There’s no better time to learn about the Moon than during a lunar eclipse. Here’s how to get students watching and exploring more.
This article has been updated to include information about the visibility and timing of the total lunar eclipse on May 26, 2021. See the "What to Expect" section below for details.
A full moon is always a good reason to go outside and look up, but a total or partial lunar eclipse is an awe-inspiring sight that gives students a great opportunity to engage in practical sky watching. Whether it’s the Moon's reddish hue during a total lunar eclipse or the "bite" taken out of the Moon during a partial lunar eclipse, there's always something exciting to observe during these celestial events. Read on to see what to expect during the next lunar eclipse. Plus, explore resources you can use at home or in the classroom to teach students about moon phases, craters, and more!
How It Works
Eclipses can occur when the Sun, the Moon, and Earth align. Lunar eclipses can only happen during the full moon phase, when the Moon and the Sun are on opposite sides of Earth. At that point, the Moon could move into the shadow cast by Earth, resulting in a lunar eclipse. However, most of the time, the Moon’s slightly tilted orbit brings it above or below the shadow of Earth.
The time period when the Moon, Earth, and the Sun are lined up and on the same plane – allowing for the Moon to pass through Earth’s shadow – is called an eclipse season. Eclipse seasons last about 34 days and occur just shy of every six months. When a full moon occurs during an eclipse season, the Moon travels through Earth’s shadow, creating a lunar eclipse.
Unlike solar eclipses, which require special glasses to view and can only be seen for a few short minutes in a very limited area, a total lunar eclipse can be seen for up to an hour by anyone on the nighttime side of Earth – as long as skies are clear!
Why It’s Important
Lunar eclipses have long played an important role in understanding Earth and its motions in space.
In ancient Greece, Aristotle noted that the shadows on the Moon during lunar eclipses were round, regardless of where an observer saw them. He realized that only if Earth were a spheroid would its shadows be round – a revelation that he and others had many centuries before the first ships sailed around the world.
Earth wobbles on its axis like a spinning top that’s about to fall over, a phenomenon called precession. Earth completes one wobble, or precession cycle, over the course of 26,000 years. Greek astronomer Hipparchus made this discovery by comparing the position of stars relative to the Sun during a lunar eclipse to those recorded hundreds of years earlier. A lunar eclipse allowed him to see the stars and know exactly where the Sun was for comparison – directly opposite the Moon. If Earth didn’t wobble, the stars would appear to be in the same place they were hundreds of years earlier. When Hipparchus saw that the stars’ positions had indeed moved, he knew that Earth must wobble on its axis!
Additionally, modern-day astronomers have used ancient eclipse records and compared them with computer simulations. These comparisons helped scientists determine the rate at which Earth’s rotation is slowing.
What to Expect
The Moon passes through two distinct parts of Earth’s shadow during a lunar eclipse. The outer part of the cone-shaped shadow is called the penumbra. The penumbra is less dark than the inner part of the shadow because it’s penetrated by some sunlight. (You have probably noticed that some shadows on the ground are darker than others, depending on how much outside light enters the shadow; the same is true for the outer part of Earth’s shadow). The inner part of the shadow, known as the umbra, is much darker because Earth blocks additional sunlight from entering the umbra.
Here's what to expect during the total lunar eclipse on May 26, 2021, which will be visible in western North and South America, as well as in eastern Asia, Australia, and the Pacific Ocean. Note: Viewers in the Midwest and the eastern U.S. can still look up to see a partial eclipse grace the sky.
At 1:47 a.m. PDT, the edge of the Moon will begin entering the penumbra. The Moon will dim very slightly for the next 57 minutes as it moves deeper into the penumbra. Because this part of Earth’s shadow is not fully dark, you may only notice some dim shading (if anything at all) on the Moon near the end of this part of the eclipse. Should you decide to sleep in during this time, you won’t miss much.
At 2:45 a.m. PDT, the edge of the Moon will begin entering the umbra. As the Moon moves into the darker shadow, significant darkening will be noticeable. Some say that during this part of the eclipse, the Moon looks as if it has had a bite taken out of it. That “bite” gets bigger and bigger as the Moon moves deeper into the shadow. During this part, viewers in most of the eastern U.S. will see the Moon as it moves into the umbra but lose visibility once the Moon dips below the horizon and the Sun rises.
At 4:11 a.m. PDT, the Moon will be completely inside the umbra, marking the beginning of the total lunar eclipse. The moment of greatest eclipse, when the Moon is halfway through its path across the umbra, occurs at 4:19 a.m. PDT.
