Are Rahu and Khedu planets according to Indian Astronomy?
According to Indian Astronomy, there were nine planets (navagraha). They were Sun, Moon, Mars, Jupiter, Venus, Saturn, Rahu and Khedu. Since the ancient Indian Astronomy was developed on the Geocentric foundation (It was believed that Earth was at centre, Sun, moon and planets revolved around the earth), Sun and moon were treated as planets. What about Rahu and Khedu? In Hindu mythology, Rahu is a snake that swallows the sun or the moon for sometime causing eclipses. Ketu is referred to as a ‘shadow’ planet. Are they planets? No. They are imaginary points on the sky.
The earth being a planet revolves around the sun. So the sun appears to move along a great circle on the sky eastward describing about one degree per day relative to stars completing one round in one year. The path of the apparent annual motion of the sun is called the ecliptic. The moon is a satellite of the earth. It moves around the earth tracing a great circle called the lunar orbit. These two circles intersect at two points called nodes. The point where the moon crosses the ecliptic in going north is called the ascending (north) node ,that is Rahu, and the other point where the moon crosses the ecliptic in going south is called the descending (south) node, that is Khedu. These two points are not fixed on the sky but they have a retrograde motion. Why they were considered as important?
A general conjunction of the sun, moon and the planets took place at the midnight between 17th and 18th February, 3102 B.C. The Hindus took this time as the beginning of the epoch Kaliyuga. The Hindu calculations in Astronomy might have begun from this epoch. The Indians knew that the solar and lunar eclipses depend on the positions of moon’s nodes at the time of conjunction and opposition. Eclipses occur when sun and moon are at one these points or very near these points. On a new moon day, solar eclipse occurs surely when the nodal distance (the distance of the sun from a node) is less than 15° 24'. On a full moon day, lunar eclipse occurs surely when the nodal distance is less than 9° 30'. Using this calculation, the Hindu pundits fixed the dates for eclipses with ease. That is why Rahu and Khedu took prominent places in Indian Astronomy. The ancient Indians knew that the same kind of eclipses would be repeated in the same order in a period of 6585 days. The phenomena of the eclipses were given by Bhaskara, a great Astronomer, in his book Sidhanta Siromoni. Arya Bhatta, Brahmagupta and Bhaskara were outstanding Astronomers from India. The Hindu contribution to Astronomy is immense and of great value.
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