Question #52 – The planet Mercury will transit the Sun today. What does this mean?
A transit occurs in space when a small object passes in front of a larger object. Today, the planet Mercury will travel across the face of the Sun between 7:30 a.m. and 1:00 p.m. Transits of the Sun by Mercury are relatively rare, with around a dozen occurring every century. Mercury will not transit the Sun again until November 13, 2032.
See this Wikipedia page for more information about transits of Mercury. Also, be sure to watch NASA's A Mercury Transit Music Video from SDO, and watch the transit live at NASA's 2019 Mercury Transit page.