Mycroftxxx

The biggest clue as to what's happening in Equestria every morning is revealed in The Crystal Empire. Cadence is exhausting herself trying to keep control of the Empire, and as she's fading you can see the "skybox", for lack of a better term" switching over to the view Sombra prefers. Outside of the Empire, deep winter or arctic snow continues to rage, while the environment inside is preserved by magic. Celestia and Luna do the same thing. They aren't controlling the spin or orbit of the planet, or moving a tiny sun and moon. They're changing the skybox settings. This is why Celestia can be defeated in battle - she's not a star-breaking diety. This is why the ponies of Equestria handle local weather manually. Hell, this is why the sky showed both sun and moon in the sky when the Princesses were indisposed during the season 4 opener. Nearly everything points to Equestria being a synthetic environment controlled by magic. I generally view the kingdom as being like the giant set in The Truman Show. Amusingly enough, the immortality of the princesses is also questionable - Granny Smith pre-dates Ponyville, which Twilight Sparkle implies has been around for "hundreds" of years. If the total lifespan of a pony is in the range of multiple hundreds of years, Celestia may have only lived through three or four lifetimes.