Johannes Kepler

Halley´s approach. April 10, 1910.

Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime. Halley last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061 to 2062. Halley’s returns to the inner Solar System have been observed and recorded by astronomers since at least 240 BC. Clear records of the comet’s appearances were made by Chinese, Babylonian, and medieval European chroniclers, but, at those times, were not recognized as reappearances of the same object. The comet’s periodicity was first determined in 1705 by English astronomer Edmond Halley,...

The Galilean Moons. January 7, 1610.

As a result of the improvements Galileo Galilei had made to his telescope, now with a magnifying capability of 20x, he was able to observe celestial bodies more distinctly than it had been ever possible. On January 7, 1610, Galileo wrote a letter in which he mentioned Jupiter´s moons (actually known as the Galilean Moons) for the first time. At the time, he saw only three of the four and believed them to be fixed stars near Jupiter. In later observations he discovered the fourth moon and observed that they were not fixed stars, but rather bodies orbiting Jupiter. In 1605, Galileo had been employed as a mathematics tutor for Cosimo de’ Medici, and seeking patronage from his now-wealthy former student and his powerful family, used the discovery of Jupiter’s moons to gain it. On F...

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