The entire creation is one homogeneous Supreme Being. This Being is manifested as this Creation. This creation is made of up of various elements that continuously influence each other. Any two bodies exert a force between them depending on their individual size and also based on their proximity to each other. The larger body will exert a net influence on the smaller body.
This influence between celestial bodies is very much active in the entire creation - One galaxy influencing another, one star influencing another.
Now the proximity of the influencing bodies also does come into play. So for beings living on the Planet earth - the influencing elements are basically the celestial bodies in the Solar System. The physical planets, stars and satellites do influence life on Planet earth. Since the net influence is felt on the planet earth, in Jyotisha we use the Planet earth as the basis to account the influence.
The solar system comprised of the ever luminescent star - The Sun with the planets revolving around the Sun in elliptical orbit. Some of the planets like Earth also have satellites like Moon revolving around the planet Earth and also revolving around the Sun. Each of these planets are influencing the others in some way - large or small but in a definite way.
But as human beings live on the Planet Earth - we use Earth as the basis for accounting the net influence from all the nearby planets, stars and satellites. For all practical purposes of Jyotisha - we'll refer to physical planets, stars and satellites as Grahas or Planets. In the same way, though the planets are revolving around the Sun, in Jyotisha we'll convert this motion of planets around Sun, to be relative to the planet Earth. This'll be referred as the apparent motion of the planets around the planet Earth.
Planets move around the Sun in elliptical orbits. The each planetary plane of revolution is slightly separated from the rest in the vertical direction.
The planet Moon revolves around the planet Earth in its own orbit. This orbit intersects the earth's orbit around the Sun at two points. This is referred to as the North Node(Rahu) and the South Node(Ketu).
Planets
Jyotisha employs the following nine planets.
1) Sun - Surya.
2) Moon- Chandra.
3) Mars- Mangal.
4) Mercury- Budha.
5) Jupiter - Guru or Brihaspati.
6) Venus - Shukra.
7) Saturn- Shani.
8) Rahu and
9) Ketu.
Since Rahu and Ketu are computed points and do not have a physical existence - they are called as Shadow planets or Chhaya Grahas. Yet they play a significant role in all aspects of Jyotisha.
In addition to these planets they are smaller and less influential planetary elements that have been defined. They are called Upagrahas. Planets like Maandi and Gulika are some examples of this class of subplanets.
Eclipses
Eclipses are caused by Sun, Moon and the Earth being in the same plane and in alignment. Viewing from the Earth, Solar eclipses are caused by the Moon covering up the Sun. Thus when the Sun, Moon and Earth align in this order we get the Solar eclipses. This element of alignment is best explained by the involvement of the planet Rahu. Rahu is the point that intersects the Moon's orbit around Earth and Earth's orbit around Sun. The conjunction of Sun, Moon and Rahu causes a solar eclipse.
Lunar eclipses are caused by Earth's shadow being cast on the Moon. Here again Sun, Earth and Moon are on the same horizontal plane and also in alignment. So Sun, Rahu, Earth, Ketu and Moon causes the lunar eclipse.
