Well, I don't know what to say. MLP doesn't belong to me... A little song dedicated to the other co-ruler of Equestria, guardia of the day and queen of the sun: Celestia. (I speak spanish, so go easy on me, please) I tried that this song has a similar story, in some parts, to "The Dark Side of the Moon".
The blind sun.
This is a history forgotten
a thousand years ago,
about two sisters
that ruled the world.
One was the princess of a gorgeous night
and a lovely moon.
The other one was the princess of a shining day
and a blind sun.
The big one, that can shine like the sun,
has the control of the day.
The little one, beautiful like the moon,
the night had on her hooves of clay.
As the days and nights passed,
Luna noticed something:
everypony played on her sister's day,
and sleep on her beautiful well-controlled thing.
A day she refused to lower the moon,
Astonishing her sister with blind eyes.
She couldn't notice what happened
before her pink eyes.
A eternal night she will bring
If Luna doesn't come back,
so she used the Elements of Harmony
without time of lack.
"Goodbye my sister,
I will see you soon,
when the time has come
to lower the moon."
Celestia's powers controlled the day and the night,
giving everyponi the glow of the moon and sun.
The sorrow hurting her heart,
'cause she was too blind…
The dawn, the night,
two times of day.
The light, the dark,
complement in one unique way.
Now separate of eachother,
the harmony is almost broken
and being guilty for all of her life
is the punishment of
the blind Sun.