On May 9, if you happen to be staring at the sun, you could catch a glimpse of Mercury passing in front of it. You’ll also damage your eyes.
Visible only as a tiny speck, the planet will take about seven and a half hours to cross the diameter of the sun. It will take so long that nearly every country (sorry, Australia) will get a chance to see it.
This rare event, called a solar transit, happens only about once a decade-- the last one for Mercury was in 2006. Understandly, some of the nerdiest parties in the world are being planned for the viewing.
To join the festivities, you'll need a telescope or a solar filter to witness the transit—or you can just watch it on NASA TV, where it will be streamed live.