Animation showing a total lunar eclipse. Credit: NASA Goddard Media Studios

In the News

A full moon is always a good reason to go outside and turn your head toward the sky, but those who do so early on January 31 will be treated to the sight of what’s being called the super blue blood moon! Super, because the moon will be closest to Earth in its orbit during the full moon (more on supermoons here); blue, because it’s the second full moon in a calendar month; and blood, because there will be a total lunar eclipse that will turn the moon a reddish hue. It’s the only total lunar eclipse (blood moon) visible from North America in 2018, so it’s a great opportunity for students to observe the Moon – and for teachers to make connections to in-class science content.

How It Works

Side-by-side images showing how the Moon, Sun and Earth align during an lunar eclipse versus a standard full moon

These side-by-side graphics show how the Moon, Sun and Earth align during a lunar eclipse (left) versus a non-eclipse full moon (right). Credit: NASA Goddard Visualization Studio | + Enlarge image

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.

Graphic showing the alignment of the Sun, Earth and Moon when a full moon occurs during an eclipse season versus a non-eclipse season

When a full moon occurs during an eclipse season, the Moon travels through Earth's shadow, creating a lunar eclipse. Credit: NASA/JPL-Caltech | + Enlarge image

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 about an hour by anyone on the nighttime side of Earth – as long as skies are clear!

Why It’s Important

Moon and Supermoon Lessons from NASA/JPL Edu

Lessons About the Moon

Explore our collection of standards-aligned lessons for grades 1-12.

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

Graphic showing the positions of the Moon, Earth and Sun during a partial lunar eclipse

During a total lunar eclipse, the Moon first enters into the penumbra, or the outer part of Earth's shadow, where the shadow is still penetrated by some sunlight. Credit: NASA | + Enlarge image

The Moon as seen during a partial lunar eclipse

As the Moon starts to enter into the umbra, the inner and darker part of Earth's shadow, it appears as if a bite has been taken out of the Moon. This "bite" will grow until the Moon has entered fully into the umbra. Credit: NASA | + Enlarge image

Graphic showing the Moon inside the umbra

The total lunar eclipse starts once the moon is completely inside the umbra. And the moment of greatest eclipse happens with the Moon is halfway through the umbra as shown in this graphic. Credit: NASA | + Enlarge image

The Moon as seen during a total lunar eclipse at the point of greatest eclipse

As the Moon moves completely into the umbra, it turns a reddish-orange color. Credit: NASA | + Enlarge image

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.

At 2:51 a.m. PST on January 31, 2018, 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 3:48 a.m. PST, 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. If you will be on the East Coast of the United States, you might still be able to see the Moon just as it moves into the umbra before the Moon sets and the Sun rises.

At 4:51 a.m. PST, 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 the umbra, occurs at 5:31 a.m. PST.

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 January 2018 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 6:07 a.m. PST, 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 7:11 a.m. PST, the Moon will be completely outside of the umbra. It will continue moving out of the penumbra until the eclipse ends at 8:08 a.m.

Teach It

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.

  • *NEW* Evaluating a Lunar Eclipse (Grades 3-12) - 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.
  • Observing the Moon (Grades K-6) - Students identify the Moon’s location in the sky and record their observations in a journal over the course of the moon-phase cycle.
  • Moon Phases (Grades 1-6) - Students learn about the phases of the Moon by acting them out. In 30 minutes, they will act out one complete, 30-day, Moon cycle.
  • Measuring the Supermoon (Grades 5-12) - Students take measurements of the Moon during its full phase over multiple Moon cycles to compare and contrast results.
  • Modeling the Earth-Moon System (Grades 6-8) – Students learn about scale models and distance by creating a classroom-size Earth-Moon system.
  • 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!

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TAGS: Lunar Eclipse, Moon, Super Blue Blood Moon, Observe the Moon, Eclipse, K-12, Classroom Activities, Teaching

  • Lyle Tavernier
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Update – Aug. 17, 2017: Two new lessons ("Measuring Solar Energy During an Eclipse" and "Modeling the Earth-Moon System") were added to the Teach It section below.


