Earth's oblateness refers to the slight flattening of the planet at the poles and bulging at the equator. This shape is caused by Earth's rotation, which creates a centrifugal force that pushes outward at the equator. As a result, the equatorial diameter is about 43 kilometers (27 miles) larger than the polar diameter. This phenomenon is a key factor in understanding Earth's gravitational field and its effects on satellite orbits. The oblateness is quantified by a parameter known as J2, which measures the deviation from a perfect sphere. This information is crucial for accurate navigation and satellite positioning systems like GPS.