What was the Michelson–Morley experiment, and what did it prove?

The 1887 Michelson–Morley experiment sought to detect Earth’s motion through the ether by comparing light beams in perpendicular directions. The result showed no variation, implying a stationary Earth. Instead of accepting this, scientists claimed the measuring device itself contracted slightly, nullifying the result. Sungenis said this was a contrived explanation designed to protect heliocentrism.