Watch Mercury Make a Rare Transit Across the Sun on Monday

The planet won’t transit the Sun again until 2019.

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May 9 2016, 9:00am

Image: NASA

Skywatchers around the world are about to be treated to a rare celestial event—the transit of Mercury across the Sun. Starting at 7:12 AM EST on Monday, May 9, the solar system's innermost planet will pass in front of our star from our perspective, journeying west across its face until it completes the trip over seven hours later.

It's been nearly a decade since Mercury made its last transit, and it will be another three years before the next one occurs, so both professional and amateur astronomers are eager to break out their telescopes to watch the event unfold. The eastern chunk of North and South America will have the most optimal view of the planet's passage, while Australia, New Zealand, and eastern Eurasia will be jilted this time around.

Naturally, special solar filters are required to view the transit, both because Mercury is incredibly small and because staring directly at the Sun through a telescope is one of the most surefire ways to burn out your retinas. But if you don't have the right instruments or are not at the right location to watch the proceedings, no sweat, because there will be numerous livestreams covering the event, including ones hosted by Slooh, Sky & Telescope, NASA, and the European Space Agency.

Planetary transits make for a great excuse to observe celestial dynamics in action, but they also provide a unique opportunity for scientists to extract more precise details about distant worlds. When Mercury is intensely backlit by the fury of our main-sequence star, for instance, it's a lot easier to pick out features about its surroundings.

"When Mercury is in front of the Sun, we can study the exosphere close to the planet," said NASA planetary scientist Rosemary Killen in a statement. "Sodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption, we can learn about the density of gas there."

What's more, past observation of transiting planets like Venus and Mercury has dramatically shaped our modern search for exoplanets, most of which are discovered when they transit their own stars. It goes to show that even a tiny planet like Mercury can usher in huge discoveries when it has its moment in the spotlight.