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Mercury makes its rare move across the sun

The planet Mercury is passing across the sun Monday in a rare celestial event, but don’t expect to just look up and see it.

Mercury will appear as a small black dot that began crossing the sun at 7:12 a.m. and will continue until 2:42 p.m. Monday.

According to NASA, the phenomenon only happens about 13 times a century, when the orbits of Earth, Mercury, and the sun line up. The “Mercury transit” last occurred in 2006, and won’t happen again until 2019, said Kathy Reeves, a solar astrophysicist at the Harvard–Smithsonian Center for Astrophysics.

“It’s a relatively rare event,” Reeves said. “The orbits are actually a little bit tilted, so Mercury and Earth don’t always line up right so that we see Mercury and Earth pass in front of the sun.”

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The East Coast is the best place to view the transit in full, Reeves said, since the sun rose earlier.

To view the transit, one would need a telescope or high-powered binoculars with solar filters, since Mercury is so small and the sun is harmful to the naked eye, Reeves said.

An easier way to watch the event? An online live stream.

Since Mercury is far away from Earth and is so small in comparison with the sun, the transit will have no noticeable effect on the light emitted from the golden disk through Monday. A Mercury transit pales in comparison to a solar eclipse, during which the moon passes directly in front of the sun.

The top of the Stratosphere tower was silhouetted as the planet Mercury was seen, lower left quadrant, transiting across the face of the sun from Las Vegas.
The top of the Stratosphere tower was silhouetted as the planet Mercury was seen, lower left quadrant, transiting across the face of the sun from Las Vegas. David Becker/REUTERS

Live tweets from NASA