An agricultural Chain epicyclic gear teach (also called planetary gear) contains two gears mounted so that the centre of one equipment revolves around the centre of the other. A carrier connects the centres of both gears and rotates to carry one gear, called the planet gear or world pinion, around the additional, called sunlight gear or sun wheel. The earth and sunlight gears mesh to ensure that their pitch circles roll without slip. A point on the pitch circle of the planet equipment traces an epicycloid curve. In this simplified case, sunlight gear is fixed and the planetary gear(s) 
roll around sunlight gear.
An epicyclic gear train can be assembled so the planet equipment rolls on the inside of the pitch circle of a fixed, outer gear band, or ring gear, sometimes named an annular equipment. In this instance, the curve traced by a spot on the pitch circle of the planet is a hypocycloid.
The combination of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train.[1][2] In cases like this, the ring gear is usually fixed and sunlight gear is driven.
Epicyclic gears obtain name from their earliest program, that was the modelling of the actions of the planets in the heavens. Believing the planets, as everything in the heavens, to be perfect, they could only travel in ideal circles, but their motions as viewed from Earth cannot end up being reconciled with circular motion. At around 500 BC, the Greeks developed the thought of epicycles, of circles travelling on the circular orbits. With this theory Claudius Ptolemy in the Almagest in 148 AD was able to predict planetary orbital paths. The Antikythera System, circa 80 BC, experienced gearing which was able to approximate the moon’s elliptical route through the heavens, and even to correct for the nine-season precession of that path.[3] (The Greeks could have seen it not as elliptical, but rather as epicyclic motion.)