Celestia pondered her answer.  There was no point in lying to Luna, for she would know the lie and brood on it.  Instead, she said simply, “The sun is more important to their survival, Luna.  You know that.  There is little I can do with it without causing crops to wither or freeze.  Imagine the panic in the streets if I were to raise the sun closer than usual one day, or send it on a different course across the sky.  Perhaps if I had introduced some variation in the early years, ponies might have grown to expect it, but now it is too late.”