* Astronomy

The Hill sphere is the region of space where an astronomical object's gravity is the dominant force affecting nearby objects. Earth's Hill sphere extends to about 1.5 million kilometres, 0.01 AU or 932,000 miles, from the planet.

In more precise terms, the Hill sphere approximates the gravitational sphere of influence of a smaller body in the face of perturbations from a more massive body. It was defined by the American astronomer George William Hill, based upon the work of the French astronomer Édouard Roche. For this reason, it is also known as the Roche sphere.
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