Teachable Moments | November 7, 2019
A Teachable Moment in the Sky: The Transit of Mercury
In the News
It only happens about 13 times a century and won’t happen again until 2032, so don’t miss the transit of Mercury on Monday, Nov. 11! A transit happens when a planet crosses in front of a star. From our perspective on Earth, we only ever see two planets transit the Sun: Mercury and Venus. This is because these are the only planets between us and the Sun. (Transits of Venus are especially rare. The next one won’t happen until 2117.) During the upcoming transit of Mercury, viewers around Earth (using the proper safety equipment) will be able to see a tiny dark spot moving slowly across the disk of the Sun.
Read on to learn how transits contributed to past scientific discoveries and for a look at how scientists use them today. Plus, find resources for engaging students in this rare celestial event!
Why It's Important
Then and Now
In the early 1600s, Johannes Kepler discovered that both Mercury and Venus would transit the Sun in 1631. It was fortunate timing: The telescope had been invented just 23 years earlier, and the transits of both planets wouldn’t happen in the same year again until 13425. Kepler didn’t survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury. Poor weather kept other astronomers in Europe from seeing it. (Gassendi attempted to view the transit of Venus the following month, but inaccurate astronomical data led him to mistakenly believe it would be visible from his location.) It was soon understood that transits could be used as an opportunity to measure apparent diameter – how large a planet appears from Earth – with great accuracy.
After observing the transit of Mercury in 1677, Edmond Halley predicted that transits could be used to accurately measure the distance between the Sun and Earth, which wasn’t known at the time. This could be done by having observers at distant points on Earth look at the variation in a planet’s apparent position against the disk of the Sun – a phenomenon known as parallax shift. This phenomenon is what makes nearby objects appear to shift more than distant objects when you look out the window of a car, for example.
Today, radar is used to measure the distance between Earth and the Sun with greater precision than transit observations. But the transits of Mercury and Venus still provide scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.
Exosphere Science
Some objects, like the Moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded by an ultrathin atmosphere of gases called an exosphere. Scientists want to better understand the composition and density of the gases in Mercury’s exosphere, and transits make that possible.
“When Mercury is in front of the Sun, we can study the exosphere close to the planet,” said NASA scientist Rosemary Killen. “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.”
Exoplanet Discoveries
When Mercury transits the Sun, it causes a slight dip in the Sun’s brightness as it blocks a tiny portion of the Sun’s light. Scientists discovered they could use that phenomenon to search for planets orbiting distant stars. These planets, called exoplanets, are otherwise obscured from view by the light of their star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve (a graph of light intensity) could indicate an exoplanet orbiting and transiting its star. NASA’s Kepler space telescope found more than 2,700 exoplanets by looking for this telltale drop in brightness. NASA’s TESS mission is surveying 200,000 of the brightest stars near our solar system and is expected to potentially discover more than 10,000 transiting exoplanets.
![Animated cartoon image of a planet crossing in front of a star and an inset that shows a graph dipping as the planet does so](https://www.jpl.nasa.gov/edu/images/activities/piday2018_exoplanet.gif)
This animation shows one method scientists use to hunt for planets outside our solar system. When exoplanets transit their parent star, we can detect the dip in the star’s brightness using space telescopes. Credit: NASA/JPL-Caltech | + Expand image
Additionally, scientists have been exploring the atmospheres of exoplanets. Similarly to how we study Mercury’s exosphere, scientists can observe the spectra – a measure of light intensity and wavelength – that passes through an exoplanet’s atmosphere. As a result, they’re beginning to understand the evolution and composition of exoplanet atmospheres, as well as the influence of stellar wind and magnetic fields.
![Collage of exoplanet posters from NASA](https://www.jpl.nasa.gov/edu/images/news/exo_posters.png)
Using the transit method and other techniques, scientists are learning more and more about planets beyond our solar system. These discoveries have even inspired a series of posters created by artists at NASA, who imagine what future explorers might encounter on these faraway worlds. Credit: NASA | › Download posters
Watch It
During the transit of Mercury, the planet will appear as a tiny dot on the Sun’s surface. To see it, you’ll need a telescope or binoculars outfitted with a special solar filter.
WARNING! Looking at the Sun directly or through a telescope without proper protection can lead to serious and permanent vision damage. Do not look directly at the Sun without a certified solar filter.
The transit of Mercury will be partly or fully visible across much of the globe. However, it won’t be visible from Australia or most of Asia and Alaska.
