While most people will know astrology from the checkout at the grocery store or the amusing little predictions at the back of the local section of the newspaper, it is one of the oldest forms of divination. Most are familiar with the Western zodiac and the Chinese zodiac, but there are several other systems from Asia, and also Vedic astrology from India. There are more recent zodiacs as well like the Celtic Tree Horoscope and at least two Native American ones.
Like Palmistry, there are several types of divination that fall under the broad term of astrology. Horoscopy is the practice of casting of astrological horoscopes. Genethlialogy studies the influence of the stars at birth.
There are various reasons to use astrology, but all of them have to do with predicting future events. These events may be of a personal nature or have a broader scope. Charts are calculated using the movements of the earth in relation to the other planets and the stars and their constellations. All these movements are reduced to mathematical equations used to explain the magnetic influences of planets near and far. At the time of birth, a natal chart predicts what the baby is likely to do with its life. Personal predictions later in life are made by comparing the natal chart to the current placement of planets. Without a natal chart, the predictions of the supermarket checkout line and the newspaper are really too general to be applied to individuals. A Natal chart allows people to know how likely they are to fall under one influence or another.
Astrology may be utilized to see whether an action is prudent (Emotional Astrology) or to predict the outcome of some event whose inception is known (Inception Astrology). So long as the location, date, and time frame are known (sporting events, trials, union), a chart may be drawn up to see its possible outcome. Astrology may be used to predict future natural events (Horary Astrology) such as earthquakes, tidal waves, etc (see also Astrometeorology or the actions of large groups of people or societies and their activities (Mundane Astrology).
Also, depending upon the sign you were born under, you will be more susceptable to certain disorders and illnesses than other people (Medical Astrology). Aries should look to their head and face for health problems, Taurus to the neck and throat. Gemini governs the arms, shoulders, and lungs. Cancer controls the breast and stomach. Leo wards the heart, back, and neck area. Virgo is in charge of the intestinal organs, while Libra controls the kidneys and lower back or spine. Scorpio reigns over the reproductive organs, and Sagittarius affects the hips and large muscles of the body. For Capricorn, it is the knees and shins that are most susceptable. Aquariuses should look to their legs and ankles, and Pisces have trouble with their feet, toes and mucous membranes. As a Pisces, I can say this is absolutely true. Fish were not meant to walk on their flippers or breath air.
Astrology is also called Roadomancy or Astromancy, a form of Aeromancy.