All 52 chapters
  1. Part 1 · The sky and the chart
  2. The sky above us
  3. Time and place of birth
  4. Two zodiacs
  5. How a chart is drawn
  6. Part 2 · The building blocks
  7. The 9 planets
  8. The 12 signs
  9. The 27 nakshatras
  10. The 12 houses
  11. The lagnas
  12. Part 3 · How planets work together
  13. How planets interact
  14. Friends, dispositors, exchanges
  15. House lords
  16. Reading one placement
  17. Part 4 · Strength and condition
  18. Dignity in depth
  19. A planet's mood
  20. Planetary strength
  21. Ashtakavarga in depth
  22. Part 5 · Patterns: yogas and doshas
  23. Yogas
  24. Doshas
  25. Part 6 · The nakshatras up close
  26. Reading a nakshatra
  27. Tara Bala
  28. Part 7 · Divisional charts
  29. Divisional charts
  30. Navamsa in depth
  31. Part 8 · Timing
  32. Dashas
  33. Transits
  34. The annual chart (Tajika)
  35. Part 9 · Relationships
  36. Compatibility
  37. Marriage in depth
  38. Part 10 · Advanced systems
  39. Special points
  40. Jaimini astrology
  41. Arudha padas
  42. KP astrology
  43. Nadi astrology
  44. Part 11 · Choosing the moment
  45. Panchanga
  46. Muhurta
  47. Prashna (horary)
  48. Part 12 · Life areas
  49. Career, money and business
  50. Travel, abroad, spirituality
  51. Health and longevity
  52. Karma and past lives
  53. Remedies
  54. Rectifying a birth time
  55. Part 13 · Western astrology
  56. Western astrology basics
  57. Aspects and chart shapes
  58. Western prediction
  59. Synastry
  60. Horary and electional
  61. Part 14 · The wider world
  62. Mundane astrology and eclipses
  63. Astrocartography and branches
  64. Part 15 · Putting it all together
  65. How it all fits
  66. How AstroMatch4u scores a chart
  67. Using astrology well
Part 1The sky and the chart
CHAPTER 3

Two zodiacs: tropical and sidereal

Why is my Vedic sign different from my newspaper sign?

Both systems cut the same band of sky into twelve 30° signs. They disagree only on where to start counting.

Tropical zodiacUsed in Western astrology. 0° Aries is fixed to the spring equinox, so the signs follow the seasons. Sometimes called the "moving" zodiac, because it slowly slides against the stars.
Sidereal zodiacUsed in Vedic astrology. 0° Aries is fixed to the stars themselves, so the signs match the constellations. Sometimes called the "fixed" zodiac.

Precession: why they drift apart

The Earth wobbles slowly on its axis like a spinning top, one full wobble every 25,800 years or so. Because of it, the spring equinox slides backwards against the stars by about 1° every 72 years. This is the precession of the equinoxes. Around 1,700 years ago the two zodiacs lined up; today they are about 24° apart, which is why most people's Vedic Sun sign is one sign earlier than their Western one.

two people walking round a track who started together. One walks very slightly slower, and every lap the gap grows by a step.

Ayanamsha: the size of the gap

The gap between the two zodiacs is the ayanamsha. Everyone agrees it exists, but not on its exact size, because each school picks a different star as the anchor:

AyanamshaAnchored toCompared with LahiriUsed by
Lahiri (Chitrapaksha)The star Chitra (Spica) at 0° Libra—Government of India calendar; most Vedic astrologers
RamanB. V. Raman's calculationAbout 1½° smallerFollowers of B. V. Raman
KP (Krishnamurti)K. S. Krishnamurti's calculationA few minutes of arc smallerKP astrology
Fagan–BradleyWestern sidereal researchA little under 1° largerWestern sidereal astrologers

A different ayanamsha moves every planet by the same small amount. It only changes a reading when a planet or the ascendant sits close to the edge of a sign or nakshatra.

Ephemeris and planetary longitude

An ephemeris lists each planet's longitude for every day. Modern software computes it from orbital models instead of printed tables. A sidereal position is simply the tropical one minus the ayanamsha: Sun at 10° tropical Leo, minus 24°, is 16° sidereal Cancer.

charts use the sidereal zodiac with the Lahiri (Chitrapaksha) ayanamsha.

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