Luna nodded.  Seeing the look on Celestia’s face, she raised a hoof.  “Not about the eternal darkness, of course.  We know thy ponies need your sun for thy crops to grow.  We know that were we to prevent the sun from rising, starvation and eternal winter would destroy all Equestria.”  She paused, considering her next words carefully.  “But, so few of thy ponies enjoy our night, sister.  We toil so maintaining our beautiful tapestry overhead, and shifting the shape of our moon, while it seems that all you do is set the sun on the same track every morn.  The only variance is how many clouds the pegasi hath put in the sky.  Yet, everypony would rather be out in the day.”