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Rare Mercury Transit, the Last Until 2032, Thrills Skywatchers Around the World

The tiny planet Mercury scooted across the sun's face today (Nov. 11) for the last time until 2032, and skywatchers around the world had the chance to witness the rare celestial event. 

During this 2019 transit of Mercury, the innermost planet spent about 5.5 hours crossing in front of the sun from our perspective on Earth. Skywatchers across the Americas, Africa and Europe could see at least part of Mercury's journey across the sun, but only with telescopes or high-power binoculars equipped with protective solar filters. Meanwhile, several spacecraft, including NASA's Solar Dynamics Observatory, provided views of the event from space. 

Mercury's silhouette began to encroach on the sun's disk at 7:35 a.m. EST (1235 GMT), when the sun was above the horizon for viewers in South America, eastern Central America and the U.S. East Coast. In the rest of the U.S., Mercury was already making its way across the sun by sunrise. In most of Africa and Europe, Mercury was still crossing the sun as the sun dipped below the western horizon. 

Related: The Mercury Transit of 2019 in Photos! The Best Views Until 2032
More: Here's Why Mercury Transits Are So Rare

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The beginning of the Nov. 11, 2019, transit of Mercury was studied by the Helioseismic and Magnetic Imager instrument on NASA's Solar Dynamics Observatory satellite.

The beginning of the Nov. 11, 2019, transit of Mercury was studied by the Helioseismic and Magnetic Imager instrument on NASA's Solar Dynamics Observatory satellite. (Image credit: NASA/SDO/HMI/AIA)
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Instruments onboard NASA's Solar Dynamics Observatory study the sun in a range of different wavelengths to learn more about the star. This image of the transit of Mercury was captured by the satellite's Atmospheric Imaging Assembly instrument.

Instruments onboard NASA's Solar Dynamics Observatory study the sun in a range of different wavelengths to learn more about the star. This image of the transit of Mercury was captured by the satellite's Atmospheric Imaging Assembly instrument. (Image credit: NASA/SDO/HMI/AIA)
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Another view from the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory shows Mercury approaching the sun's disk on Nov. 11, 2019.

Another view from the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory shows Mercury approaching the sun's disk on Nov. 11, 2019. (Image credit: NASA/SDO/HMI/AIA)
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Mercury transited the sun on Nov. 11, 2019, as seen from Washington, D.C.

Mercury transited the sun on Nov. 11, 2019, as seen from Washington, D.C. (Image credit: NASA/Bill Ingalls)
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Another view from the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory shows Mercury approaching the sun's disk on Nov. 11, 2019.

Another view from the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory shows Mercury approaching the sun's disk on Nov. 11, 2019. (Image credit: NASA/SDO/HMI/AIA)

Mercury transit from Earth and space

While people on the ground carefully examined the sun and shared videos and photos on Twitter, astronomers shared their view of the action through sun-gazing telescopes. Technicians with NASA’s Solar Dynamics Observatory posted near real-time imagery and video of the Mercury transit in ultraviolet and visible wavelengths. Meanwhile, the European Space Agency’s Proba-2 mission was snapping images as well, according to an ESA tweet, although those photos haven't been released yet.

As of the final minutes of the transit, there was no word on whether the six astronauts on board the International Space Station would try to catch a glimpse of the transit. The Expedition 61 crew is equipped with astronomical observing equipment as well as cameras to catch celestial events, and they did gather footage during the 2017 solar eclipse.

On Twitter and in interviews, NASA and ESA used the opportunity to highlight current and upcoming missions to examine exoplanets and Mercury itself. NASA heliophysicist Alex Young told Space.com that the Mercury transit is similar to how the Transiting Exoplanet Survey Satellite (TESS) searches for exoplanets, as they travel across their parent stars.

ESA highlighted three of its missions on Twitter: BepiColombo en route to Mercury, the ESA Solar Orbiter that is getting ready for launch in 2020 to study the sun, and the Characterising Exoplanet Satellite (CHEOPS) that will also search for exoplanets using the transit method after its launch in December.

Transits of Mercury are relatively rare events, with about 13 happening every century, on average. The last Mercury transit was on May 9, 2016, and the next one will be on Nov. 13, 2032. Skywatchers in the U.S. won't get another Mercury transit until May 7, 2049. 

How Mercury transits occur

Mercury and Venus are the only two planets that can transit the sun from Earth's perspective, because they are the only planets whose orbits are closer to the sun than Earth's. Venus last passed before the sun on June 6, 2012, and the next Venus transit isn't until Dec. 11, 2117. These transits happen because the planets' orbits are slightly tilted to the ecliptic, or the plane of Earth's orbit, and those orbits intersect at two places called "nodes." Transits occur when Earth crosses a node at the same time as the other planet. In Mercury's case, this always happens in May or November. For Venus, transits occur in June and December. 

