Zodiac celestial coordinate system, or more specifically an ecliptic coordinate system, which takes the ecliptic as the origin of latitude and the Sun's position at vernal equinox as the origin of longitude. The English word ' derives from ', the Latinized form of the Ancient Greek "zōidiakòs kýklos" (), meaning "cycle or circle of little animals". "Zōidion" () is the diminutive of "zōion" (, "animal"). The name reflects the prominence of animals (and mythological hybrids) among the twelve signs. The zodiac was in use by the Roman era, based on concepts inherited by Hellenistic astronomy from Babylonian astronomy of the Chaldean
Ancient Greek astronomy Perga (c. 262 BC–c. 190 BC) responded by introducing two new mechanisms that allowed a planet to vary its distance and speed: the eccentric deferent and the deferent and epicycle. The deferent is a circle carrying the planet around the Earth. (The word "deferent" comes from the Greek fero φέρω "to carry"and Latin "ferro, ferre", meaning "to carry.") An eccentric deferent is slightly off-center from Earth. In a deferent and epicycle model, the deferent carries a small circle, the epicycle, which carries the planet. The deferent-and-epicycle model can mimic the eccentric model, as shown by Apollonius' theorem. It can also