Movement of Sun through Zodiacs — Tropical zodiac, Sidereal zodiac and Ayanamsa from Vedic Astrology
A friend of mine asked me an interesting question on how they used to see the Leo zodiac sign right above their head some few years back at that time of the year and it is no longer the same. I was intrigued by those thoughts and started seeking an answer for the same. When I intensely focus on a topic and sleep with those questions in my mind, I have seen the answer comes to me the next day or in the next couple of days either directly as flashing cue words or through related discussions. A similar thing happened in this seeking too and made me feel extremely grateful too.
To understand how the Sun is seen to move through zodiacs in the perspective of Vedic astrology, we consider a common man’s point of view where he/she does not realize that it is the Earth that is moving but the Sun is rising in the east and setting in the west. So with this mindset let us understand the movement of Sun through the Zodiacs and how there is a variation in the starting of the Tropical year, Sidereal year and the concept Ayanamsa and there is a very minor variation in the position of sun getting aligned with these zodiacs every year.
From Earth, the sun moves around the Earth in the celestial sphere along the path called ecliptic and intersects with the celestial equator at two points namely Vernal Equinox and Autumnal Equinox. Equinox literally means “equal night”. On the vernal (spring) and autumnal (fall) equinoxes, day and night are nearly the same length (the date on which day and night are actually closest to the same length is called the equilux, and occurs a few days towards the winter “side” of each equinox). Neither hemisphere gets more sunlight than the other, so both have similar seasons (fall in one hemisphere and spring in the other).
Tropical Zodiac:
The vernal equinox is also called the March equinox and the autumnal equinox is also called as September equinox. The western astrology considers the vernal equinox as the beginning of the tropical zodiac i.e, 0 degrees with ecliptic equator is observed on March 21st. We have to remember this just considers the movement of Sun from one equinox to the next vernal equinox as the tropical year. The moment of the equinox has a powerful metaphysical meaning: it is the moment of the ultimate balance between day and night, light and darkness.
Balance brings unity, unity brings infinity and the infinity is the origin of everything. Hence the Equinox became the origin of an annual cycle, an astronomical and astrological year. The Sun is assumed to be at zero degrees inclination with Aries zodiac at the time of equinox. While this was true in the year 285 A.D and not anymore, we will see the reason soon why it is not so now. But just visually speaking the Sun is seen on the boundary of pisces and aries and not exactly where it is expected to be. This gives the concept of another zodiac system. The sidereal.
Sidereal Zodiac:
This is an ecliptic band that extends 9 deg north of the ecliptic path and 9 deg south of the ecliptic path. In this zodiac band, the path of moon, stars and planets are also included.
The starting of the sidereal zodiac is derived with the help of a super star that is visible in the night , the Spica and the visible constellation bands accordingly. The diametrically opposite 180 degree from Spica lies the starting of Aries. Thus unlike the tropical year, the sidereal year is the movement of Sun from beginning from a point in zodiac to again back to that point (which happens on April 14). This year is slightly longer than the tropical year since, by the time Sun reaches the same declination again (as it was at the start of the year), the equinox has moved little backward due to the precision of equinox and thus Sun has to take little extra time to cover up the distance to the original point of start in the zodiac.
So let us see how the equinox moves backwards now and why the sidereal year is a more appropriate solar year.
Rotation , Revolution and Precession of equinox:
As we are aware, Earth has three types of motion with a rotation about its axis, revolution around the sun and the third movement being a wobble about its tilted axis similar to that of a top as a result of the gravitational pull from moon and sun. The technical term used to describe this wobble is precession of equinox.
The tilt of earth is itself changing its direction, tracing a circle on the celestial sphere. With this the alignment of the polestar with the earth’s axis is changing. This means that the point in which the equinox falls is itself changing. Astronomers found that the period in which the equinox is tracing the circle on the celestial sphere is some 26000 years (different views exists on this, but we are sticking to chitrapaksha system(now lahiri aynamsa system) used by varahamihira). So each year the equinox is preceding with a rate of some 49.86 seconds. Over years from the time when equinox actually fell at the beginning of Aries, the equinox has moved backwards to 7degree pisces.
Ayanamsa:
Mathematically, the difference between the Sidereal and the Tropical year can be seen as follows.
Sidereal Year = 365 days 6 hours 9 minutes (from one vernal equinox to the next)
Tropical Year = 365 days 5 hours 48 minutes. (from sun entering aries to the next time)
Difference = 20 minutes 24 seconds in one year, or 50 Arc-Second of circle per year.
This seems to be small, but over a period of time, it could add up a lot. It could be
1 Day in every 71 years
1 Degree in every 72 years
1 Month in every 2160 years
1 extra Year in 25772 years (between 25700 to 26000 years)
Considering 12 Zodiacs and 27 stars, it could be
1 zodiac in 2160 Years (25920/12)
1 star in 960 Years (25920/27)
This exact difference in degrees between the moving vernal equinox and the exact sidereal zero Aries point is called as Ayanamsa in Indian vedic astrology.
Ayanamsa is a compound word of ayana and amśa, meaning, degree or part of the movement where the movement is that of the sun in the backdrop of the stars.
There are different methods used to measure Ayanamsa, but we will use the Chitrapaksha/Lahiri ayanamsa used by Varahamihira. So is the solar year still starting from April 14th even now? Naturally no, owing to the wobble or precession movement we have seen above. Every 2160 years as seen above the sun will be in a new zodiac on April 14th. So according to Varahamihira, in the year 2445 A.D (2160–285),the year will not start with Aries on April 14th as in the year 285 A.D, the starting point of the Sidereal zodiac and Tropical Zodiac coincided. Who will rewrite this in 2445 A.D? My hunch is possibly we will have another Varahamihira come about and state so :-)
