The Science of the 2019 Mercury Transit: How Astronomers Will Study the Rare Celestial Event

Mercury as seen passing between Earth and the sun during a transit. (Image: © NASA's Goddard Space Flight Center)

Monday’s transit of Mercury will provide an opportunity for students to re-create history.

Nola Taylor Redd |

On Monday (Nov.11), observers and scientists in North America will have their last opportunity to view a rare celestial event for three decades.

Mercury will cross in front of the sun, as seen from Earth, a process known as a transit. Although the last transit of Mercury occurred only three years ago, the next won’t happen until 2032 and won’t be visible from North America. These rare events provide the opportunity for scientists to gather both new scientific observations and re-creations of historical ones. 

Because it is closer to the sun than Earth, Mercury constantly passes between our planet and our star. But its orbital plane doesn’t quite line up with Earth’s, so most of the time it appears to dip either above or below the sun when seen from our planet. Only when Mercury’s orbit crosses the plane of the Earth as it appears in line with the sun is a transit visible. Such transits are rare; this will be the fourth of 14 to happen this century. (Venus also transits the sun, but even more rarely, occurring in pairs separated by a century from the last set.)

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