Capricorn
Capricorn is the zodiac sign for people born between December 22 and January 19. Element: earth; modality: cardinal; ruling planet: Saturn. The cusp dates shift by a day from year to year, so if you were born near a cusp, check your sign with the calculator.
Personality
Capricorn is the sign of the long haul. Capricorns plan years ahead, are willing to wait for results and take responsibility where others dodge it.
Strengths: discipline, reliability, realism, the ability to keep their word and handle a heavy load.
Weaknesses: harshness toward themselves and others, difficulty expressing feelings, a tendency to measure relationships by efficiency. Capricorns rarely allow themselves to stop.
The Gemini man and woman
The Capricorn man is responsible, reserved and reliable; he says little about his feelings but doesn't walk away.
The Capricorn woman is driven and independent; she finds it hard to allow herself weakness even with someone close.
Career and money
Work that calls for structure and endurance suits them: management, finance, construction, law, civil service, science.
Capricorns plan their money better than anyone, save and invest for the long term. Their risk is working so much that there's no time left to spend it.
Compatibility
Traditionally, the easiest matches are signs of the same element and of compatible elements; for Capricorn these are Taurus, Virgo, Scorpio and Pisces.
The most challenging are signs in square and in adjacent positions: Aries, Libra, Sagittarius and Aquarius. The opposite sign is Cancer: strong attraction and an equally strong struggle.
These are general rules of aspects, not a verdict. Each pair is covered separately in zodiac compatibility.
The sign in the birth chart
Your Sun sign is just the position of the Sun at the moment of birth. A full birth chart also includes the sign of the Moon (emotions), the Ascendant (first impression) and the positions of the other planets.
That's why a person may "not seem like an Aries": they have an Aries Sun, a Cancer Moon and a Libra Ascendant, and what comes across is nothing like a Martian manner. Horoscopes in the media work only with the Sun sign, hence the feeling that they aren't about you.