Dane Rudhyar presented the tropical zodiac primary factors,Rudhyar (1943) used in the curriculum of the RASA School of Astrology. The tropical zodiac is the zodiac of seasonal factors as opposed to the sidereal zodiac (constellation factors). The primary seasonal factors are based on the changing ratio of sunlight and darkness across the year. The first factor is whether the chosen time falls in the half of the year when daylight is increasing, or the half of the year when darkness is increasing. The second factor is whether the chosen time falls in the half of the year when there is more daylight than darkness, or the half when there is more darkness than daylight. The third factor is which of the four seasons the chosen time falls in, defined by the first two factors. Thus
