Western Astrology has fixed dates for each Zodiac Sign. Depending upon your birth dates, your Zodiac sign is decided. The Signs begin typically around 20th to 22nd of each month and uptil the same dates of the next month (eg. Cancer – 21st June to 22nd July; or, Sagittarius – 22nd November to 21st December). The reason these dates were selected is that the Sun changes over from one sign to the other during these dates. So a Zodiac sign of Cancer would really mean that the Sun is in Cancer during that particular month. In contrast, if you look at your horoscope chart drawn as per the Indian systems, in very many of the cases, you will find the Sun is in the preceding sign from your Western Zodiac sign (Eg. If you are a Cancerian as per the Western Zodiac dates, there is a good chance Sun is in Gemini as per the Indian Horoscope chart). You can notice this difference of ‘One Zodiac Sign’, if, by any chance you have your Indian horoscope already with you.
This difference of about one Zodiac Sign between the Indian & Western systems occurs mainly due to the way the calculations are done. The calculations are linked to a component called Ayanamsha (“Ayana” – North/South movement of the Sun + “Amsha” – a Part or a component)
The word “Ayana” refers to the lateral movement of the Sun along the horizon. For a period of six months Sun apparently shows a shift towards the North. This northward movement is called “Uttara-Ayana”, while a similar Southward movement is called “Dakshina-Ayana”. These north-south movements of the Sun gives rise to the various seasons in Earth & is caused due to the tilt in the earth’s axis of rotation. These Ayanas also gives rise to the Solstices (Long Days & Long Nights) and Equinoxes (Equal Day & Night Time).
The ancient Indian Astronomers and Astrologers observed that the earth’s rotation is not uniform but there is a slight wobble like that of a top. The wobble in the earth’s rotation is small, but its effects are a noticeable change in the occurrence of the Equinoxes and the Solstices over a large period of time. This wobble and the resulting shift in the dates of the Equinoxes was observed by the ancient Indian Astronomers & Astrologers. A calculation was made and was noticed that due to the wobble, the earth’s axis makes a circle, giving rise to a 360o rotation every 26000 years (also called as the ‘Great Year’). In other words, the axis makes a 1o arc every 72 years. Thus, due to this wobble, it would mean that even our Zodiac signs and constellations are shifting when viewed from Earth. A 1o shift every 72 years would mean the Zodiac sign has shifted by about 27o (Approx. One Zodiac Sign) in these last 2000 years (about the time when Indian astrology originated). This is why there is a difference of one sign between Indian and Western systems.
The shift in the Zodiac Sign gives rise to two different systems of Astrology:
1. Tropical Zodiac (‘Sayana’ in Sanskrit): Tropical Zodiac follows what is currently observed when seen from earth’s vantage point. This system does not take into account the shift in the Zodiac sign that we discussed. Western Astrology follows the Tropical Zodiac. Planets are in respective Zodiac Signs as seen from earth.
2. Sidereal Zodiac (‘Nirayana’ in Sanskrit): In contrast the Nirayana (Sidereal) systems make a calculation to correct the error for the shift in the Zodiac. The logic here is that, true planetary positions are to be taken devoid of the shift in order to make accurate predictions. The amount of the axial shift has to be subtracted to arrive at true planetary positions. This component that is to be subtracted is called “Ayanamsha”. The word represents, the component or part due which there is a shift in the “Ayana” or the apparent position of the Sun, giving rise to Equinoxes and Solstices.
Indian Astrology follows the Nirayana system, and thus always the Ayanamsha is subtracted to arrive at the planetary positions in a horoscope chart.
The Controversy:
Now, while the concept of the Ayanamsha is clear, the actual literary references are several years old. The concept of shifting Zodiac and the ayanamsha calculations, references etc. were formulated almost about 2000 years back. It is believed that at that point the Sayana and Nirayana systems would have actually coincided and started to drift apart as the years & centuries passed. The original books were written in classical Sanskrit and in the format of a ‘Shloka’ employing the grammatical writing patterns of those times. Meanwhile during the decade between the 10th and the 19th century, India was ruled by several foreign entities, resulting in a change in spoken & written languages, lost literatures etc.
Ancient literature points out that the ‘Nirayana’ starting point of the Zodiac should be exactly opposite the Nakshatra of ‘Chitra’ (Spica). Thus, the starting point, or 0o Zodiac should be in Aries, exactly opposite the Chitra Nakshatra. However, this interpretation has several controversies and has been challenged by multiple sources, mainly due to a lack of our complete understanding of Sanksrit and the codified ‘Shlokas’. Over a period of time, different regions in India have adopted different interpretations and thus have varying definitions and calculations of the Ayanamsha.
Thus, we have Chitrapaksha Ayanamsha, Raman Ayanamsha, Sri Yukteshwar Ayanamsha and several local Panchangas which give varying calculations. When India got our independence, the then Prime Minister, Pt. Jawaharlal Nehru appointed a committee under N.C. Lahiri to study the topic and bring about a common Panchanga that would be applicable across India. The idea was to bring about uniformity in the calculations, and whereby we can have common dates for Indian festivals, holidays etc. He brought forth the Lahiri Ayanamsha which is now officially used and employed across India.
The debate in Ayanamsha calculations however continue and we still have regional differences and local Panchangas that vary in calculations. Meanwhile, efforts also continue among leading Indian astrologers to bring a greater understanding of our ancient literature. Computers and softwares have helped also in calculations and arriving greater consensus and accuracy in the astrological science.