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Galaxies Exist
Edwin Hubble shows that galaxies exist outside the Milky Way galaxy. exact date is unknown. -
Liquid Rocket Fuel
Robert Goddard uses the first liquid rocket fuel. -
Center of the Milky Way
The oort cloud shows that the center of the Milky Way galaxy is in Sagittarius. -
Pluto
Clyde Tornbaugh discovers Pluto. -
Cosmic Radio Waves
Karl Jansky discovers cosmic radio waves. -
Radio Telescope
First radio telescope built by Grote Reber. exact date is not known.