The Vedas are primary source of knowledge and are oldest known literary documents of the world. These are the final authority in almost all matters of Hindu society. Sri Swami Dayananda Saraswati gave new interpretation of Vedas to the modern world and stated that they possess secrets of science, still modern scientists are unraveling the truths behind them.   The word Veda is formed from the root "Vid. It means academically to know, acquire, deliberate, live and subsist. These are the sacred books of Hindus that contains knowledge of nature, religion, morals and spiritual sciences. Interpretation of the Vedas are broadly done on three levels viz: first is on cosmological, second is on the ritualistic (i.e. Yajnas, Yagas etc) and third is on spiritual. Vedas are monotheistic and are arranged in four samhitas viz Rigveda, Yajurveda, Samaveda and Atharvaveda. Each of the four Vedas are divided into several parts and the nomenclature of these differs from one another. All Vedas put together contain approximately 20349 mantras. The Vedic text was revealed in the Divine language, called Sanskrit. As the Vedas are not easily understood by the people, elaborate Brahmanas were written by intellectual Rishie.   i) The Brahmanas: These are mostly expositions of Vedas with additional rituals and historical disquisitions, connected with the teachings of Vedas. There are forty (40) known Brahmanas. However, only sixteen (16) of them survived. Most important among them are Shatapatha, Aitreya, Gopatha and Tandya belonging to the Yajurveda, the Rigveda, the Atharvaveda and the Samaveda respectively. The other twenty four (24) Brahmanas are lost. Each Brahmana is attached to a particular Shakha (branch) of the Veda. Later a class of thinkers (seers) arose, who took some portion of the Vedas and the Brahmanas dealing with metaphysical matters, such as the concept of God, Soul, explained them as philosophical disquisitions. These are known as Upanishads.   ii) The Upanishads: There are one hundred and eight (108) Upanishads. Out of which twenty (20) are said to be important and eleven (11) among them are principal ones viz: the Isha, Katha, Kena, Prashna, Aitreya, Tattieya, Mundaka, Mondukya, Chhandugya, Brihadadaranyaka and Shwetashwatara The Upanishads contain realized experiences. They are as a whole consistent with Vedas. In them one finds the ancient Vedic heritage presented with Vedic flavour. Later we have four Upavedas, as vedic sciences.   iii) The Upavedas: These are in four viz: Ayurveda (Science of Medicine), Arthaveda (Sociology, Economics and Political Science), Dhanurveda (Science of war) and Gandharvaveda (Science of Music). Besides these we have six systems of Philosophy as the Upangas.   iv) The Upangas: These are six viz: (1) Nyaya (Logic) by Gauama,(2) Vaisheshika by Kanada, (3) Yoga by Patanjali, (4) Sankhya by Kapil,(5) Purva Mimansa by Jainmini and (6) Uttara Mimansa by Badarayana i.e. Vyasa. At the end we have six Vedangas as Vedic knowledge.   v) The Vedangas: These are also six viz: (1) Shiksha (Phonetics), (2) Kalpa (Rituals), (3) Vyakarana (Grammar). (4) Nirukta (Etymology), (5) Chhandas (Meters) and (6) Jyotisha (Astrology & Astronomy).   It is an admitted fact universally that starting from Brahmanas to Vedangas as works of later vedic time. These are considered as Vedic heritage and no one includes them in the Vedas. Jyotisha is a Vedanga, ie a limb of Vedas. It means knowledge of 'Jyoti' or 'light', the root cause of all creations. Jyotish Shastra is the study of heavenly bodies and their influence on human life and mundane events.