 Vedic Astrology is based on a detailed understanding of naked-eye observational astronomy. Astronomy is highly developed in Vedic culture, and it is essential for astrologers to have an intuitive grasp of the astronomical concepts and relationships underlying Jyotish. This course introduces the Vedic astronomical system that forms the basis of Jyotish. A planetarium software program like Stellarium (pictured above) can help with visualizing the planets and constellations as they are at any place and time. |
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Vedic Astronomy
The Zodiac is the path that the planets follow as they move relative to the background of fixed stars. You can visualize the Zodiac as a belt in the sky, about 18 degrees of arc in width, running around the earth in an east-to-west direction. Several groups of fixed stars are studded along this imaginary belt, divided into groups called Rāśis and Nakṣatras. 
The most basic Vedic astronomical concepts used in Vedic astrology require an understanding of the earth, its movements, and the apparent movements of the planets around the earth. Putting all these in perspective is basic to visualizing the cosmic situation abstracted in an astrological chart.
When the Zodiac is divided into twelve equal parts, each part extends over 30 degrees of arc. Such a division is called an astrological sign or Rāśi. A Rāśi consists of two and a quarter Nakṣatras. A particular group of stars in the Zodiac is considered as the starting point of the Zodiac and the twenty-seven Nakṣatras and the twelve Rāśis begin from this point. A planet located along the Zodiac is located in a particular Rāśi, according to which division of the Zodiac it is in; it is also located in a particular Nakṣatra, depending upon which twenty-seventh division of the Zodiac it is in. 
The earth rotates around its axis from west to east once every twenty-four hours. Therefore, the entire sky, including the Zodiac, with its fixed Rāśis and Nakṣatras, appears to revolve around the earth from east to west every twenty-four hours. Thus all the Rāśis and Nakṣatras of the Zodiac appear to rise on the eastern horizon and set on the western horizon in the course of every day.
The earth rotates around its axis in 24 hours; this is called a mean solar day. A sidereal day is 3 minutes and 56 seconds, or roughly 4 minutes shorter than the mean solar day. Why is the mean solar day longer than the sidereal day?
The Vedic seers used an elaborate method of reckoning time. They combined genius with religion so that it appeals to the intellectual and the devotee alike. 
The vernal equinox moves westward at a rate of approximately 50.26 seconds of arc each year. This precession causes a slow increase in the right ascension of the Zodiac. This precession takes 25,800 years to complete one circle. That Vedic Astrology takes this gradual precession into account is the principal difference between it and Western astrology.
