The Eclipse Beam is a device from the 1985 animated series She-Ra: Princess of Power.
She-Ra: Princess of Power
The Eclipse Beam was strong enough to destroy Castle Bright Moon by using the power of an eclipse of the moon. The idea was to break through Queen Angella's defenses as her powers are provided by the Etherian moons. The Eclipse Beam was to fire a laser beam right at the castle and destroy it.
After their King and Queen were freed thanks to Bow and Spunky, the Twiggets teamed up with She-Ra to destroy the machine. But Catra appeared to have the last laugh when she revealed that the machine had been a decoy and that the real Eclipse Beam was still aimed at Bright Moon.
She-Ra and Swift Wind managed to buy some time holding back the eclipse by physically moving Etheria's moon, while Bow used his harp, broadcast through an amplifier, to destroy the real Eclipse Beam with the vibration of a well-tuned note.