The word is of Greek derivation: astro star and logos to study. The study of the stars began when the ancients noticed that the cyclical placement of planet and groups of stars had noticeable effects on all of nature. So, the definition becomes : astrology is the study of the effect of the planets and stars on the planet Earth (geocentric).

What is the Zodiac ?
The zodiac is an imaginary belt through which most of the planets travel when the ancients observed them in the night sky. Within this belt are twelve constellations hence the twelve signs of the zodiac. The constellations were given names of animals (mostly) which they vaguely resembled.  The astrological signs borrow the names of the constellations but are based on the seasons of the year, beginning with Spring.

In the Spring when the Sun comes North and crosses the Equator, a new zodiac for the following twelve months begins with 0 degrees of Aries (30 degrees in each of the twelve signs = 360 degrees). This moment is called the Equinox (Vernal Equinox in the Northern hemisphere: Autumn Equinox in the Southern hemisphere). The date varies because of leap year but time is approximately March 21-22. The Sun enters a new sign of the Zodiac from the 19th to the 24th of the month. In order to know precisely when the Sun changes signs, it is necessary to consult an EPHEMERIS (plural Ephemerides) for the subject year…more on this in later lessons.