Aryabhatt Vedic Lessions
Vedic Astrology is based on a very sound understanding of astronomy. In ancient India, astronomy was a highly developed subject. Knowledge of astronomy was considered essential for an astrologer. To the ancient Vedic astrologer, such phenomena as the rotation and the revolution of the earth, the formation of seasons, the occurrence of eclipses, the concepts of solar and lunar months, the equinoxes, and the subtle concepts of disposition of planets and stars in the sky, were all well known. Without the availability of the present day sophisticated instruments and telescopes, he was able to decipher fine variations in the disposition of heavenly bodies. The fact that he could take into consideration such fine divisions of time without the electronic/atomic clocks of today is marvellous.
Earth as the centre
The Vedic astrologer was aware that nothing in the universe was stationary. It was, therefore, irrelevant to attempt to pick up a fixed point in the sky, and consider the movements of earth and other heavenly bodies in relation to such a point. He, therefore, considered the position and movement of all heavenly bodies in relation to the earth itself, which was his residence. It is no wonder then that Indian astronomy and astrology consider the earth as the centre, and all other heavenly bodies moving around it in one manner or the other. The Indian astronomy is thus geocentric and not heliocentric which latter considers the Sun as the centre. The Indian astronomer does appreciate the Sun to be the centre of the solar system, but he also appreciates that the Sun, the solar system, as well as the stars are all moving. Hence he considered the pole star Dhruva as the point of relative fixity at the centre of heavenly bodies in the galaxy. With such profound appreciation of astronomy, one can'ts attribute ignorance of the earthly movements to the ancient Indian astronomer.
Imagine a belt or a path in the sky, some 18 degrees of arc in width, running around the earth in an east-west direction. Groups of stars, to all appearance fixed, are studded along this imaginary belt. Twenty seven (or twenty eight!) such groups of stars are recognised in Vedic astrology. Because of lack of apparent motion, these are called as Nakshatras. This imaginary belt, with nakshatras studded on it, is called the zodiac. The zodiac forms the reference point for fixing up the position of any planet or star in the sky. Since it encircles the earth, it is comprised of 360 degrees. The twenty-seven nakshatras being evenly placed on it each have a span of 13'20' arc. The various nakshatras are numbered from one to twenty-seven.

The zodiac is a 18 deg wide band placed obliquely to the equator.It is divided in 12 rashis and 27 nakshatras.
In contrast to the fixed nakshatras, there are the moving heavenly bodies called the Grahas. These move along the zodiac from the west to the east. They derive their name from the fact that, while moving against the background of the nakshatras, they appear to get hold of one nakshatra after the other (graha = to catch hold of). Vedic astrology recognises nine grahas. They are the Sun, the Moon, Mars, Mercury, Jupiter, Venus, Satrun, Rahu and Ketu. Of these, the Sun is a star, the Moon is a satellite of the earth, Rahu and Ketu are mere mathematical points on the zodiac, while the remaining ones are planets. For the sake of descriptive convenience, we shall refer to all of these as 'planets'. These planets (appear to) revolve around the earth while staying within the limits of the zodiac. The apparent path of the Sun along the zodiac is known as the ecliptic. The ecliptic passes through the centre of the zodiac. It is inclined at an angle of 23'28' to the plane of the equator. The extra-Saturnine planets, called Uranus, Neptune and Pluto has not been considered deliberately as they do not form a part of Vedic astrology.
Signs or Rashis
When the zodiac is divided into twelve equal parts, each such part has an extension of 30 degrees of the arc. Such a division is called a sign or Rashi. A rashi consists of two and a quarter nakshatras. A particular group of stars in the zodiac is considered as the starting point of the zodiac. From this point, the twenty-seven nakshatras or the twelve signs begin. A planet located anywhere along the zodiac may be considered as located in a particular sign, depending upon which twelfth division of the zodiac it is in; it may be considered as being located in a particular nakshatra too, depending upon which twenty seventh division of the zodiac it is in.
