Significance
The sun sign is important to an astrologer for what it says about a person's general personality. Unlike the moon sign, which changes every three days, the sun stays in one sign for an entire month. This makes it the easiest part of the chart to determine. Along with the Ascendant and the moon sign, the sun sign helps to explain why a person reacts to life's challenges the way she does.
Elements
Each of the twelve sun signs represents one of four elements: earth, air, fire and water. Aries, Sagittarius and Leo sun signs share fire characteristics, including passion, ambition and confidence. They can be aggressive and impulsive. Cancer, Pisces and Scorpio are water signs, very emotionally-charged individuals who are intuitive and nurturing. Air signs include Libra, Gemini and Aquarius. They are good communicators, and are known for coming up with the best ideas; they are often accused of thinking too much. Taurus, Virgo and Capricorn are earth signs. They are practical and responsible, and somewhat stubborn.
Qualities
Sun signs can be further classified by "qualities," ways that different signs face the world. These qualities are cardinal, fixed and mutable. Cardinal signs such as Aries, Cancer, Libra, and Capricorn are best when in charge. They are usually outgoing and confident of their abilities. The fixed signs of Leo, Scorpio, Aquarius and Taurus are stubborn, "fixed" in their ways; they work steadily toward a goal and love the details. Finally, there are mutable signs; these folks adapt to situations very easily and are restless spirits, involving themselves always in one too many projects. Mutable signs are Gemini, Virgo, Sagittarius and Pisces.
Numerical
Sun signs have numerical counterparts that provide their own characteristics. Aries is the first sign and Pisces the 12th. Aries folks are independent and self-involved, traits that go along with the number one. Each sign progresses from the one before it, with Aries very individually motivated, Libras balanced between internal and outward existence, and Pisces the humanitarians of the zodiacs, concerned only with others.
Planetary
Each sign of the zodiac is ruled by a planet; therefore, the planets play a large role in the characteristics of the sun signs. Mars rules Aries, adding aggression and overconfidence. Venus rules Taurus and Libra, two signs that love the beautiful things in life and who always strive for harmony. Mercury lends its strength in communicating to Gemini and Virgo. The moon, which is known for its connection to emotions and family, rules Cancer, a sign known for its nurturing attitude.The sun rules Leo, giving these people an outgoing and sunny disposition. Jupiter rules Pisces and Sagittarius. These folks are deep thinkers, interested in education and anything that expands the mind. Saturn is in charge of Capricorn, adding maturity and wisdom to the sun sign. The dreamy, rebellious Neptune commands Aquarius, and Pluto, the planet of transformation and rebuilding, rules Scorpio.
Cusps
Most people will find that one sun sign describes them appropriately. But a select few who are born between the 20th and the 22nd of the month may find that they must pick between two different sun signs. People born during the time that the sun moves from one sign to the next are known as "cusp babies." A quick check with an ephemeris and knowledge of a person's exact birth time can determine a person's technical birth sign, but he may still find that some traits from the next sign fit his personality as well.