Equal house system (Hindu astrology)

The Sign-wise Equal house division of the Zodiac or Rasi-chakra is a very old system of house division; in this system all houses are of equal length. Unlike the Western astrology that measures the longitude of a house from the exact ascendant-point in the sign rising in the east treated as its cusp, in Hindu astrology the entire sign is treated as a house irrespective of the ascendant-point in the sign rising in the east. The standard Hindu convention is to treat the house and the sign of equal length. It considers the twelve houses in the fixed Rasi-chakra (Zodiac), and is practically an "Equal-sign Equal house system". Hindu astrology is sidereal astrology , in which system planetary movements are tracked against the fixed position of the stars or nakshatras; it is believed to give a more accurate astronomical representation of the Sun’s position in relation to the skies i.e. the Zodiac, using the Ayanamsa (amount of precession), and incorporates star-signs based on the movement of the Moon.

The Vedic Rishis were aware of the Zodiac (Rig Veda I.164.48) which awareness echoes in the Atharvaveda (Mantra X.viii.4) as :-

the Rishi speaks about the wheel of twelve spokes, which has three navels with three hundred sixty nails. The spokes are the twelve Solar months or twelve Zodiacal signs or rasis, the three hundred sixty nails are the three hundred sixty degrees of the Zodiac, and the three navels are the three sets of Chaturmasas (Four months x three) that make up a year. The horoscopic picture (birth-chart) is the superimposition of the Space-divisions over the Elliptical orbit; the four vertical and horizontal lines (in the South Indian chart) that intercept the orbit lead to a four-fold division of space in two dimensions leading to a periphery of twelve columns or houses and a near quandrular demarcation that depicts a two-fold division. This picture is evident from Parasara’s description of the Kala Chakra and Jaimini’s Rasi aspects. The mathematical features of the sequence of peripheral divisions through the three-fold, four-fold and five-fold divisions; the superimposition of these space-divisions onto a curvilinear path yields the divisions 4, 8, 12, 16, 20, 24, 28…., or 4(n-1) division of the periphery for an n-fold division of space – n=(1+3 I). The nakshatra-divisions of the Zodiac are only twenty-seven in number and the real mathematical process was a division of the ecliptic into one hundred eight parts of three degrees twenty minutes each (equal to one navamsa or 1/9th division of a sign) which fact is corroborated by Maitrayaniya Upanishad (VI.14) which tells us that – "Time beginning with the moment to the twelve-fold-natured-year is the form the Sun bears. Half of the year belongs to fire and half belongs to water. From the beginning of Makha (120 degrees) to the middle of Sravista (300 degrees) belongs to fire (Agni)(clockwise). Step by step from the end of Sarpa (120 degrees) to the middle of Sravista belongs to water (300 degrees – anticlockwise). Then by subtlety are the single parts of time, the navamsas, together with the moving ones (the planets), by this measure time (the year) is measured."

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Wikipedia