Luminous objects emit their light, while non-luminous objects do not. The sun, for example, is a luminous object because it emits its own light. The moon, on the other hand, is a non-luminous object because it does not emit its own light. Instead, the moon reflects light from the sun.

The earth is a non-luminous object because it does not emit its own light. Instead, the earth reflects light from the sun. This is why we can see the earth from space.