![Graphic showing Mercury's path across the Sun on Nov. 11, 2019 and the times that it will be at each location](https://www.jpl.nasa.gov/edu/images/news/mercurytransit_2019-crop.png)
The transit of Mercury on Nov. 11, 2019, begins at 4:35 a.m. PST (7:35 a.m. EST), but it won’t be visible to West Coast viewers until after sunrise. Luckily, viewers will have several more hours to take in the stellar show, which lasts until 10:04 a.m. PST (1:04 p.m. EST). Credit: NASA/JPL-Caltech | + Expand image
Mercury’s trek across the Sun begins at 4:35 a.m. PST (7:35 a.m. EST), meaning viewers on the East Coast of the U.S. can experience the entire event, as the Sun will have already risen before the transit begins. By the time the Sun rises on the West Coast, Mercury will have been transiting the Sun for nearly two hours. Fortunately, the planet will take almost 5.5 hours to completely cross the face of the Sun, so there will be plenty of time for West Coast viewers to witness this event. See the transit map below to learn when and where the transit will be visible.
![Graphic showing a flat map of the world with areas where the transit of Mercury on Nov. 11, 2019 will be partially to fully visible indicated along with transit start and end times](https://www.jpl.nasa.gov/edu/images/news/transitmap_2019.jpg)
This map shows where and when the transit will be visible on November 11. Image credit: NASA/JPL-Caltech | + Expand image
Don’t have access to a telescope or binoculars with a solar filter? Visit the Night Sky Network website to find events near you where amateur astronomers will have viewing opportunities available.
During the transit, NASA will share near-real-time images of the Sun directly from the Solar Dynamics Observatory. Beginning at 4:41 a.m. PST (7:41 a.m. EST) you can see images of Mercury passing in front of the Sun at NASA’s 2019 Mercury Transit page, with updates through the end of the transit at 10:04 a.m. PST (1:04 p.m. EST).
If you’re in the U.S., don’t miss the show, as this is the last time a transit will be visible from the continental United States until 2049!
Watch this month's installment of "What's Up" to learn more about how to watch the Nov. 11 transit of Mercury. Credit: NASA/JPL-Caltech | Watch on YouTube
Teach It
Use these lessons and activities to engage students in the transit of Mercury and the hunt for planets beyond our solar system:
-
Exploring Exoplanets with Kepler
Students use math concepts related to transits to discover real-world data about Mercury, Venus and planets outside our solar system.
Grades 6-12
Time 30 mins - 1 hr
-
Sun Screen: A 'Pi in the Sky' Math Challenge
When Mercury passes in front of the Sun, how much sunlight is lost on Earth? Students use the mathematical constant pi to find the solution in this illustrated math challenge.
Grades 6-9
Time < 30 mins
-
Solar Sleuth: A 'Pi in the Sky' Math Challenge
In this illustrated math problem, students use pi and data from the Kepler space telescope to find the size of a planet outside our solar system.
Grades 6-9
Time < 30 mins
-
Can You Spot Mercury?
Play science sleuth and see if you can spot Mercury passing in front of – or transiting – the sun in these images from NASA.
Type Slideshow
Subject Science
-
Oh, the Places We Go: 18 Ways NASA Uses Pi
Whether it's sending spacecraft to other planets, driving rovers on Mars, finding out what planets are made of or how deep alien oceans are, pi takes us far at NASA. Find out how pi helps us explore space.
Type List
Subject Math
Explore More
Transit Resources:
- NASA near-real-time transit images
- Video: What’s Up – November 2019
- 2019 Mercury Transit Map
- Night Sky Network Events
- NASA Museum Alliance Resources
Exoplanet Resources:
- Exoplanet Exploration Website
- Interactive: 5 Ways to Find a Planet
- Interactive: Eyes on Exoplanets
- Posters: Exoplanet Travel Bureau
- Video: What’s in an Exoplanet Name?
- Video: The Search for Another Earth
- Kepler Mission Website
- Kepler Education Activities
Check out these related resources for kids from NASA’s Space Place:
TAGS: K-12 Education, Teachers, Students, Educators, Mercury, Transit, Transit of Mercury, What's Up, Astronomy, Resources for Educators, Exoplanets, Kepler, TESS
Teachable Moments | May 6, 2016
A Teachable Moment You Can See! The Transit of Mercury
UPDATE - May 9, 2016: NASA's Solar Dynamics Observatory, or SDO, spacecraft captured stunning images of the May 9, 2016 transit of Mercury. Visit the mission's Transit of Mercury page to see a collection of videos of the transit compiled using SDO images. And have students play "Can You Spot Mercury?" in our educational slideshow.
In the News
It only happens about 13 times per century and hasn’t happened in nearly a decade, but on Monday, May 9, Mercury will transit the sun. A transit happens when a planet crosses in front of a star. From our perspective on Earth, we only ever see two planets transit the sun: Mercury and Venus. (Transits of Venus are even more rare. The next one won't happen until 2117!) On May 9, as Mercury passes in front of the sun, viewers around Earth (using the proper safety equipment) will be able to see a tiny dark spot moving slowly across the disk of the sun.
