Robert Fludd (1574-1637) was one of the most significant writers on hermetic philosophy. His major work was his remarkable thousand page 'History of both worlds' which is a survey of the knowlege in his time about the Macrocosm, the external cosmos, and the Microcosm or the world of Man.
In the opening section of his work he discusses the nature of the various heavens, the Empyrean, the Aethereal and the Elemental Heavens.
Here Fludd discusses the nature of light, the formation of the fixed stars, the Sun and the planets.