As the Moon moves completely into the umbra, something interesting happens: The Moon begins to turn reddish-orange. The reason for this phenomenon? Earth’s atmosphere. As sunlight passes through it, the small molecules that make up our atmosphere scatter blue light, which is why the sky appears blue. This leaves behind mostly red light that bends, or refracts, into Earth’s shadow. We can see the red light during an eclipse as it falls onto the Moon in Earth’s shadow. This same effect is what gives sunrises and sunsets a reddish-orange color.
A variety of factors affect the appearance of the Moon during a total lunar eclipse. Clouds, dust, ash, photochemical droplets, and organic material in the atmosphere can change how much light is refracted into the umbra. Additionally, the May 2021 lunar eclipse takes place when the full moon is at or near the closest point in its orbit to Earth (popularly known as a supermoon). This means it is deeper inside the umbra shadow and therefore may appear darker. The potential for variation provides a great opportunity for students to observe and classify the lunar eclipse based on its brightness. Details can be found below in the “Teach It” section.
At 4:25 a.m. PDT, the edge of the Moon will begin exiting the umbra and moving into the opposite side of the penumbra. This marks the end of the total lunar eclipse.
At 5:52 a.m. PDT, the Moon will be completely outside of the umbra and will begin exiting the penumbra until the eclipse ends at 6:49 a.m. PDT.
Ask students to observe the lunar eclipse and evaluate the Moon’s brightness using the Danjon Scale of Lunar Eclipse Brightness. The Danjon scale illustrates the range of colors and brightness the Moon can take on during a total lunar eclipse and is a tool observers can use to characterize the appearance of an eclipse. View the lesson guide here. After the eclipse, have students compare and justify their evaluations of the eclipse.
Use these standards-aligned lessons and related activities to get your students excited about the eclipse, moon phases, and Moon observations.
Educator Guides & Resources
Evaluating a Lunar Eclipse
Students use the Danjon Scale of Lunar Eclipse Brightness to illustrate the range of colors and brightness the Moon can take on during a total lunar eclipse.
Time 30 mins - 1 hr
When Do Lunar Eclipses Happen?
Students use a paper plate to make a model that explains why lunar eclipses don’t occur during every full moon.
Time Less than 30 mins
Observing the Moon
Students identify the Moon’s location in the sky and record their observations over the course of the moon-phase cycle in a journal.
Time 30 mins - 1 hr
Students learn about the phases of the moon by acting them out.
Time 30 mins - 1 hr
Whip Up a Moon-Like Crater
Whip up a moon-like crater with baking ingredients as a demonstration for students.
Time 30 mins - 1 hr
Modeling the Earth-Moon System
Students learn about scale models and distance by creating a classroom-size Earth-Moon system.
Time 30 mins - 1 hr
Teachable Moment: What’s a Supermoon and Just How Super Is It?
Are supermoons as super as they're made out to be? Learn what causes them and explore related activities for teachers and students.
Measuring the Supermoon
Students use analog and digital tools to measure the Moon’s apparent size and brightness.
Time 30 mins - 1 hr
All Moon Lessons for Educators
Teach students all about the Moon with these standards-aligned STEM lessons for educators.
When Do Lunar Eclipses Happen?
Use a paper plate to make a model that explains why lunar eclipses don’t happen as often as you might expect.
Make a Moon Phases Calendar and Calculator
Like a decoder wheel for the Moon, this calendar will show you where and when to see the Moon and every moon phase throughout the year!
Look at the Moon! Journaling Project
Draw what you see in a Moon Journal and see if you can predict the moon phase that comes next.
Make a Moon Crater
Make craters like the ones you can see on the Moon using simple baking ingredients!
All Moon Activities for Students
Make a moon phases calendar, moon crater, lunar rover and more with these activities all about Earth's moon.
- Try these related resources for students from NASA's Space Place:
- Article for Kids: Lunar Eclipses and Solar Eclipses
- Article for Kids: Why Does the Moon Have Craters?
- Article for Kids: All About the Moon
- NASA Moon Website – Find out more about the Moon and the NASA robots and humans who have visited it.
Lina Khosrovian is a first-year teacher at Stonehurst Magnet Elementary, a STEAM magnet school in Los Angeles County. She teaches third-grade students subjects including language arts, math, science and social studies. Ms. Khosrovian recently reached out about how she added her own creative spin to the JPL lesson Art and the Cosmic Connection to have it reflect her multidisciplinary classroom.
