The Egg Moon is an object that appears in the anime series Sonic X. It is a semi-artificial moon created by Dr. Eggman when Eggman offered to "repair" the damage done to the Earth's moon by the Space Colony ARK.
Egg Moon Saga
After half of the Moon was destroyed by the Space Colony ARK's Chaos Emerald-powered Eclipse Cannon, Dr. Eggman, while trying to convince everyone that he had changed his evil ways, offered to repair the damage done by launching a mini-missile which replaced the missing half of the moon with a self-replicating metallic half in order to return the moon to its original shape, creating the Egg Moon. This, however, caused the moon to be placed in a solar eclipse on New Year's Day at sunrise.
In order to solve the problem of a world bathed in darkness, Eggman invented the Sunshine Ball to provide the world with light for the next few months it would take to repair the Egg Moon's software and pull it out of the eclipse. A few weeks into this however, Sonic the Hedgehog began to smash the energy towers that the reflected sunlight was being channeled into, turning him into a public enemy as a result of his actions. Sonic stated that the Egg Moon was deliberately controlled to continue orbiting with the Earth to maintain the solar eclipse, explaining that if the Egg Moon's ability to orbit the Earth was stopped, it would just stay in the same place in its orbit while the Earth traveled in its own rotating orbital pattern around the Sun. Sonic then unveiled that the Egg Moon, along with his Sunshine Ball business, were all part of a scam to easily get rich off from the citizens of Station Square.
At the same time, Rouge and Topaz both discovered a hidden facility that was transmitting a control signal to the Egg Moon, prompting an explanation from Eggman. Eggman planned on converting humanity to his side so there would be minimal resistance when he kidnapped the president in order to create his Eggman Empire. However, his plans were foiled by the combined efforts of Sonic's friends and Stuart, who managed to free the president and send Eggman and his minions on the run. While up in space, Knuckles destroyed the receiver on the Egg Moon, allowing it to continue in its natural orbit and go out of the eclipse, bringing sunlight to Earth once again while Eggman, Decoe and Bocoe were arrested.