First and foremost, protect your eyes.

Tomorrow morning, Monday November 11th around 4:35 a.m. PST, sky watchers around the world will have the opportunity to witness a rare celestial treat.

Mercury is due to pass across the sun, an event known as a transit. The smallest planet’s next transit won’t be visible from Earth until 2032, and those who live in the United States won’t be able to see a transit until 2049. So provided that you have the proper equipment—or access to a good webcast—now is your chance to take a look.

Mercury will appear to be just one-194th the size of the sun—a small, dark speck moving across a huge, blazing surface. The planet is, in fact, small enough that you won’t be able to see it without a telescope or pair of binoculars—and you must make sure that your equipment is kitted out with a safe solar filter. Do not try staring directly into the sun; you won’t see anything, and it’s dangerous. And don’t use solar eclipse glasses to look through binoculars and telescopes. The lenses will amplify the sunlight hitting your eyes.

If you don’t have the proper viewing equipment, you can watch short movies of the transit on a NASA platform. The first three hours or so will not be visible on the west coast, the entire event lasts five hours and 28 minutes.

earthsky.org 2016 Mercury transit

Mercury’s and Earth's orbits intersect twice during each revolution around the sun, currently in early May and November. But we don’t see transits every year because planets take different amounts of time to make their way around the sun, and thus do not always meet at the two points of overlap. When they do, if Earth and Mercury arrive at these points, called nodes, at the same time, you have a transit.

On average, there are 13 transits of Mercury each century. Venus transits happen in pairs, with eight years separating the two events—and more than a century passes between each transit duo. We won’t be able to see Venus’ next sojourn across the sun until 2117.

One nifty phenomenon to watch out for is the "black-drop effect," which happens when the planet is about to enter or leave the solar disk. If you happen to see it—the effect is easier to spot with Venus—Mercury will temporarily look as though it anchored to the edge of the sun, forming a tear drop shape.