Mischievous, capricious, boisterous Sun never took her cosmic duty seriously in her younger days.
Many cast light upon the mortal world, but only one, only Sun cast warmth upon the mortal world.
For Sun was always laughing. Always. And her great warmth came from her perpetual laughter.
Her elder sister, Moon, cast a light that was calming and dim enough to let other lights shine, like the stars and the planets.