Astrology is the art and science of predicting certain events and patterns based on the observation of planetary movements and relationships and the study of how these movements and relationships affect terrestrial world events and the health, moods, relationships and personalities of individuals. Predictions are made by observing the relative positions of the moon, sun and planets in relation to one another and their perceived locations in the sky as observed from earth. It is important to note that while modern Astronomy calculates planetary position from the solar center of the Universe, Astrology uses the ancient geocentric model to make calculations. Once a single study, Western Astrology and Astronomy separated into two different disciplines in the 17th century CE.

Astrology was originally developed 3000 years BCE in various places throughout the world as a calendar system which allowed its practitioners to assist in the planning of important occasions as well as to predict weather patterns, seasonal changes, tides and important celestial events such as eclipses. In almost every culture that used it, it grew to become a part of religious, oracular, magical and medical traditions.

Western Astrology

Most known to the Western world, the Western system of astrology has its roots in ancient Greece and Persia and has grown and evolved over the years. Early astrologers observed countless fixed stars and 5 wandering stars (asteres planetai in ancient Greek) in the night sky. These wandering stars are now known as planets and the original five plus the sun and the moon are referred to as the classical planets. Modern scholars through the use of telescopes have swelled the number or planets to 9, though that number still varies. These wandering stars, as well as the celestial lights - the sun and the moon, change position in the sky in a predictable pattern, wandering through the 12 houses of the zodiac and the 12 Signs of the Zodiac. The 12 houses of the zodiac represent phases of life while the twelve signs of the zodiac each carry distinct qualities that impact the world when they are dominant. The relationship between the planets, that is, how they line up and the angles they form, as they pass through these signs and houses, further influences interpretation.

Ancient astrologers, and some modern astrologers, believe that the positions of the planets allowed them an glimpse into the minds of the Gods to better understand the Gods plans and wishes so best to please them and avoid their wrath. Most modern astrologers believe that the planets simply represent basic human drives, psychological impulses and archetypes.

Western Astrology in Magic(k)

Western astrology is often used by magical practitioners to determine the timing of their magical workings and spells. Usually, the location of the moon is what is looked at to make these determinations. Each sign of the zodiac is considered to be influential in certain areas of the human experience and this influence can add strength to a spell, or even mundane efforts toward associated goals. The moon in each sign adds its own influence, the new and waxing moon supporting work to increase or manifest while the waning moon supports work to decrease and banish. The full moon is considered by many to be most powerful and supporting of all magical efforts.

See the Planetary Correspondences, Zodiacal Correspondences and Spell Timing articles for more information.

Western Astrology in Religion

Many traditions associate the various planets with specific deities. Below is a chart of suggested associations.

The 12 signs of the Zodiac are also occasionally used by modern polytheistic Pagans to determine when the best time to focus on each of their Gods might be and when each God has the most influence. See http://www.hellenicgods.org/calenderhelleniczodiacal for more information on the Hellenic model.
Some people chose to begin the Zodiacal month when the sun enters the zodiac sign, usually around 21st of the Roman calendar month, while others choose to begin the month when the new moon occurs within the zodiac sign (usually within a few days of the sun entering the sign).

The following chart outlines these relationships.

Hindu Astrology

The planets in Hindu astrology are known as the Navagraha or 'nine realms'.

Chinese Astrology

In Chinese astrology the planets are associated with the life forces of yin and yang and the five elements, which play an important role in the Chinese form of geomancy known as Feng Shui. The Hindu and Chinese astrological traditions are mentioned here, but are discussed in greater detail in their own articles.