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Q. Why was Johannes Kepler's work vital to astronomy? — Sara B.
A. Johannes Kepler was an astronomer born in Germany. He worked there in the 1500s.

At the end of that century, in 1594, he began work on physical laws about how planets move around our Solar System.

Observers had thought that the Universe was a perfect construction with planets traveling in perfect circles. Then Kepler took a look at previous work by astronomers such as Denmark's Tycho Brahe and was able to show how a planet like Mars, for example, did not have an orbit that was a perfect circle. In fact, its orbit formed an ellipse, as did the orbits of all the planets of the Solar System.

This changed everything that had been assumed all the way back to ancient Greece. Isaac Newton used Kepler's laws of planetary motion in his own formulations of the laws of gravity.

The Universe as we know it was less perfect and more realistic from then on.



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