If you are interested in learning basics of Indian Astrology then this is the article for you.
There are few terms which we will be learning in the course of this current material. Which are:
Zodiac and Celestial Zodiac
Sidereal Year & Tropical Year
Precession of Equinoxes
Graha’s (The Planets)
Rasi (The signs)
How to draw a simple Rasi chakra.
I due course, I will try to add few more to these.
Before we can go to understanding the Vedic Astrology, we have to first understand the terms realted to basic Astronomy and Astrology
We start with understanding the rotation adn reveloution of earth and the effect due to that. Earth rotates on its axis from West to East in 24 hrs approx and revolves around the Sun in 365 days approx. Due to the rotation of the earth on its axis Sun, Moon and other hevenly bodies seem to rise in the East and set in West. For a stationary person on Earth may think that Sun, Moon and other hevenly bodies are revolving around the earth, which is the Geocentric approch. So the general thinking is that the Sun , Moon and other planets move on the background of distant stars which dosent seem to move (relative to the Sun, Moon and other planets into consideration). To understand this let us take the concept of Celestial Sphere, Celestial sphere is an imaginary rotating sphere of "gigantic radius", concentric and coaxial with the Earth. All objects in the sky can be thought of as lying upon the sphere. Projected, from their corresponding geographic equivalents, are the celestial equator and the celestial poles.The celestial sphere is divided by projecting the equator into space. This divides the sphere into the north celestial hemisphere and the south celestial hemisphere. Likewise, one can locate the Celestial Tropic of Cancer, Celestial Tropic of Capricorn, North Celestial Pole, and South Celestial Pole. The Sun, Moon and other planets seem to be moving on the background of this Celestial Sphere. Though in truth the Earth orbits the Sun, we feel stationary, which makes the Sun appear to go around the Earth once a year in the counterclockwise direction (from west to east, counter to its daily motion across the sky) along a steady path called the ecliptc. If we consider that Sun is moving on this path called Ecliptc over this Celestial Sphere in 365 (actually 365.242.. ) days. So in 365 days Sun is completing 360° around the Earth, which means Sun moves to the east at the slow pace of only a bit under a degree per day. At the same time it is constantly moving (rather, appearing to move) from east to west as a result of the Earth's rotation. An sidereal day is the time it takes for the Earth to turn 360 degrees in its rotation; more precisely, is the time it takes a typical star to make two successive upper meridian transits. This makes the siderial day of 23h 56m 4.09s . In contrast Solar day is based on the idea that when the sun reaches its highest point in the sky, it is noon, wich take 24h. Siderial Day describes the rotation with respect to the cosmic background of the stars. In contrast to this, the rotation with respect to the Sun is 24 hours, differing because the Earth revolves around the sun once per year (or as Sun covers less then 1° per day). Per day the difference is
86 400 s / 365.25 = 236 seconds = 3 m 56 s
So around 4 mins is the difference beteween the Siderail day and a Solar day. Same way The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. For Example if we consider the start or 0° of the suns reveloution aroing the Excliptic as Aerise, when the Sun again comes back to Arise 0° it has compelted 360° which is what the Siderial year is. The sidereal year is 20 minutes and 24 seconds longer than the tropical year or One sidereal year is roughly equal to 1 + 1/26000 or 1.000039 tropical years. The difference is caused by the precession of the equinoxes. To undetrstand precession of the equinoxes and a tropical year consider this figure below. As we know Earth is rotaing on a axis which is tilted at an angle of 23.5° . Equinox is the event when the Sun can be observed to be directly above the equator. Tropic of Cancer and Tropic of Capricorn are the lins on Earth parallel to the equator whcih are the maximum or minumum limits of the Sun where it can be directly over the head at noon. When it's winter solstice in the Northern Hemisphere, the sun is directly overhead at noon only along the Tropic of Capricorn, and When it's winter solstice in the Northern Hemisphere, the sun is directly overhead at noon only along the Tropic of Cancer. Consider Figure 1, you can see a small white dot circeled with a red circle. whcih is the North Pole. In the figure, the figure of the earth when the earth is tilted away from the Sun (Winter Solstic) the Southereen hemishpere will be nearer to the Sun and will be having summer there. And the Tropic of Capricorn will be the place where the sun will be most near, or the max south where the Sun will be directly over head which will be on Dec 21/22 . When the earth moves on, the position which has Sun direct overhead comes nearer to the Equator until March 20/21 when it coincides the equator which is called the Vernal Equinox. That is when the length of the day and night are equal. AS the earth further moves the Northeren hemishpere will have Summer and the Tropic of Cancer will be the line which is the max where in the sun can be directly overhead. The Sun reaches this poin on Jun21/22, till this point Sun kept moving towrds North as the days passed. But form this point the Sun will traverse back to Equator. The time taken by the Earth to go from Winter Solstic and back to it that is via Vernal Equinox, Summer Solstic and Autumanal Equinox back to Winter Solstic is called One (1) Solar year or Tropical Year. Precession of the equinoxes is the slow revolving of the asis of the earth. Currently, this annual motion is about 50.3 seconds of arc per year or 1 degree every 71.6 years. The process is slow, but cumulative. A complete precession cycle covers a period of approximately 25,765 years, the so called great Platonic year, during which time the equinox regresses a full 360° (See Figure 2).
