Astro*Dictionary by Michael Erlewine

4 articles for "Adjusted Calculation Date"

Used in Secondary Progressions. Since secondary progressions use a day in the ephemeris to represent a year in an individual's life, the planetary positions in the ephemeris corresponding to the progressed year must be correct for some day and time in the progressed life of the individual. That day and time is the adjusted calculation date. The ACD simplifies interpolation by assigning a date, the same from one year to the next, for which the progressed planets have positions as listed for noon in the ephemeris for the day corresponding to the progressed year. There can be an adjusted calculation date for noon or midnight.

♦ Secondary Progressions

Based on the date and time of birth, the adjusted calculation date is the date for which the planetary information on the progressed date is activated for the progressed year. A chart cast for the day corresponding to the progressed year using the birthtime represents a year of progressed planetary influence beginning at the adjusted calculation date. If the ACD is January 4, the the progressed positions as taken from the ephemeris for any given year correspond to January 4th of that year (not to the birthday). To determine the progressed positions for any other time in the year, the difference between the adjusted calculation date and the birthday is converted into percentage of daily planetary travel using a day-for-a-year ration of progression. Noon and midnight ephemerides produce adjusted calculation dates one half a year apart, since half a day corresponds to half a year.

Example calculation:
Take a birthtime of 7:21 PM GMT on June 25, 1959 and a noon ephemeris (standardized time such as EST must be converted to GMT for use with an ephemeris set for GMT). Seven hours and 21 minutes after noon is the same as 441 minutes, which is .30625 of one day (1440 minutes). Multiply this by the number of days in a year to determine the corresponding number of days the adjusted calculation date occurs before the birth date (for birthtimes after noon, the adjusted calculation date occurs before the birth date; for birth times before noon, it occurs after the birth date). In this case, .30625 of 365 days is (rounded) 112 days. June 25 is the 176th day of the year (1959 was not a leap year). The adjusted calculation date is then 176 - 112 or 64, which is March 5. (A "days between two dates" table is handy for this work.) The March 5th adjusted calculation date would be used as follows. The positions of the planets listed for July 19, 1959 correspond to March 5, 1983, the beginning of the progressed 24th year. The calculations using a midnight ephemeris are similar only the percentage of a day is determined between the birthtime and midnight rather than the birthtime and noon.

♦ Secondary Progressions

A calendar date during the year whichsimplies one's work when using the method of Secondary Progressions. The ACD is that date when the planetary information on any line of an Ephemeris that one is using becomes activated by the progression. There are two ACD'S: one for Noon and one for Midnight Ephemerides.