...for a long time they thought the stars were gods or the fireplaces of the Dead. The real "Space Age" conceptually was when the first philosopher said they were "fiery stones" or something physical. They were fiery due to the intense friction of their daily motion around the Earth. Of course the Greeks couldn't understand a real 'Void' so they filled it with aether or crystalline clock-work, so it wasn't really "space". "Zeus" was imagined as the hard sphere of the 'sky' that everything was embedded in. Space didn't get conceived until the Middle Ages when the Scholastics broke with Aristotle and imagined real 'vacuum'. Thus eventually Kepler was one of the first to realise that Earth's atmosphere didn't reach to the Moon. And he proposed travelling somehow through space in that letter to Galileo.