HOW TO CALCULATE THE PLANETS’ PosITIONS 51
minutes in each hour. Thus we obtain 5 hours 52 minutes, which we add to the true local time of birth, 23 minutes after 8 in the morning, and the sum is 15 minutes past 2 o’clock in the afternoon, which is the G. M. T.
That is to say, at the identical time when the child was born and the Chicago clocks pointed to 15 minutes after 8 o’clock in the morning, the Observatory clock at Greenwich showed 15 minutes past 2 o’clock in the afternoon.
This latter is the time we must use to make our calculations of the planets’ places, and in order to have as few factors in mind as possible the beginner is advised to forget the local time of birth when once he has found the G. M. T.
In Western longitudes: the G. M. T. may advance into the day following birth on account of the addition of 4 minutes for each degree of longitude. In the cases where the longitude of the birthplace is East of Greenwich a subtraction of 4 minutes is made for each degree; hence the G. M. T. may recede into the day preceding birth. Therefore we speak neither of birthday nor birth hour, but of G. M. T. day and hour.
Our concern is now to find the motion of the planets on the G. M. T. day, which is from the noon before G. M. T. to the noon after the G. M. T The positions of the planets are found in the ephemeris.