A sun gear is a central gear in a gear system, often found in mechanical devices like automatic transmissions and differential systems. It is called "sun" because it resembles the sun in a solar system, with other gears, known as planet gears, orbiting around it. The sun gear plays a crucial role in transmitting power and motion within these systems. In a typical gear arrangement, the sun gear is surrounded by multiple planet gears that rotate around it. These planet gears are mounted on a carrier, which can also rotate. This configuration allows for efficient torque transfer and speed reduction, making sun gears essential in various applications, including automobiles and industrial machinery.