The Ecliptic is he Sun's path in the heavens. It passes exactly through the center of zodiac longitudinally. The zodiac is a broad band or belt in heavens extending 9 degrees on either side of the Ecliptic. It is an endless circle. In order to measure distances along this circle an arbitrary point is established. This point is called as the first point of Aries. The zodiac revolves once in a day on its axis from east to west. The ecliptic is divided into 12 equal compartments, called the signs of the zodiac. Each compartment covers an arc of 30 degrees. Each sign has its own peculiar qualities, attributed to it by the ancient Maha rishi's after careful and profound observations and meditation.

Each degree of the zodiac is divided into 60 minutes and each minute into 60 seconds. The Vedic seers counted time in Ghatikas and Vighatikas. Other time measuring units are also there but just as minutes and seconds are generally spoken so also are the Ghatikas and Vighatikas are used. 2 &1/2 Ghatikas are equal to 60 minutes or 1 Hour 2 &1/2 Vighatikas =1 minute.

The ecliptic is marked by 27 constellations or Nakshatras called the lunar mansions because the Moon has a special connection with them.

The time taken by the Moon to traverse these 27 stellar mansions is counted as one Lunar month. It is roughly 27.3 days. Each constellation is divided into 4 quarters and are known as the Nakshatras padas. There are in all 108 Nakshatra padas in the zodiac. One pada is equal to 3-1/3degree of celestial arc. The lunar mansions are also called as the Rasis or Radical signs of moon. The Rasis and Nakshatras are reckoned from the same point i.e. zero degree longitude of Aries or Mesha.

The planetary system, which is also known as the solar system or Surya mandala, consists of the Sun and other planets held by the gravitational power of the Sun and they revolve around him. The period of revolution differs according to the size, distance and speed of the planet. The Vedic astrology names the Sun as Ravi, Moon as Chandra, Mars as Mangal, Mercury as Budha, Jupiter as Guru, Venus as Shukra and Saturn as Shani. Besides these, the ascending and descending nodes of Moon (Rahu & Ketu) are also taken as apratyaksha Grahas or invisible influences.

The word Graha is specific to Vedic astrology and it symbolizes the heavenly bodies influencing the life on this earth and is not a classification solar system as Star, Planets, Satellites etc as is done in modern astronomy. Each Graha is the ruler of 3 group of stars and is called as the stellar lord. Thus the 9 Grahas rule the 27 constellations.

According to a very ancient astronomical treatise known as the Surya siddhanta, Saturn is the most distant planet from the Earth. Jupiter, Mars, Sun, Venus, Mercury and Moon come in serial order of their distances from the earth.

Uranus, Neptune and Pluto and other Planets which are found over various periods are not included in Vedic astrology, by the seers for reasons best known to them. It cannot be said that they were unaware of their existence. When they could collect so much of information by Meditation they could also have collected the influence of Uranus etc. Instead they have mentioned the name and qualities of 9 upagrahas which add to the information given by the major Grahas. They took those alone, which influenced the life on this earth. All planets rotate on their own axis and also revolve around the Sun too.

The rate of motion of planets has been worked out:

The Sun moves @ of roughly 1degree a day or takes 3651/4 days for one complete revolution.
Moon = 27 days and 7 hours
Mars = 18 months
Mercury = Requires same time as the sun but his proximity to the sun makes him wobbly and he takes 27 days to cover one zodiacal sign.
Jupiter = 1 year
Venus = has more or less the same velocity as sun
Saturn moves for 30 months in a sign or takes 30 years to make one round.
Rahu and Ketu take 18 months in each sign and complete one round in the reverse motion in 18 years.