Ptolemy was an astrologer, mathematician ans astronomer. He is credited with being the first to correlate astrology and astronomy with his treatise commonly known as Tetrabibios. He was regarded as the leading astrologer of his time and Tetreabibios was actually the bible for astrologers for over a thousand years.
In modern western culture there are twelve astrological signs, most astrologers list Aries as the first sign. The signs are associated with constellations that are seen in the sky during the time periods that they represent. There are actually several interpretations of the zodiac at different times and for different reasons.
Tropical bases its interpretation on the vernal equinox of the northern hemisphere. Sidereal bases its interpretation on the appearance of the principal star in the constellation. The two systems dates however are not the same and are about month apart.
The signs are generally associated with the four elements : water, fire, earth and air. The Water signs are: Cancer, Scorpio and Pisces, the Fire Signs are Aries, Leo and Sagittarius, the Earth Signs are Taurus, Virgo and Capricorn, and the Air signs are Gemini, Libra and Aquarius.
In more Modern times a horoscope is often used to help guide the lives of people who feel that the stars are what make for a happier life and can be found in most any form of media from the local newspaper to your smartphone. You can check your horoscope and see what life has in store for you in the coming day, month or year. Most people who do check them try to check them daily.