Special mirrors, called retroreflectors, were left on the Moon and are still used today.

During several Apollo missions, astronauts placed special mirror-like devices on the Moon's surface. These aren't just regular mirrors; they're designed to bounce laser beams sent from Earth right back to where they came from. Scientists on Earth have been shooting lasers at these reflectors for over 50 years. By measuring the exact time it takes for the laser light to travel to the Moon and back, we can measure the distance to the Moon with extreme accuracy, down to just a few centimeters. This ongoing experiment proves that something was indeed placed on the Moon by humans, and it's still there. No one could have secretly placed these large, precise instruments there without anyone noticing.