Once upon a time, when there were no people, Gaea (Earth) lived with her daughter. (Luna) They lived happily together and Luna always showed her face with a radiance parallels only by Sol, her father.
However, as Luna grew into a teenager, she grew more and more moody. Soon, she began to cover her eye with her night black hair. This continued for a while and Gaea though nothing of It, for it was merely a phase, in her opinion that is.
Luna would add a little more hair each night. Finally, after about half a month, her hair covered her whole face. Gaea realized this would not do as all the creatures who awoke on the night would have no light to see. So, she and Sol got together with Luna and persuaded her to pull her hair back.
Luna agreed to this and pulled back a littlest each night. When she once again shown with all her radiance at the end if the month, she got upset and moody again that her parents had made her in over her face, for she could do as she wished.
So, once again Luna began to cover her face and once again her parents made her pull it back again when her face s completely covered. This cycle has continued ever since and will continue ever more. That is why we have the phases of the moon.