In the News

A satellite image of the Moon's shadow on Earth during a total solar eclipse

The Moon casts a shadow on Earth during a total solar eclipse over Europe in this image taken by a French astronaut on the Mir Space Station. Credit: CNES

This month marks the first time in 38 years that one of nature’s most awe-inspiring sights, a total solar eclipse, will be visible from the continental United States. And unlike the 1979 eclipse, the one on August 21 can be seen from coast to coast – something that hasn’t happened since 1918.

Millions of people are expected to travel to the 14 states that are in the path of totality – where the Moon will completely cover the disk of the Sun – while hundreds of millions more in every other state of the U.S. will be able to see a partial eclipse.

Whether you live in or are traveling to the path of totality, or will be able to step outside and view the partial eclipse from the comfort of your own home or school, the eclipse provides both an inspiring reason to look to the sky and opportunities to engage in scientific observations and discovery.

Animation of the Aug. 21, 2017 eclipse – Pi in the Sky 4 math problem

Teach It

Use these standards-aligned lessons and related activities to get your students excited about the eclipse and the science that will be conducted during the eclipse.

› Get started!

How it Works

Eclipses occur as the result of an alignment between the Sun, the Moon and Earth. Solar eclipses can only happen during the new moon phase, when the Moon’s orbit brings it between Earth and the Sun. At this time, the shadow cast by the moon could land on Earth, resulting in an eclipse. But most of the time, because the moon’s orbit is slightly titled, the moon’s shadow falls above or below Earth.

The time period when the Moon, Earth and the Sun are lined up and on the same plane is called an eclipse season. Eclipse seasons last about 34 days and occur just shy of every six months. A new moon during an eclipse season will cause the Moon’s shadow to fall on Earth, creating a solar eclipse.

graphic showing eclipse seasons
An eclipse season is the time period when the Moon, Earth and the Sun are lined up on the same plane. A new moon during an eclipse season will cause the Moon's shadow to fall on Earth, creating a solar eclipse. Image credit: NASA/JPL-Caltech

In addition to the proper alignment required for an eclipse, the distance between Earth, the Moon and the Sun also plays an important role. Even though the Moon is much smaller than the Sun (about 400 times smaller in diameter), the Sun and Moon appear about the same size from Earth because the Sun is about 400 times farther away than the Moon. If the Moon were farther from Earth, it would appear smaller and not cover the disk of the Sun. Similarly, if the Sun were closer to Earth, it would appear larger and the Moon would not completely cover it.

Why It’s Important

Total solar eclipses provide a unique opportunity for scientists to study the Sun and Earth from land, air and space, and allow the public to engage in citizen science!

Total eclipse image taken March 20, 2015 in Svalbard, Norway. Credit: S. Habbal, M. Druckmüller and P. Aniol

The sun's outer atmosphere (corona) and thin lower atmosphere (chromosphere) can be seen streaming out from the covered disk of the sun during a solar eclipse on March 20, 2015. Credit: S. Habbal, M. Druckmüller and P. Aniol

On a typical day, the bright surface of the Sun, called the photosphere, is the only part of the Sun we can see. During a total solar eclipse, the photosphere is completely blocked by the Moon, leaving the outer atmosphere of the Sun (corona) and the thin lower atmosphere (chromosphere) visible. Studying these regions of the Sun’s atmosphere can help scientists understand solar radiation, why the corona is hotter than the photosphere, and the process by which the Sun sends a steady stream of material and radiation into space.

Scientists measure incoming solar radiation on Earth, also known as insolation, to better understand Earth’s radiation budget – the energy emitted, reflected and absorbed by Earth. Just as clouds block sunlight and reduce insolation, the eclipse will block sunlight, providing a great opportunity to study how increased cloud cover can impact weather and climate. (Learn more about insolation during the 2017 eclipse here.)

Citizen scientists can get involved in collecting data and participating in the scientific process, too, through NASA’s Global Learning and Observations to Benefit the Environment, or GLOBE, program. During the eclipse, citizen scientists in the path of totality and in partial eclipse areas can measure temperature and cloud cover data and report it using the GLOBE Observer app to help further the study of how eclipses affect Earth’s atmosphere.

