Mercury is in the middle of a rare trip across the sun, and almost everyone in the US should be able to catch at least a glimpse—with modest gear and safety protections. The official term is a "transit," and Mercury showed up as a small black dot about 7:35EST and will work its way across the sun for five and a half hours, per Sky and Telescope. The planet will be at the midway point at 10:30EST and slip away at 1:04EST. Those watching will want to pay particular attention to the final moments. "Mercury will temporarily look as though it's anchored to the edge of the sun, forming a teardrop shape," per Smithsonian.
Need an incentive to check it out? Mercury makes only 13 or so transits a century, and while the most recent was in 2016, the next won't be visible from Earth until 2032. However, the next one visible from the US won't take place until 2049. Sky watchers won't see anything with the naked eye—and don't try because it's dangerous—so binoculars or telescopes are necessary. Sky and Telescope and Space.com have details on specs, and both emphasize the need for solar filters for protection. Also of note: Don't use those special glasses for solar eclipses, because they might actually make the danger worse in this case. The spectacle also will be visible at various places online, including at NASA and Slooh. (Read more Mercury stories.)