Ambar is the term for the Earth itself, excluding the celestial bodies, was Ambar or Imbar. It is the raw, solid, and pure earth that was the base and core of Arda before the change (during the First Age). Because the Sun, Moon, Stars, and other objects orbited the planet in the cosmology of Middle-earth, they were considered part of Arda, leading to Arda sometimes being called the 'Solar System' of Middle-earth.