What inspires you to teach?
I am in my first year of teaching, and I could not be more driven and excited to teach my students about all the wonders of life. I am a learner myself, and I strive to discover new and moving ways to instill knowledge upon my students.
I consider myself extremely lucky to be teaching at Stonehurst, where we have a passion for teaching STEAM to our students. I especially appreciate the students’ enthusiasm for learning science.
What challenges do you face engaging or addressing the needs of your students?
I have found that the key to effectively and successfully teaching students is to teach what they admire, are curious or fascinated about or have an appreciation for. I always ask my students about their interests and what they would like to learn. This inspires my lessons and tends to each students’ individual interest in learning.
How did you incorporate a JPL Education lesson into your classroom?
Art and the Cosmic Connection
In this lesson for grades K-12, students use art to describe and recognize the geology on planetary surfaces.
Brandon Rodriguez, an educator professional development specialist at NASA’s Jet Propulsion Laboratory, visited our school and presented a lesson called Art and the Cosmic Connection.
After showing us images of planets, Mr. Rodriguez handed out paper, chalk, crayons and markers, and instructed us to draw our own imaginary planet. Listening to his awe-inspiring lecture, I began to think about the beautiful garden at our school and wondered how I could incorporate it into a similar activity with my students. I decided that I would have my students create their own planet inspired by the school garden.
First, my students and I began to learn about different planets together, discussing the possible history of each unique world. We conversed and wrote about our theories. Then each student drew and wrote about their own, imaginary planet. Some students drew icy planets and said that the ice had melted when the planet was close to the Sun. Other students explained that the uniqueness of their planet was due to the presence of life and water.
With our knowledge, ideas and imagination, we grabbed paper bags to collect soil, sticks, hay, leaves, rocks and other natural items from the garden. Back in the classroom, each student began to construct 3-D versions of their drawings with the materials they collected. Their work was beautifully presented, with soil representing land, leaves representing life, blue paint representing water, and mixtures representing unknown and unique creations – plus some silver paint to make it all more “cosmic.”
How did it help you meet your objectives? How did students react to the lesson?
This lesson allowed my students to engage with the world around them and understand that planets have a uniqueness and a history that is quite remarkable. The lesson gave students a chance to discover more about their own planet and express their connection to it.
I sincerely value the JPL Education lessons, activities and resources, as they are quite beneficial to teachers. Each activity and lesson provides the opportunity for students to learn and wonder. And when you’re inspired to wonder, the possibilities are endless – and so is the fun!
Looking for ways to bring NASA STEM into your classroom or already have a great idea? The Education Office at NASA's Jet Propulsion Laboratory serves educators in the greater Los Angeles area. Contact us at email@example.com.
Try this lesson from NASA/JPL Edu to get involved and bring the excitement of NASA Mars exploration to students:
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.
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.”
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.
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.
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.
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.
- NASA TV (live transit coverage)
- NASA Transit Website (near real-time images of the transit)
- Night Sky Network Events
- Video: What’s Up – May 2016
- Transit Map
- Solar System Transits
- NASA Museum Alliance Resources
- Kepler Mission Website
- Exoplanet Exploration Website
- Eyes on Exoplanets Interactive
- Exoplanet Travel Bureau Posters
- Video: What’s in an Exoplanet Name?
- Video: The Search for Another Earth
- Kepler Education Activities
In the News
Twenty years after the first discovery of a planet orbiting another sun-like star, scientists have discovered the most Earth-like exoplanet ever: Kepler-452b. Located in the habitable zone of a star very much like our sun, Kepler-452b is only about 60 percent wider than Earth.
What makes it the most Earth-like exoplanet ever discovered?
First a couple definitions: An exoplanet is simply a planet that orbits another star. And the habitable zone? That’s the area around a star in which water has the potential to be liquid -- not so close to the star that all water would evaporate, and not so far that all water would freeze. Think about Goldilocks eating porridge. The habitable zone is not too hot, and not too cold. It’s just right.
Okay, back to Kepler-452b. Out of more than a thousand exoplanets that NASA’s Kepler spacecraft has detected, only 12 have been found in the habitable zone of their stars and are smaller than twice the size of Earth, making Earth-like planets a rarity. Until this discovery, all of them have orbited stars that are smaller and cooler than our sun.
