When they say Princesses Celestia and Luna raise the sun and moon, respectively, what they really mean is that the royal sisters use their Alicorn magic to rotate the ponies' home planet (called Pony World) on it's axis.

Pony World's moon is called Pony Moon, of course.

Pony World's sun is classified as any other star, officially called the Pony Sun or simply the Sun unofficially. Pony Moon orbits Pony World. Pony World orbits the Pony Sun.

Pony World must be located in a solar system with other planets, which likely have their own moons, as well as asteroids, possibly an asteroid belt or two, and comets which have frozen asteroids as a nucleus.

When you view Canterlot from the outside on the show, you can see at least two observatories with their telescopes. They must study astronomy in Canterlot.