Template:On This Day (nonfiction)/May 15
From Gnomon Chronicles
1618: Johannes Kepler confirms his previously rejected discovery of the third law of planetary motion (he first discovered it on March 8 but soon rejected the idea after some initial calculations were made).
1801: Mathematician Joseph Ludwig Raabe born. He will discover Raabe's ratio test, which determines the convergence or divergence of an infinite series, in some cases.
1836: Astronomer Francis Baily observes "Baily's beads" during an annular eclipse.
