he will usher in Satya Yuga.

Kalki can only be the one whose Birthday/Tithi falls on Dvadasi of Sukla Paksha. This amounts to just 12 days per any given year; furthermore, as it can only be the day of the Lord Sri Maha Vishnu (Chaitra Dwadashi), this amounts to just one day each year or 100 days in the last century.

Indian astrologers have analysed Puranas extensively to try to foretell the time of Kalki's birth. The signs described in the Kalki Purana are as follows:

The Puranas describe the date as twenty-one fortnights from the birth of Krishna, which itself falls on Janmashtami in August. This would put his descent at Vaishakha, between April and May. At this time, the father of Kalki is foretold to be overwhelmed by the incarnation of Godhead that he sees as his son. This places Kalki under the sun sign of Aries or Taurus.

The Bhavishya Purana foretells:

There have been a range of dates predicted, purportedly from different methods of calculation.^[2][3] Sri Potuluri Virabrahmendra Swami, for example, wrote 400 years ago in his Divya Maha Kalagnanam,^[4] or 'Divine Knowledge of the Time,' that Kalki would arrive when the moon, sun, Venus and Jupiter entered the same sign. This is not a rare occurrence and last happened in early 2012, passing without event.^[5] The time of Kalki's arrival has not been consistently asserted by astrologers.^[3]