Astrology is a science, and like Astronomy, it studies the stars, planets, constellations and celestial bodies spread across the sky; only the ways and purposes of the studies are different.
Astrology has a very interesting way of organising the whole cosmos into the factor of 12. Let’s see how.
Every planet or star has an orbit and the sky of each planet has a full measure of 360 degrees. Like a clock, it is divided into 12 equal measures of 30 degrees each. Each such part is called a Rashi or sign. Each such Rashihas a constellation, which can be easily seen in the night sky. That part is given the name of that particular constellation.
The moon’s transit through these constellations make 12 months of the vedic calendar. This cycle of a month starts with the day after Amavasya, that is the new-moon day, with Pournima, the full moon day as end of the fortnight and ends with Amavasya. For reference, the months of Gregorian calendar are based on the solar movement.
Now the vedic chart is also designed with 12 ‘Sthaan’ or Houses. These houses are again the 30 degree equal parts of the whole 360 degrees. Each sthaan has its own peculiarities and characteristics.
There is another group of 12 celestial bodies – planets, sun, moon and the North node –Rahu or the South node –Ketu,
Each Rashi and Sthaan is ruled by one of these bodies; either a planet, or Sun, Moon, Rahu or Ketu.
You will see that we have 3 groups of 12 – Rashi, Sthaan, and their rulers. As you can imagine, there are umpteen permutations and combinations of these. Each individual has her own unique combination of these Rashi, Sthaan and ruler. Each chart is an unique as the individual, making the whole study very complex and personalised.