Mercury passed in front of the sun today. It was the first time that Mercury had passed between Earth and the Sun since 2006, and it was something amazing to see.
Images of the event put into perspective just how tiny Mercury is (radius: 1,516 miles) compared to the Sun (radius: 432,288 mi).
But even a small planet like Mercury can block the light of the Sun, even if it’s just a small part of the Sun for a small amount of time. Transits like this one happen when exoplanets pass between their star and our telescopes.
As NASA took the opportunity to point out today in an Instagram post, the long-delayed James Webb Space Telescope will one day be able to determine the details of exoplanet atmospheres by watching the distant planets transit in front of their stars, just like we watched Mercury pass in front of the Sun today.