On Saturday April 17, the 1000-foot dish at Arecibo will be activated for amateur-radio Earth-moon-Earth (EME) contacts on the 432 MHz amateur band.

Many of the world’s large parabolic antennas (dishes) along with hundreds of amateur radio operators and their gear will swing around to track the moon when it rises. Volunteers will then use the EME transmissions to link up with other dishes and antennas worldwide via the moon. Signals are literally being bounced off the moon’s surface and back to other stations on Earth, where they are received some 2.5 seconds later.

More info: Echoes of Apollo