Kepler-452b is the first to be discovered orbiting a star that is about the same size and temperature as our sun. Not only that, but it orbits at nearly the same distance from its star as Earth does from our sun! Conditions on Kepler-452b could be similar to conditions here on Earth and the light you would feel there would be much like the sunlight you feel here on Earth. Scientists believe that Kepler-452b has been in the habitable zone for around six billion years -- longer than Earth has even existed!
How They Did It
The Kepler spacecraft, named for mathematician and astronomer Johannes Kepler, has been working since 2009 to find distant worlds like Kepler-452b. It does so by looking at more than 100,000 stars near the constellation Cygnus. If one of those stars dims temporarily, it could be that an object passed between the spacecraft and the star. If it dims with a repeatable pattern, there’s a good chance an exoplanet is passing by again and again as it orbits the star. The repeated dimming around one of those stars is what led to the discovery of Kepler-452b.
This exciting discovery provides opportunities for students to practice math skills in upper elementary and middle school, and gives high school students a practical application of Kepler’s third law of planetary motion. Take a look below to see where these might fit into your curriculum.
Upper Elementary and Middle School
After learning about Earth’s cousin, students might wonder about a trip to this world. Scientists have calculated the distance between Earth and Kepler-452b at 1,400 light years. A light year is a measure of distance that shows how far light travels in one year. It’s equal to about 10 trillion kilometers (six trillion miles) or, to be more precise, 9,461,000,000,000 kilometers (5,878,000,000,000 miles). Ask students to calculate the distance between Earth and Kepler-452b at various levels of precision, depending on what they are prepared for or learning. For an added challenge, have them determine how long it would take a fast moving spacecraft like Voyager 1 traveling at 61,000 kph (38,000 mph) to reach this new world.
Note: Due to the approximations of spacecraft speed and light year distance used for these problems in both standard and metric units, there is a variation among the answers.
Distance: 10 trillion km x 1,400 = 14,000 trillion km (that’s 14,000,000,000,000,000 kilometers!)
Travel time: 14,000 trillion km ÷ 61,000 kph ÷ 24 ÷ 365 ≈ 26,000,000 years
Distance: 6 trillion miles x 1,400 = 8,400 trillion miles (that’s 8,400,000,000,000,000 miles!)
Travel time: 8,400 trillion miles ÷ 38,000 mph ÷ 24 ÷ 365 ≈ 25,000,000 years
or more precisely…
Distance: 9,461,000,000,000 km x 1,400 = 13,245,400,000,000,000 km
Travel time: 13,245,400,000,000,000 km ÷ 61,000 kph ÷ 24 ÷ 365 ≈ 25,000,000 years
Distance: 5,878,000,000,000 miles x 1,400 = 8,229,200,000,000,000 miles
Travel time: 8,229,200,000,000,000 miles ÷ 38,000 mph ÷ 24 ÷ 365 ≈ 25,000,000 years
or using exponents and powers of 10…
Distance: 9.461 x 1012 x km x 1.4 x 103 = 1.32454 x 1016 km
Travel time: 1.32454 x 1016 km ÷ 6.1 x 104 kph ÷ 2.4 x 101 ÷ 3.65 x 102 ≈ 2.5 x 107 years
Distance: 5.878 x 1012 miles x 1.4 x 103 = 8.2292 x 1015 miles
Travel time: 8.2292 x 1015 miles ÷ 3.8 x 104 mph ÷ 2.4 x 101 ÷ 3.65 x 102 ≈ 2.5 x 107 years
Middle and High School
The time between detected periods of dimming, the duration of the dimming, and the amount of dimming, combined with a little math, can be used to calculate a great deal of information about an exoplanet, such as the length of its orbital period (year), the distance from its star, and its size.
Kepler-452b has an orbital period of 384.84 days -- very similar to Earth’s 365.25 days. Students can use the orbital period to find the distance from its star in astronomical units. An astronomical unit is the average distance between Earth and our Sun, about 150 million kilometers (93 million miles).
Kepler’s 3rd law states that the square of the orbital period is proportional to the cube of the semi-major axis of an ellipse about the sun. For planets orbiting other stars, we can use R = ∛(T2 ∙ Ms) where R = semi-major axis, T = orbital period in Earth years, and Ms = the mass of the star relative to our sun (the star that Kepler-452b orbits has been measured to be 1.037 times the mass of our sun).
T = 384.84 ÷ 365.25 = 1.05
R = ∛(1.052 ∙ 1.037)
R = ∛1.143 = 1.05 AU
- Exoplanet Travel Bureau Posters
- Video: What’s a “habitable zone?”
- Video: What’s in an Exoplanet Name?
Facts and Figures