Learn all about the Mercury Transit on November 11. Also this month, you can "observe the regular dimming and brightening of the 'Demon star,'" according to NASA's Jet Propulsion Laboratory. -- Mercury Transit 2019: Here's Why This Celestial Event Is So Rare: https://www.space.com/mercury-transit-2019-why-its-rare.html
Algol animation is licensed as CC-BY-SA 3.0. Video credit NASA-JPL/Caltech.