The Rig-Veda (Praising Knowledge) is part of the Hindu Vedas; these religious scriptures consist of 1,017-1,028 hymns (many intended for sacrifical rituals), contained in 10 books (Mandalas). Prominently mentioned, within the Rig-Veda, are the gods Agni, Dyaus Pitar, Indra, Prithivi Mater, Vishnu; as well as the sacred Soma. The Rig-Veda was completed by 1500 BC. (Fisher)
The first notable Western Vedic student, Max Müller noted that the Rig-Veda had been composed over a long period (perhaps 800 years -- Fisher). For Müller, the Rig-Veda was the only real Veda; he argued that the others (particularly the Yajur-Veda and Sama-Veda) contained, primarily, paraphrases and quotations.
The Rig-Veda is a long collection of short hymns devoted to the praise of the gods. It details the earliest form of Hinduism, sometimes referred to as the 'Vedic' or Aryan stage of the religion, which is closely tied to the pre-Zoroastrian Persian religion. It is thought that Zoroastrianism and Vedic Hunduism evolved from an earlier common religious culture. According to some writers, following the Indian scholar Tilak and later writers, astronomical references date the Rig-Veda to the 4th or 5th millennium BC. Other scholars continue to accept Müller's dating. The Upanishads are assumed to be of a much later date than the original Samhitas. It generally accepted that at least a thousand years separate the oldest and newest portions of the Vedas.
The Rigveda is of interest because it describes a very early stage in the evolution of Hinduism. Its hymns were composed over a long period. Scholars date it to the second millennium BC by relating it to the Aryan invasion theory. The astronomical references in the Rigveda date to the third and the fourth millennium BC. There is also the question of the reference to the Sarasvati river, lauded as the greatest river flowing from the mountain to the sea. Archaeologists have concluded that the river went dry perhaps before 2600 BC or certainly before 1900 BC.
The names of gods and goddesses found in the Rigveda are found amongst many other Indo-European speaking people as well. This also indicates the text's antiquity.
According to the Shatapatha Brahmana, the number of syllables in the Rigveda is 432,000, equalling the number of muhurtas (1 day = 30 muhurtas) in forty years. This statement stresses the underlying philosophy of the Vedic books that there is a connection (bandhu) between the astronomical, the physiological, and the spiritual.
The authors of the Brahmana literature described and interpreted the Rigvedic ritual. Yaska was an early commentator of the Rigveda. In the 14th century, Sayana wrote an exhaustive commentary on it. More recently, Swami Dayananda, who started the Arya Samaj and Sri Aurobindo have emphasized a spiritual (adhyatimic) interpretation of the book. Subhash Kak has shown an astronomical code in the organization of the hymns.
The Rigvedic view considers the universe to be infinite in size. It divides knowledge into two categories: lower (related to objects) and higher (related to the perceiving subject). The lower knowledge is taken to be beset with paradoxes whereas higher knowledge is not.