Amateur astronomers and astrophotographers around the world took heed of today's rare celestial treat and (weather permitting) captured some incredible images of Mercury as it inched across the sun like a tiny, traveling ink blot. With an apparent diameter of 10 arc seconds, Mercury's width was about 0.5% that of the sun. In terms of area, the tiny planet covered only 0.003% of the sun's disk. To see the little fleck on the sun, observers had to use magnifying equipment with special solar filters; it was too small to see with solar eclipse glasses. 

A view from the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory shows Mercury approaching the sun's disk on Nov. 11, 2019. (Image credit: NASA/SDO/HMI/AIA)

Though the Mercury transit was not visible everywhere in the world — like Asia, Australia and Alaska, where it happened at night — anyone with an internet connection could still follow the event live online, thanks to astronomy webcast services like Slooh and the Virtual Telescope Project. NASA's Solar Dynamics Observatory also provided near-real-time views of the sun from space. These telescopes offered some solace to viewers across the midwestern and northeastern U.S., where overcast skies made it difficult for many eager transit-watchers to get a good view of the sun. 

While skywatchers across the globe celebrated the rare chance to see a Mercury transit today, scientists also took the opportunity to learn more about the innermost planet — particularly its thin atmosphere. When Mercury passes in front of the sun, scientists can observe changes in sunlight that passes through its tenuous atmosphere, allowing them to study its elemental composition. 

Waiting for 2032

Mercury transits are rare celestial events. Here's a look at how they happen and why from our print sister publication All About Space magazine. (Image credit: Future Plc/All About Space Magazine)

It will be 13 years before Mercury transits the sun again and 30 years until it happens again in the U.S. — but if you got special gear to watch this transit safely, don't ditch those solar filters just yet! You can use the same solar filtered-telescopes and binoculars to watch some solar eclipses before the next transit, so long as the filters are not damaged.

Solar eclipses, when the moon blocks at least a portion of the sun's disk, occur about two to five times per year, with total solar eclipses — when the moon completely blocks the sun from view — occurring about once every 18 months, on average. To find out when the next solar eclipse will be visible near you, check out this handy list of eclipses with interactive maps from timeanddate.com. 

Editor's note: If you captured an amazing photo of the Mercury transit, or any other celestial sight, and you'd like to share it with us and our partners for a story or image gallery, send images and comments in to Editor-in-Chief Tariq Malik at spacephotos@space.com.

Email Hanneke Weitering at hweitering@space.com or follow her @hannekescience. Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook.

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  • rod
    FYI, this was a thrill, a great event to observe! My first Mercury transit. I was out early and at 0713 EST, the Sun rose above a tree line on the horse farm I viewed from. At 40x, I could see Mercury black disk shape on the solar limb near 0737 EST, that was 2nd contact of ingress. Temps were near 5C with dew and light fog around, cirrus clouds too. I observed through out the day and viewed Mercury from 40x to 71x. Near 1200 EST, the cirrus clouds started moving away with plenty of blue sky. The last 60 minutes of the Mercury transit, skies provided great views at my location. Near 1302 EST at 71x, I could see Mercury next to the solar limb, soon to depart. By 1304 EST, Mercury no longer visible. I used my flip, cell phone for time checks 😊 Outdoors today, some deer hunters were using their muzzle loaders. I was out in the fields with my hunter's orange on. Two immature eagles were flying around me and my pasture areas, distinct calls and sight. Likely young eagles that have not departed the nesting areas for winter. Various flocks of birds flew across my telescope view too, especially early shortly after Mercury ingress near 0735 EST. I used my 90-mm refractor with white light solar filter, 25-mm plossl and 14-mm eyepieces. The tripod is alt-azimuth with cable, slow motion controls. The Sun is a bit more than 0.5-degree diameter in the field of view and Mercury near 10" angular size. Quite a sight in the telescope view! My eyepieces provided 1.3 and 1.0 degree, true field of views. Even though at times cirrus clouds moved by, the cirrus did not block out my views of the Sun and Mercury. The next Mercury transit viewable in my location will be 07-May, 2049 or nearly 30 years. My stargazing log is all updated.
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  • Michael Amato
    My brother & I also went to the Southern Connecticut beach early in the morning. We viewed the transit with my Sunspotter Solar Telescope. We were able to watch Mercury cross half the sun's face before clouds moved in. We have now seen two Venus & two Mercury transits. It was great.
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