Rambam, Hilchos Yesodei Hatorah Chapter 3. From Chabad.org
The spheres are called the heavens, the firmament, the habitation, the skies.
There are nine spheres. The closest sphere is the sphere of the moon. The second sphere, which is above it, is the sphere which contains the planet Kochav (Mercury). The third sphere, which is above it, contains [the planet] Noga, (Venus). The fourth sphere contains the sun. The fifth sphere contains [the planet] Ma'dim (Mars). The sixth sphere contains the planet Tzedek. (Jupiter). The seventh sphere contains [the planet] Shabbtai (Saturn). The eighth sphere contains all the stars which are seen in the sky. The ninth sphere is the sphere which revolves each day from the east to the west. It surrounds and encompasses everything.
All these [nine] spheres which surround the world are spherical like a ball, and the Earth is suspended in their midst.