On Monday, November 11, 2019, stargazers will be treated to an unusual sight: our solar system's smallest planet, Mercury, passing between the Earth and the Sun. The rare event, called a transit, will be the fourth of just 14 transits of Mercury that will occur during the 21st century. The last one took place on May 8, 2016, and the next will not occur until November 13, 2032. However, it will not be visible from North America, which means the continent's residents will have to wait until May 7, 2049, to observe the celestial delight again.