Day and Night

Here' an interesting thought that passed my mind while I was reading stories here, and has refused to leave my head sense then...
Celestia and Luna control both the sun and the moon, respectively. How ever, they talk about their jobs as if they sleep when the other is taking charge. Now, in my logical mind, this does not make sense. Only because in order to have a sun or a moon, they would have to reside upon a celestial body. As logic/science dictates, the celestial bodies, called planets, that they live on are not flat, but spherical.
Now I can agree with them being able to control the sun and the moon, as this has been explained as Alicorns being utterly powerful in magic. How ever, that still raises questions. What about the other half of the world? Do they in fact, as immortal beings, not need sleep and take charge of the other side of the world as time passes? If so, then why have we not heard anything of the rest of said world beyond Equestria and the Crystal Empire? Even small remarks about intercontinental matters would be good.
I'm sure many fan fictions out there play on this fact, each with different views on the subject, however it doesn't change that there is nothing within the show on this matter. They did provide us a map of Equestria, however if Equestria makes up the entirety of the world, then even still half the world would be night, with half the world day. As this is proven as false with in the show, by the story of Applejack getting her cutiemark.
If we remember back to that episode, Applejack said her story. And if we are to assume the background is accurate, as well as the time perception with in her story, then her story took place all with in 3 - 4 days. If Equestria in deed was the whole world, then that would place it size relative to a large city here on earth. As such, the days would be incredibly shorter. Ergo, Applejacks story would have taken place through several 'earth' weeks. And may have been perceived as such, unless their perception of time is much slower then ours.
However, this does not make sense in the continuity of the show, as one episode they are in fall, the next winter is ending. This fact, implies that their perception of time is much faster then ours. I have indeed taken to account that the episodes may not be as closely placed in time as this implies. How ever had this be true, we'd have had Lesson Zero much sooner then it was. (Episode wise) Mainly because writing letters about what you learned about friendship each and every week, you'd run out after 2 or 3 months. Therefore, I conclude that under this premiss Their perception of time is faster then ours.
But, what if it's the same, and Equestria is all of the world? Well, then either the sisters have been lying to the ponies this entire time about controlling the sun and the moon, which would be very controversial. But this still raises a single point, where does the sun/moon go? One logical conclusion, albeit odd, would be they are in fact underground. But if this were so, then why hadn't anypony discovered the farce? Celestia herself gives us the answer in the map. To the north, we have the Crystal Empire. And if their reactions to the cold there are any sign, I don't see anypony going further north. To the south, and this is going by the map given by The Hub, we have a desert that hosts the Changlings. Nopony wants to pass them do they? To the west we have water, and I haven't seen word nor voice of any boats going off into that water. Once again, to the east we have, water. Thus each direction is covered by something the ponies don't want to cross, or can't. Them living underground, and not knowing, would be easily kept by these premises.
Yet, this rises even more questions. Why are they underground? Had something happened to the world above to cause them to shelter underground? If so, why do nopony remember? Had their memories been erased?
I could ramble on, taking anyones time who decides to read this, but I don't feel like being that rude. As you probably have gotten bored by now, and want to read something else, like a Nyx story, or other story. Now, I turn and ask you one thing. I plan on having the mane6 within my story, Chaos Controlled, leave Equestria along with Makavar, one of my OC that appear with in the story. Now, how should I play this? Do they discover they are underground, and decide to explore the world above? Or does a dignitary from a previously unknown country arrive, seeking help? Being sent to alternate reality, by a spell gone wrong?
That's for you to decide...