|1. Sun (Surya)||2. Moon (Chandra)||3. Mars (Mangal)
|4. Mercury (Budh)||5. Jupiter (Guru)||6. Venus (Shukra)
|7. Saturn (Shani)||8. Dragon's head (Rahu)||9. Dragon's Tail (Ketu)
Illuminating celestial bodies in sky which are stationary are called as constellations & which have mobility are called as planets. Constellations are clusters of stars. Stars continue to blink whereas glow of planets is always the same. Stars illuminate with there own light whereas planets illuminate by the light of Sun.
In Indian Vedic Astrology importance has been given to 9 planets: - Sun or Surya, Moon or Chandra, Mars or Mangal, Mercury or Budh, Jupiter or Guru, venus or Shukra, Saturn or Shani, Dragon's head or Rahu & Dragon's Tail or Ketu.
What are Rahu & Ketu?
In Indian Vedic Astrology Rahu & Ketu have been considered as planets but they don't have any physical existence in actual. They are imaginary planets which are considered as always retrograde & always combust. Moon revolves around the Earth & Earth along with Moon revolves around Sun. Moon while revolving around Earth intersects the Earth's circumference on two points. It means the orbit of Earth & Moon interects each other on two points in which one is called Rahu which is seen to be going from bottom to top & the other point which is just opposite to Rahu is called as Ketu. Rahu is called as 'Ascending Node' & ketu is called as 'Descending Node'.
Orbit of Earth is actually orbit of Sun (from the point of view of relative motion) which is also called as Ecliptic. Moon while revolving around Sun intersects ecliptic at two points making an angle of 5°. This is termed as Celestial Latitude.
There is a famous story in Indian Mythology about Rahu & Ketu. While the churning of Sea a demon secretively drank elixir & became immortal. Indra got angry by this & separated the head of the demon from his body by cutting it. But the demon didn't die because he became immortal by drinking elixir. Head of the demon was termed as Rahu & body of the demon was termed as Ketu. These Rahu & Ketu are always running after Surya (Sun) & Chandra (Moon) & many times eclipse them because Surya & Chandra revealed about the drinking of elixir by the demon to Indra.