The planets from the Sun to Saturn have been allotted the ownership of these signs. While the Sun and the Moon own one sign each, the remaining planets own two signs each. Rahu and Ketu are generally not allotted ownership of these signs. The names of the twelve signs, their planetary lords, and their extent in the zodiac, etc., are given in Table given below :
Table depicting rashis with their lords
Sign English equivalent Symbol Lord Extent in degrees
1 Mesha Aries _ Mars 0-30
2 Vrisha Taurus ^ Venus 30-60
3 Mithuna Gemini ' Mercury 60-90
4 Karka Cancer a Moon 90-120
5 Simha Leo b Sun 120-150
6 Kanya Virgo c Mercury 150-180
7 Tula Libra d Venus 180-210
8 Vrischika Scorpio e Mars 210-240
9 Dhanu Saggitarius f Jupiter 240-270
10 Makara Capricorn g Saturn 270-300
11 Kumbha Aquarius h Saturn 300-330
12 Meena Pisces i Jupiter 330-360
The twenty-seven nakshatras also extend along the zodiac from 0 to 360. They too are owned by planets. But in case of nakshatras, the planets Rahu and Ketu are also allotted the ownership. Each nakshatra is further divided into four parts called the Padas or charanas. There are thus 108 nakshatra padas or quarters in the twenty-seven nakshatras. Each nakshatra quarter measures 320'. The relation of nakshatras with rashis, along with their extent and owners, are shown in Table given below :
Table depicting rashis,nakshatras and their lords
Rashis Nakshatras Extent s d m Pada Lord
1 Mesha 1. Ashwini 0s1320' 4 Ketu
2. Bharani 0s2640' 4 Venus
3. Krittika 1s00' 1 Sun
2 Vrisha 3. Krittika 1s100' 3 Sun
4. Rohini 1s2320' 4 Moon
5. Mrigasira 2s00' 2 Mars
3 Mithuna 5. Mrigasira 2s640' 2 Mars
6. Ardra 2s200' 4 Rahu
7. Punarvasu 3s00' 3 Jupiter
4 Karka 7. Punarvasu 3s320' 1 Jupiter
8.Pushya 3s1640' 4 Saturn
9. Ashlesha 4s00' 4 Mercury
5 Simha 10. Magha 4s1320' 4 Mercury
11. P Phalguni 4s2640' 4 Venus
12. U Phalguni 5s00' 1 Sun
6 Kanya 12. U Phalguni 5s100' 3 Sun
13. Hasta 5s2320' 4 Moon
14. Chitra 6s00' 2 Mars
7 Tula 14. Chitra 6s640' 2 Mars
15.Swati 6s200' 4 Rahu
16. Vishakha 7s00' 3 Jupiter
8 Vrischika 16. Vishakha 7s320' 1 Jupiter
17.Anuradha 7s1640' 4 Saturn
18. Jyeshtha 8s00' 4 Mercury
9 Dhanu 19. Moola 8s1320' 4 Ketu
20. P Asadha 8s2640' 4 Venus
21. U Asadha 9s00' 1 Sun
10 Makara 21. U Asadha 9s100' 3 Sun
22. Shravana 9s2320' 4 Moon
23. Dhanishtha 10s00' 2 Mars
11 Kumbha 23. Dhanishtha 10s640' 2 Mars
24. Sata Bhishaj 10s200' 4 Rahu
25. P Bhadrapada 11s00' 3 Jupiter
12 Meena 25. P Bhadrapada 11s320' 1 Jupiter
26. U Bhadrapada 11s1640' 4 Saturn
27. Revati 12s00' 4 Mercury
A segment of the zodiac extending from 27640'0" to 28053'20" (equivalent to 64'0" to 1053'20" in the Makara rashi, involving the last quarter of the twenty first (i.e. Uttarashadha) nakshatra and the beginning of the twenty-second (Sharavana), is sometimes considered as a separate nakshatra by the name Abhijit. This addition changes the number of nakshatras to twenty-eight. In such a situation, Abhijit is considered as the twent-second nakshatra, and the subsequent six nakshatras (from Sharavana onwards) assume changed numbers (from 23 to 28, instead of 22 to 27).