- 2 September 1988 – Australia Telescope Compact Array (ATCA), which first imaged a radio supernova remnant as it formed, has its first light.
- 5 September 1977 – Space probe Voyager 1 is launched on a mission to study Jupiter and Saturn
- 8 September 1966 – The first episode of a new television science fiction series "Star Trek" is shown on NBC-TV
- 12 September 2013 – NASA announces that 19 days earlier, Voyager 1 had become the first man-made object to cross the heliopause and enter interstellar space
- 15 September 2017 – The Cassini spacecraft plunges into the atmosphere of Saturn, ending its 13-year tour of the ringed planet
- 21 September 1866 – Science fiction writer, H. G. (Herbert George) Wells is born, in England
- 23 September 1846 – The planet Neptune is discovered by Johann Gottfried Galle using mathematical equations from John Couch Adams and Urbain Le Verrier
- 29 September 1971 – The Orbiting Solar Observatory 7 satellite launches with the first x-ray observations of a beginning solar flare and of solar streamers