You can learn more about the many ways scientists are using the eclipse to improve their understanding of Earth, the Moon and the Sun here.

How to View It

Important! Do not look directly at the Sun or view the partial eclipse without certified eclipse glasses or a solar filter. For more information on safe eclipse viewing, visit the NASA Eclipse website.

When following proper safety guidelines, witnessing an eclipse is an unparalleled experience. Many “eclipse chasers” have been known to travel the world to see total eclipses.

The start time of the partial eclipse, when the edge of the Moon first crosses in front of the disk of the Sun, will depend on your location. You can click on your location in this interactive eclipse map to create a pin, which will show you the start and end time for the eclipse in Universal Time. (To convert from Universal Time to your local time, subtract four hours for EDT, five hours for CDT, six hours for MDT, or seven hours for PDT.) Clicking on your location pin will also show you the percent of Sun that will be eclipsed in your area if you’re outside the path of totality.

Aug 2017 eclipse map
This graphic shows the path of the Moon and Sun across the US during the Aug. 21, 2017 eclipse. The gray line represents the path of totality, while the Sun and Moon graphics flowing from top to bottom represent the percent of coverage for areas outside the path of totality. Image credit: NASA

If you are inside the approximately 70-mile-wide strip known as the path of totality, where the shadow of the Moon, or umbra, will fall on Earth, the total eclipse will be visible starting about an hour to 1.5 hours after the partial eclipse begins.

Only when the eclipse is at totality – and the viewer is in the path of totality – can eclipse glasses be removed. Look at the eclipse for anywhere from a few seconds to more than 2.5 minutes to see the Sun’s corona and chromosphere, as well as the darkened near side of the Moon facing Earth. As before, your viewing location during the eclipse will determine how long you can see the eclipse in totality.

graphic showing when its safe to remove your eclipse glasses if you are in the path of totality
Viewers should wear eclipse glasses or use a pinhole camera for the entirety of the partial eclipse. Those in the path of totality can remove their glasses only when the eclipse is in totality, which may last from a few seconds to more than 2.5 minutes depending on your location. Image credit: NASA

After totality ends, a partial eclipse will continue for an hour to 1.5 hours, ending when the edge of the Moon moves off of the disk of the Sun. Remember, wear eclipse glasses or use a pinhole camera for the entirety of the partial eclipse. Do not directly view the partial eclipse.

Animation of the pinhole camera project from NASA-JPL Education

Make a Pinhole Camera

Find out how to make your very own pinhole camera to safely view the eclipse in action.

› Get started!

To get an idea of what the eclipse will look like from your location and explore the positions of the Moon, Sun and Earth throughout the eclipse, see this interactive simulation.

For more information about the start of the partial eclipse, the start and duration of totality, and the percentage of the Sun eclipsed outside the path of totality, find your location on this interactive eclipse map.

NASA Television will host a live broadcast beginning at 9 a.m. PDT on Aug. 21 showing the path of totality and featuring views from agency research aircraft, high-altitude balloons, satellites and specially-modified telescopes. Find out how and where to watch, here

Teach It

Use these standards-aligned lessons and related activities to get your students excited about the eclipse and the science that will be conducted during the eclipse.

  • Epic Eclipse – Students use the mathematical constant pi to approximate the area of land covered by the Moon’s shadow during the eclipse.
  • Pinhole Camera – Learn how to make your very own pinhole camera to safely see a solar eclipse in action from anywhere the eclipse is visible, partial or full!
  • Moon Phases - Students learn about the phases of the Moon by acting them out. In 30 minutes, they will act out one complete, 30-day, Moon cycle.
  • NEW! Measuring Solar Energy During an Eclipse – Students use mobile devices to measure the impact a solar eclipse has on the energy received at Earth’s surface.
  • NEW! Modeling the Earth-Moon System – Students learn about scale models and distance by creating a classroom-size Earth-Moon system.
  • NASA GLOBE Observer – Students can become citizen scientists and collect data for NASA’s GLOBE Program using this app available for iOS and Android devices (eclipse update available starting August 18, 2017).

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TAGS: Eclipse, Solar Eclipse, Science, Pinhole Camera, K-12, Students, Educators

  • Lyle Tavernier
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