Natal Chart - Erecting The Natal Chart

Erecting The Natal Chart

Once the astrologer has ascertained the exact time and place of the subject's birth, the local standard time (adjusting for any daylight saving time or war time) is then converted into Greenwich Mean Time or Universal Time at that same instant. The astrologer then has to convert this into the local sidereal time at birth in order to be able to calculate the ascendant and midheaven. The astrologer will next consult a set of tables called an ephemeris, which lists the location of the sun, moon and planets for a particular year, date and sidereal time, with respect to the northern hemisphere vernal equinox or the fixed stars (depending on which astrological system is being used). The astrologer then adds or subtracts the difference between the longitude of Greenwich and the longitude of the place in question to determine the true local mean time (LMT) at the place of birth to show where planets would be visible above the horizon at the precise time and place in question. Planets hidden from view beneath the earth are also shown in the horoscope.

The horoscope is then divided into 12 sectors around the circle of the ecliptic, starting from the eastern horizon with the ascendant or rising sign. These 12 sectors are called the houses and numerous systems for calculating these divisions exist. Tables of houses have been published since the 19th Century to make this otherwise demanding task easier.