Portal:History of science/Selected anniversaries/May 15

1618 - Johannes Kepler accepts that "the ratio which exists between the periodic times of any two planets is precisely the ratio of the 3/2th power of the mean distances"—the third law of planetary motion. According to his account in the eighth section of the third chapter of the fifth book of Harmonice Mundi, it was "conceived mentally" on March 8, 1618, but initially rejected based on a preliminary calculation.
1720 - Birth of Maximilian Hell, Slovakian astronomer (d. 1792)
1836 - Francis Baily observes "Baily's beads" during an annular eclipse.
1857 - Birth of Williamina Fleming, Scottish-American astronomer (d. 1911)
1859 - Birth of Pierre Curie, French physicist and Nobel Prize laureate (d. 1906)
1951 - Birth of Frank Wilczek, American physicist, Nobel Prize laureate
1957 - Britain tests its first hydrogen bomb in Operation Grapple.
1958 - The Soviet Union launches Sputnik 3.
1960 - The Soviet Union launches Sputnik 4.
1963 - NASA launches the last mission of the Mercury program, Mercury 9
1991 - Death of Andreas Floer, German mathematician (b. 1956)
2004 - The largest known prime number at the time of its discovery, 2^24036583 − 1, is found by Josh Findley and the GIMPS collaborative effort.