The solar system鈥檚 smallest planet will appear as a tiny black speck slinking across the sun Monday morning, in a rare celestial event.

The transit of Mercury, the innermost planet, began Monday morning around 7:35 a.m. EST. Weather permitting, the planet鈥檚 trip across the sun will be visible to most of the world for more than five hours.

鈥淭hough it takes Mercury only about 88 days to zip around the Sun, its orbit is tilted, so it鈥檚 relatively rare for the Sun, Mercury and Earth to line up perfectly,鈥� writes .

The phenomenon only happens 13 or 14 times a century and it will be 30 years before North Americans see another one. While the next Mercury transit between Earth and the sun will happen 13 years from Wednesday (in 2032), it won鈥檛 be visible from North America until the next occurrence in 2049.

As always, it鈥檚 not safe to stare at the sun with the naked eye, though it won鈥檛 be visible anyway, without a telescope or binoculars fit with solar filters. NASA solar astrophysicist Alex Young told The Associated Press that it would take 鈥�exceptional vision鈥� to spot Mercury鈥檚 transit. It鈥檚 the smallest planet at about one-third the size of Earth (a ). Young could barely see Venus, which is a larger, closer planet, in 2012 with solar-filter glasses when it made a trip across the sun.

鈥淭hat鈥檚 really close to the limit of what you can see," he told AP. "So Mercury鈥檚 going to probably be too small.鈥�

Earthlings can safely watch Mercury transit from the comfort of their own homes via various live-streams online, including a in Los Angeles, which begins at 9:15 a.m. EST.

It will take more than five hours for the planet to finish the trip, but Mercury will actually be moving at about 241,000 km/h.