It was Johannes Kepler (of “Kepler’s Laws of Planetary Motion” fame) that first predicted transits of Mercury over the face of the Sun. He predicted the May 1607 event and November 1631 event. However, nobody knew how big (or small) Mercury would appear against the Sun, leading Kepler to misidentify a sunspot as the planet when he observed the the first prediction. Kepler was deceased by the time of the second event, but a French astronomer confirmed the transit took place.
The next Mercury Transit is set for 4-days from now: November 11, 2019. This blog will tell you all you need to know to view and image this rare sight!