Thousands of years ago, long before Equestria was founded, the day and night cycles were controlled by a group of unicorns who raised the sun and moon using their combined magic powers each day

However, this routine grew tiring, as the mortal unicorns died out, and not all of them were capable of learning the spell

Until one day, two orphans were discovered to have the power to raise the sun and moon on their own. A unicorn who could use her magic to control the sun, and a bat pony with the unique power to control the moon and see into ponies dreams

Noticing the two's unique powers, the great unicorn wizard, Starswirl adopted the two and turned them into alicorns, dubbing them Princesses Celestia and Luna, rulers of the newly founded land Equestria