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Stargazers, ready your (solar-filtered) telescopes: Mercury is about to pass directly across the sun for the first time in nearly a decade.

The innermost planet of our solar system will look like a small, dark circle cutting across the sun's disc. In the U.S., the transit will begin shortly after 7:00 a.m. ET on Monday and continue for more than seven hours.

In this animation, NASA shows Mercury's expected path across the sun Monday, hour by hour:

At least part of the transit, which only happens about 13 times every century, will be visible across the Americas, Europe, Africa and large portions of Asia.

If you're hoping to watch it, eye protection is key. 

 that "viewing this event safely requires a telescope or high-powered binoculars fitted with solar filters made of specially-coated glass or Mylar."

You won't be able to see the tiny dot of Mercury on its celestial crawl without magnification, 

Another option: Check out one of the multiple live-streaming events going on Monday. NASA says it will stream the transit 

NASA's main stream will start at 7 a.m. The Europeans have already started talking about the upcoming event:


It's not all about the show — transits like this one have historically been, and continue to be, important research opportunities for scientists. First observed in the 1631, the transits were later used to "measure the distance between the Earth and the Sun," 


Now, they provide scientists an opportunity to study the planets' exospheres — the thin layer of gases that make up their atmosphere.


"When Mercury is in front of the sun, we can study the exosphere close to the planet," NASA scientist Rosemary Killen said in a release from the Jet Propulsion Laboratory. "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."


Additionally, scientists have found that a transiting planet causes a drop in the sun's brightness. The subtle change on the light curve can be seen in this example animation from 

 (Scroll down to "The Science ... Why are Planetary Transits Important")


This phenomenon is "the main way we find planets outside the solar system," 


The Kepler mission, which is searching for habitable planets, has found 

 it is able to determine the size of a planet by observing its transit.


Wondering what that black dot looks like up close? NASA recently released 

 taken from the MESSENGER spacecraft, the first to orbit Mercury.

Science

Stargazers, ready your (solar-filtered) telescopes: Mercury will pass directly across the sun on Monday for more than seven hours. And you can watch when it does -- if you do it just right.

Mercury to cross in front of sun in rare event. Here's how to watch

Go Deeper.

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