Mercury is passing 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 began shortly after 7 a.m. ET on Monday and will continue for more than seven hours.
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. NASA stresses 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, NASA says.
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 1631, the transits were later used to “measure the distance between the Earth and the Sun,”NASA said.
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.
This phenomenon is “the main way we find planets outside the solar system,” NASA says.
The Kepler mission, which is searching for habitable planets, has found 1,041 planets to date using the transit method. The mission says it is able to determine the size of a planet by observing its transit.
Image Credit: NASA
Mercury is on the move! -Emily