CAUTION: Looking directly at the sun can cause permanent vision damage – see below for tips on how to safely view the transit.
Why It's Important
Then and Now
In the early 1600s, Johannes Kepler discovered that both Mercury and Venus would transit the sun in 1631. It was fortunate timing: The telescope had been invented just 23 years earlier and the transits wouldn’t happen in the same year again until 13425. Kepler didn’t survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury (the transit of Venus wasn’t visible from Europe). It was soon understood that transits could be used as an opportunity to measure the apparent diameter – how large a planet appears from Earth – with great accuracy.
In 1677, Edmond Halley observed the transit of Mercury and realized that the parallax shift of the planet – the variation in Mercury’s apparent position against the disk of the sun as seen by observers at distant points on Earth – could be used to accurately measure the distance between the sun and Earth, which wasn’t known at the time.
Today, radar is used to measure the distance between Earth and the sun with greater precision than can be found using transit observations, but the transit of Mercury still provides scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.
Exosphere Science
Some objects, like the moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded in an ultra-thin atmosphere of gases called an exosphere. Scientists want to better understand the composition and density of the gases that make up Mercury’s exosphere and transits make that possible.
“When Mercury is in front of the sun, we can study the exosphere close to the planet,” said NASA scientist Rosemary Killen. “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.”
![Mercury transits the sun in 2006](http://www.jpl.nasa.gov/edu/images/news/transit_mercury-2006.jpg)
Exoplanet Discoveries
When Mercury transits the sun, it causes a slight dip in the sun’s brightness as it blocks a tiny portion of the sun's light. Scientists discovered they could use that phenomenon to search for planets orbiting distant stars, called exoplanets, that are otherwise obscured from view by the light of the star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve (a graph of light intensity) could indicate an exoplanet orbiting and transiting its star. NASA’s Kepler mission has found more than 1,000 exoplanets by looking for this telltale drop in brightness.
![illustration of how transits are used to find exoplanets](http://www.jpl.nasa.gov/edu/images/news/lightcurve_diagram.jpg)
Additionally, scientists have begun exploring the exospheres of exoplanets. By observing the spectra of the light that passes through an exosphere – similar to how we study Mercury’s exosphere – scientists are beginning to understand the evolution of exoplanet atmospheres as well as the influence of stellar wind and magnetic fields.
Watch It
Mercury will appear as a tiny dot on the sun’s surface and will require a telescope or binoculars with a special solar filter to see. Looking at the sun directly or through a telescope without proper protection can lead to serious and permanent vision damage. Do not look directly at the sun without a solar filter.
The transit of Mercury will begin at 4:12 a.m. PDT, meaning by the time the sun rises on the West Coast, Mercury will have been transiting the sun for nearly two hours. Fortunately, it will take seven and a half hours for Mercury to completely cross the sun’s face, so there will be plenty of time for West Coast viewers to witness this event. See the transit map to learn when and where the transit will be visible.
Don’t have access to a telescope, binoculars or a solar filter? Visit the Night Sky Network website for the location of events near you where amateur astronomers will have viewing opportunities available.
NASA also will stream a live program on NASA TV and the agency’s Facebook page from 7:30 to 8:30 a.m. PDT (10:30 to 11:30 a.m. EDT) -- an informal roundtable during which experts representing planetary, heliophysics and astrophysics will discuss the science behind the Mercury transit. Viewers can ask questions via Facebook and Twitter using #AskNASA.
Teach It
Here are two ways to turn the transit of Mercury into a lesson for students.
- Exploring Exoplanets with Kepler - Students use math concepts related to transits to discover real-world data about Mercury, Venus and planets outside our solar system.
- Pi in the Sky 3 - Try the "Sun Screen" problem on this illustrated math problem set that has students calculate the percentage drop in sunlight reaching Earth when Mercury transits.
Explore More
Transit Resources:
- NASA TV (live transit coverage)
- Night Sky Network Events
- Video: What’s Up – May 2016
- Transit Map
- What's a Transit?
- NASA Museum Alliance Resources
Exoplanet Resources:
- Kepler Mission Website
- Exoplanet Exploration Website
- Eyes on Exoplanets Interactive
- Transit Method for Detecting Exoplanets
- Exoplanet Travel Bureau Posters
- Video: What’s in an Exoplanet Name?
- Video: The Search for Another Earth
TAGS: Transit, Transit of Mercury, Mercury, Venus, Sun, Exoplanets, Teach, Classroom Activities, Lessons,