On November 11, 2019, NASA’s Solar Dynamics Observatory captured Mercury’s transit of the sun. It lasted from approximately 7:00 am to 1:38 pm ET (1200 to 1808 UTC). What exactly is a transit? Nicholas St. Fleur explains:
Cosmically speaking, a transit is when a celestial body — like a planet or moon — moves between a larger object and some observers, typically us on Earth.
The most famous transit is a solar eclipse, when the moon passes in front of the sun, like during the 2017 Great American Eclipse. There is also a lunar eclipse, where Earth passes directly between the sun and the moon, casting a reddish shadow on the lunar surface.
Because Earth is the third planet in our solar system, we can see the transits of Mercury and Venus.
From Bruce Betts at The Planetary Society:
Mercury transits occur about 13 to 14 times per century. The last one was in 2016, but the next isn’t until 2032. The timing is tied to not only the interplay of the orbital periods of the two planets, but also the relative tilt of the two orbits. Mercury’s orbital plane is tilted a few degrees relative to Earth’s orbital plane. The Sun-Mercury-Earth line-up can only occur when Mercury is passing through the plane of Earth’s orbit, and only if that occurs when Earth is in the right part of its orbit.
NASA’s Solar Dynamics Observatory (SDO): Year 5 and Venus crossing in front of the sun.