In both Astrology and Historical Astronomy the Zodiac belt is the great circle of twelve 30° divisions of celestial longitude that are centered upon the ecliptic in which our Sun apparently moves month by month throughout the year transcribing the energy of those different constellational signs and thereby transmitting the celestial radiations to our Earth. The paths of the Moon and visible planets also remain close to the ecliptic, within the belt of the zodiac.
The zodiac is a celestial coordinate system which takes the ecliptic as the origin of latitude and the position of the sun at vernal equinox as the origin of longitude.
The Zodiac is divided into twelve equal divisions, since zodiac consists of 360° , each division will consist of 360° / 12= 30°. The divisions are known as Rashis for the purpose of astrology which are named after the imaginary figures which the stars form in each division.
Our sages identified twelve groups of stars separated approximately 30° each in the 360° celestial sphere. Thus we have 12 Rashis. They divided the celestial sphere in 12 parts because moon moves around earth 12 times during the time earth revolved round the sun.
Vedic Astrology also uses a Lunar Zodiac of 27 Lunar Signs called Nakshatras. This Lunar Zodiac is incredibly ancient, magical and powerful. Looking at the daily movement of Moon, sages also identified 27 constellations (Nakshatras) around the celestial sphere called Ashwini, Bharni etc. They are separated by 360° /27= 13° 20'. Every day Moon crosses over one constellation. Start of Ashwini matches with the start of first sign Aries.
From earth we see a celestial body passing over a sign, this helps us know the location of that body. In astronomy we define planet as a celestial body which revolves round the Sun and a body which revolves round a planet is called a satellite. Sun is termed as a star.
In astrology planet is defined differently. Since man lives on earth and we want to study effect of celestial bodies on human beings, we study the motion of celestial bodies with respect to earth i.e. we take earth in centre and measure position of bodies around it, including. Sun, Moon and other planets. To measure the position we take far placed stars as fixed and use them to know the coordinates/position of the other celestial bodies. In astrology we define a planet as any celestial body revolving round the earth; thus Sun & Moon are considered as planets for the purpose of astrology.
The names of different planets according to the Indian and western system and their symbols are as under:
| Ravi or Surya || Sun ||☉|
| Chandra || Moon || ☽|
| Mangal or Kuja || Mars || ♂|
| Budha || Mercury || ☿|
| Guru || Jupiter || ♃|
| Shukra || Venus || ♀|
| Shani ||Saturn || ♄|
| Rahu || Dragon's Head ||☊|
| Ketu || Dragon's Tail || ☋|
| Indra || Uranus || ♅|
| Varuni ||Neptune || ♆|
| Vayu || Pluto || ♇|
On account of motion of Earth around the Sun, the Sun appears to move round the stars once in a year. The line along which the Sun moves is called the Ecliptic. The broad band or belt in the heaven extending 9° on either side of the Ecliptic is known as Zodiac. The Ecliptic passes through centre of zodiac longitudinally. The zodiac revolves once in a day on its axis from east to west.
The zodiac is divided into twelve equal parts, for purpose of astrology, called signs, which are named after the imaginary figures which the stars form in each division. Since zodiac consists of 360°, each sign will consist of 360°/12=30°. The signs are known as Rashis.
The twelve signs of Zodiac both in the Indian and western system and their symbols are as under: -
| 1|| Mesha|| Aries|| ♈|
|2 || Vrishabha || Taurus || ♉ |
| 3|| Mithuna || Gemini ||♊ |
| 4 || Kark || Cancer || ♋ |
| 5 || Simha || Leo || ♌ |
| 6 || Kanya || Virgo || ♍ |
| 7 || Tula || Libra || ♎ |
| 8 ||Vrishchik || Scorpio || ♏ |
| 9 || Dhanu || Sagittarius || ♐ |
| 10 || Makar || Capricorn || ♑ |
| 11 || Kumbha || Aquarius || ♒ |
| 12 ||Meena || Pisces || ♓ |
If Zodiac is divided into 27 equal parts then each part will be of 360°/27= 13°20'.
These 27 parts are known as constellations and each constellation measures 13°20' of arc of zodiac. Each constellation is further divided into four equal parts known as padas. Each Pada will measure 3°20'. Each Rasi, therefore, contains 2 ¼ constellations or 9 Padas.
The names of 27 constellations with their longitudinal span in zodiac are as under:
||Span in the zodiac
| 3||Krittika||26° 40'-40°|
| 4||Rohini||40°- 53°20'|
| 12||Uttara-Phalguni ||146°40'-160°|