28 000 B.C - Cro-Magnon people sketch moon phases on tools made out of bones, 4236 B.C - Egyptiens adopt a 365-day calendar based on the movement of the star Sirius, A.D 900s - Arab astronomers improve the accuracy of the Greek astrolabe, a tool for celestial navigation. , 1054 - Chinese astronomers document the explosion of the supernova that creates the Crab Nebula, 1608 - The telescope is invented, allowing astronomers to discover planets such as Uranus and Neptune, moons, and stars that are invisible to the naked eye. , 1860 - The invention of spectroscopy suggests that the celestial bodies are composed of some of the same elements that make up Earth's atmosphere, 1957 - Russia launches the first two satellites into orbit around Earth, marking it the beginning of space exploration. , 1990 - The United States astronauts become the first humans to walk on the moon. , 2004 - A Mars rover discovers rock formations and sulfate salts indicating the planet once had flowing water. ,

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