Thus, the casting of a horoscope that is, the methods by which the astrologers ascertained the relative position of the heavenly bodies at the time of a birth--was a simple but fairly exact procedure.

Its basis was the zodiac, or the path traced by the sun in his yearly course through certain constellations.

At the moment of the birth of a child, the first care of the astrologer was to note the particular part of the zodiac that appeared on the horizon.

The zodiac was then divided into "houses"-- that is, into twelve spaces--on a chart.
In these houses were inserted the places of the planets, sun, and moon, with reference to the zodiac.

When this chart was completed it made a fairly correct diagram of the heavens and the position of the heavenly bodies as they would appear to a person standing at the place of birth at a certain time.
Up to this point the process was a simple one of astronomy.