Satellite laser ranging

Satellite laser ranging is a way of measuring the distance between a satellite and the Earth. It uses lasers, which are flashes of bright light. The laser on the satellite sends a bright flash of light down to Earth. A special telescope that can detect the laser's light is pointed at the satellite. When the light reaches the telescope, it measures exactly how long it took to get there. By using this information, scientists can calculate how far away the satellite is from the Earth.