The ongoing Lunar Laser Ranging Experiment measures the distance between the Earth and the Moon using laser ranging. Lasers on Earth are aimed at retroreflectors previously planted on the Moon and the time delay for the reflected light to return is determined. Since the speed of light is known with very high accuracy, the distance to the moon can be calculated. This distance has been measured with increasing accuracy for more than 35 years. Some of the findings of this long-term experiment are: