The moon and Earth are examples of non-luminous objects. Non-luminous objects become visible only when they reflect light produced by a luminous object. A luminous object, such as the sun, emits its own light, because it has its own source of energy.
According to Penn State University's Astrology Department, the Moon has a very dark surface that only reflects about 3 percent of the sun's light. The moon's cycle is determined by the amount of light that reflects from the moon's surface in relation to its position in orbit around Earth. When only half of its surface is lit, this is called the first or third moon quarter. As Earth and the moon orbit the sun, Earth regularly blocks the moon from the sun completely; this is called a new moon. A full moon is entirely illuminated by the sun's light.
Earthshine occurs when the Earth reflects sunlight onto the moon's surface when the moon is in its crescent phase. The crescent portion is brightly lit by reflected sunlight, while the rest of the moon dimly reflects light from the Earth. As this double-reflected light travels through space, it becomes even dimmer as some of it is absorbed into Earth’s atmosphere.