Horoscopes are the main output of astrology, the discipline which maintains that one's personality and destiny are guided by the locations of the planets as seen from the Earth. An astrologer, when given a subject's birth date, location, and credit card number, uses an impressive series of calculations and charts to figure a horoscope. Many are quite detailed, although most sceptics claim that a person could be just as accurate by making a few educated guesses.
Brief, one-line horoscopes may be found in newspapers. These are not unlike the messages found within fortune cookies - short, vauge, and largely unhelpful. Whereas a fortune cookie may be picked entirely at random from a jar, horoscopes are keyed to the date and location of one's birth and are thus supposed to be more specific to the individual. In order to prevent requiring the newspaper to print the daily horoscope for each and every individual on the planet, astrologers lump everyone into one of twelve categories, or 'signs', roughly according to the month of their birth. One then may hasten to conclude that a horoscope is thus twelve times more individually tailored to your needs than is a fortune cookie. However, it pays for the horoscope-writer to overgeneralize, because it is clear that, for instance, should you happen to die today, an entire twelfth of the population will not die with you. Some glossing over of the minor details is necessary.
Because horoscopes are derived from the relative positions of the planets and stars as visible from Earth, outsiders would find little use for them. It has aparrently never occurred to Earth-centric astrologers to consider constructing a horoscope for someone born on a neighboring planet or star system. If you are in fact from another planet it may still be possible, using careful triangulation through relativistic space-time geometry, to calculate the positions of the planets in the Sol system at the time of your birth, and so find your 'sign.' If at this point you don't like your horoscope much, you can always try a different newspaper.