The planets’ places will be the same in every map. That is to say, whatever the planetary longitudes and declinations are in the Mundane map for Greenwich, they will be exactly the same for all parts of the world.
As two illustrations of this simple method of erecting the Mundane maps for different parts of the world, we will take the Sun’s ingress into Aries for March 21 st, 1911. This takes place at 5h. 54m. 30s. P.M. on that day at Greenwich. We will then compute the same ingresses for Washington, in West Longitude, and Calcutta, East Longitude. Washington is 77°4’ W., equal to 5h. 8m. 16s., and Calcutta is 88°24’E., equal to 5h. 53m. 56s.
On casting the map for Greenwich we find that the Right Ascension of the Meridian, commonly known as the Sidereal Time, is 5h. 47m. 1s., and with the Tables of Houses for the latitude of Greenwich, the figure is erected. The planets’ places are computed for the time of the Ingress. Now to erect the horoscope for Washington we must subtract from the Greenwich Sidereal Time the difference in time between the two places, viz., 5h 8m. 16s. as Washington is in West Long., and this gives 0h. 38m. 45s. This is the Sidereal Time at the moment of the Sun’s Ingress into Aries at Washington.
The latitude of Washington is 38° 55’ N., and with a Table of Houses for this degree we erect the figure of the heavens. The planets’ places will be taken from the map for Greenwich without any alteration.
To erect the same map for Calcutta we add the difference in time between that place and Greenwich, it being in East Longitude, and with the Sidereal Time thus found, and Table of Houses for the Latitude of the place, we erect the map in the usual way, taking the planets’ places from the Greenwich map as before. The Sidereal Time at Greenwich for the moment of Ingress is 5h. 47m. 1s., and to this we add 5h. 53m. 36s., the difference between Calcutta and Greenwich, and the result is 11h. 40m. 37s., and with a Table of Houses for 22° 33’ N. (the Latitude of Calcutta) we erect a map.
The following tabular figure shows the Sidereal Times, and cusps of the houses, for the three figures used, and the planetary longitudes thereat.