Summary: This article examines the differences in the zodiacs use by Vedic Astrology and Western Astrology. It explains why Jyotish uses the fixed sidereal zodiac and not the movable tropical zodiac. It shows how sun signs, ascendants and all planetary positions can appear in different signs in the two systems.
Jyotish uses the fixed Sidereal Zodiac
- Jyotish astrology uses a different zodiac from that used in western astrology
- The zodiacs used in both Jyotish and Western Astrology are based on an imaginary sphere in the heavens. In both systems this is divided into 12 equal parts, each of 30 degrees, just like the segments in an orange. Both zodiacs use the same sign names e.g. Aries, Taurus, etc. for each of the segments. The sun takes about one month to apparently ‘move’ through each zodiac sign.
- Jyotish uses the fixed or sidereal zodiac. ‘Sidereal’ means ‘with respect to the stars’. So the starting point of the sidereal zodiac is permanently fixed in one position using the background of non-moving stars in our own galaxy as a reference point . So, in the sidereal zodiac, the sign divisions remain forever fixed against the background of the stellar constellations. So, the starting point of the first sign Aries is always fixed in Vedic Astrology.
- Western Astrology uses the movable, tropical zodiac. The starting point of this zodiac actually moves relative to the background of the ‘fixed’ stars over a period of time according to the position of the equinox. This movement is caused by the astronomically observable ‘precession of the equinox’ phenomenon .
- So, in Western astrology the position of what is known as the sign of ‘Aries’ actually moves through the sky against the background of the fixed stars. It is not linked to a particular stellar constellation at all! Many people, including students of Western Astrology, find this fact very, very surprising.
- The angular difference between the two zodiacs is known as the ‘ayanamsa’ and this figure increases with time . Although the starting point of both zodiacs coincided about 1700 years ago, the Western astrologer’s tropical zodiac has now moved away from this position.
- At this point in time (2018) there is a difference of about 24 degrees between the two zodiacs. Therefore, if our Sun is at 29 degrees Virgo in the Western tropical zodiac it will now be located at 29 – 24 deg. = 5 deg. Virgo in the sidereal zodiac. Notice, still in Virgo in this case in both Jyotish and Western astrology. However, if our sun lies between 0 deg. and 24 deg. in Virgo in the Western tropical zodiac it will now be in Leo in the sidereal zodiac used in Vedic astrology. It has moved backwards in the Vedic chart by the ayanamsa amount (about 24 degrees) and ends up in the previous sign . So, in this case our sun sign will now be different: Virgo in Western astrology, Leo in Jyotish! The same principle applies to all other planetary positions in our chart and to our ascendant too. This difference can explain many anomalies in charts interpreted by modern Western astrologers.
- Astronomers often criticise Western astrologers for using the movable tropical zodiac as the sign ‘Aries’ actually moves through the sky over a period of time. However, this objection cannot be levelled against Jyotish astrology as it uses a fixed and not a movable zodiac.
- Jyotish regards the stellar constellations or Nakshatras as being of considerable importance in chart interpretation, compatibility analysis and in determining the best time for important actions (Muhurtha). Hence it is hardly surprising that Jyotish uses a zodiac which is permanently anchored relative to the fixed stars.
 The ‘fixed stars’ are so far away from earth that their angular motion relative to our sun is extremely small, even over many thousands of years. So we can legitimately use the term ‘fixed’ or ‘immovable’.
 The equinox point on the Earth’s orbit around the sun moves, relative to the background of the ‘fixed’ stars, due to what is called the ‘precession of the equinox’. This is a well-defined astronomical phenomenon which is due to a slight ‘wobble’ on the Earth’s axis of spin (a bit like a spinning top whose axis itself slowly moves, tracing out a conical shape). It takes around 26,000 years for the earth to complete one precessional cycle.
 As of 2018 the angular difference between the two zodiacs is now about 24 degrees. This figure (or one very close to it), derived by Lahiri, is accepted by Jyotish astrologers. Most astrological tables show Lahiri’s ayanamsa. The tropical zodiac, therefore, moves relative to the sidereal (fixed) zodiac by about one degree every 71 years. (Although this movement seems small it was observed by ancient Egyptian astronomers thousands of years ago.) Over time it makes a big difference!
 The difference in planetary positions between the zodiacs is now around 24 degrees. If our sun was, say 14 degrees in Virgo in Western Astrology, it will be at 14 – 24 = – 10 degrees Virgo in the Vedic system! This simply means it has has moved backwards and changed sign into the position of 20 degrees in Leo in the Vedic system (as -10 + 30 = 20). However if our sun was at 28 degrees Virgo in the Tropical zodiacit will now be at 28 – 24 = 4 degrees Virgo in the sidereal zodiac. In this case it has not changed sign