Figure 1 Figure 2
As a consequence of the precession is a changing of the pole star. Due to this precession of the equinoxes, during the end of the Solar year the Sun reaches Winter Solstic a bit early. Which is the why there is a difference between the sidereal year and tropical year and siderial year is 20 minutes and 24 seconds longer than the tropical year.
Even though the Sun,Moon and other planets move cross the celestial sphere, they do not wander all over it but are confined to a narrow strip, this strip is called ecliptic. Ecliptic is about 9 on both sides of the celestial Equator. In the figure below, The big sphere around the earth is called the Celestial Sphere, which is tilted twords the right side (in the figure). The space between the celestial equator and the Horizon can be called as Ecliptic
This Ecliptic is divided into 27 Nakshatras and 12 Rasis(Zodiac)
This Ecliptic is divided into 27 Nakshatras, identified by the prominent star(s) in them, that the Moon passes through during its monthly cycle. The starting point for this division is the point on the ecliptic directly opposite to the star Spica called Chitrā in Sanskrit. (Other slightly-different definitions exist.) It is called Meshādi or the "start of Aries". The ecliptic is divided into the nakshatras eastwards starting from this point. As there are 27 divisions of Ecliptic (360°) each nakshatras cover 13°20’ of the ecliptic.
Each of these 27 Nakshatras are further divided into 4 padas of 3°20’. Hence there are a total of 27x4 = 108 padas.
We have another division of this Ecliptic, ecliptic is also divided into 12 Rashi, each of 30°. The 12 Rashi's are:
|Number||Sanskrit Name||Western Name|
Each of these 12 rashi's has 9 padas.
Now we have the Grahas or the planets.The Grahas here has to be taken as the hevenly bodies that affect Earth through their gravity. Hence The extra-saturnine planets (Uranus, Neptune and Pluto) are not included in the category of Grahas. The 9 Grahas are
1. Surya (Sun)
2. Chandra (Moon)
3. Mangala or Angaraka or Kuja (Mars)
4. Budha (Mercury)
5. Guru or Brihaspati (Jupiter)
6. Sukra (Venus)
7. Shani (Saturn)
All the Ghras are self explanatory except for the last two Rahu and Ketu. Both these are misintrepreted as demons who eat up Sun and Moon causing eclipses. Inreality both of these are Nodes. Rahu is the ascending lunar node where as Ketu is the decending lunar node. As the moon is revolving the earth, the plane of the moon's reveloution cuts the plane of the ecliptic. The point where the moon is cutting the ecliptic while comming from below the ecliptic is called Rahu and the other point is called Ketu.
The position of the graha on the ecliptic is represented by Rashi, nakshatras and padas in that order. For example if we want to get the position of Sun on the Ecliptic, then its will be represented as :
Sun is in x rashi, in y naksharatam and in z padam. We can also know the any of the other two if either the degrees the Graha has traversed in nakshataram or the rashi.
With this information we can tell which Nakshataram is in which Rashi a particular graha is as follows.
As each rashi has 9 padas adn each nakshatram has 4 padas, starting with Mesha rashi we count 9 padas taking 4 padas of Ashvinī , 4 padas of Bharanī and 1 padam of Krittikā. So if a graha is in 3 padam of Ashvinī means it is in Mesha rashi, in the same way if a graha has traversed 21° in Mesha rashi, then we can tell in which padam of which nakshataram the graha is in. As the graha has traversed 21° in Mesha rashi, and Mesha rashi starts with Ashvinī nakshataram as each nakshataram is of 13°20’ on the ecliptic obvisely the gratha has crossed Ashvinī nakshataram but nas not completly crossed the next Bharanī nakshataram as Bharanī nakshataram would end at 26°40’ whcih is more then 21°. So the graha is in Bharanī nakshataram, now Bharanī nakshataram has 4 padas each of 3°20’, then the position of the graha would be in 13°20’ + 3°20’ + 3°20’ + 1. Whcih means the graha has completey crossed 2 padas in Bharanī nakshataram and is currently in the 3 padam. So the position of the graha would be "The Sun is in Mesha rashi and 3rd Padam of Bharanī nakshataram".