The zodiac is divided into 12 signs, each 30 degrees long. The cycle of zodiac signs starts with Aries, which begins at the spot on the ecliptic where the Sun is on the first day of spring. These 30 degree sections of the sky are actually blocks of space, not time.

Zodiac signs are often confused in the popular mind with "sun signs". When a person says, "I'm an Aries!", what they're really saying is they were born at a time of the year when the Sun is in the zodiac sign of Aries. Because our calendar is designed to mimic the motions of the Sun around the zodiac, the Sun is in Aries at nearly the same time period each year (roughly March 20th or 21st to April 19th or 20th). Hence the 12 sun signs are like months of a calendar based on the zodiac. They represent time, not space.

The motions of the other planets through the zodiac signs can be quite irregular, compared to the Sun's motion. On average, they range from the fast moving Moon (which spends about 2-1/2 days in each sign) to the slow poke Pluto (roughly 12 to 24 years in each sign).