If you could observe the motion of the Sun against the stars for an entire year, it would appear to trace out a large circle in the sky that we call the "ecliptic". This circle also happens to be the plane of the Earth's orbit around the Sun. The zodiac is a thin band of the sky on either side of the ecliptic. The word "zodiac" literally means "circle of life", since most of the zodiac signs are animals or people.
What are Zodiac Signs?
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).
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The modern astrological signs are the simplified pictures of the signs used in the Hellenistic times.
These are the twelve animals the signs represent:
Aries (The Ram)
Taurus (The Bull)
Gemini (The Twins)
Cancer (The Crab)
Leo (The Lion)
Virgo (The Virgin)
Libra (The Scale)
Scorpio (The Scorpion)
Sagittarius (The Archer)
Capricorn (The Sea-goat)
Aquarius (The Water-bearer)
Pisces (The Fish)
Calculate Your Personal Western and Chinese Astrological Signs
Traditional Hindu astrology has a sidereal coordinate zodiac system with twelve signs. The names of the Hindu zodiacal signs, or rāśis, are similar to Graeco-Babylonian signs:
meṣa "ram" (Aries)
vṛṣabha "bull" (Taurus)
mithuna "a pair" (Gemini)
karka "crab" (Cancer)
siṃha "lion" (Leo)
kanyā "maiden" (Virgo)
tula, from tulā "balance" (Libra)
vrushchik "scorpion" (Scorpius), also kaurpi, loaned from the Greek
kārmuka, cāpa, dhanus "bow, arc", cāpin "armed with a bow" (Sagittarius)
eṇa, mṛga "antelope", also makara "sea-monster" (Capricornus)
kumbha "pitcher, water-pot" (Aquarius)
matsya "fish", also jhaṣa, timi, mīna after specific kinds of fish (Pisces)
This "Hindu zodiac" (adhvan, rāśi) thus has similarities to Greek zodiac. The Graeco-Babylonian system of twelve signs overlays the native Hindu system of nine grahas or planets.
Chinese astrology also has a system of twelve signs sometimes also referred to as "zodiac". This does not necessarily imply a common origin, since the number of twelve naturally suggests itself from the number of synodic months in a year; in other words, the extent of a zodiacal sign corresponds to the path covered by the Sun between two new moons.
Like its Western counterpart, the Chinese zodiac features animals. However, the Chinese zodiac associates each animal with both one month and one solar year. Thus the signs repeat themselves every twelve year cycle.
The animals of the Chinese Zodiac are:
rabbit (or hare)
sheep (or goat)
pig (or boar)
For a list of how these animals map to the months and years see Chinese astrology. There is also a Chinese lunar zodiac comprised of twenty-eight lunar "mansions", each corresponding to a Chinese constellation.