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This story appears in the August 2017 issue ofNational Geographic magazine.

On August 21, 2017, the moon will cast a shadow that will take a little over an hour and a half to traverse North America, plunging some areas into darkness for as much as two minutes, 41 seconds.

Total solar eclipses occur only when the moon is directly between the Earth and the sun-a rare occasion given the moon's slightly tilted orbit. This summer's eclipse -stretching from Salem, Oregon, to Charleston, South Carolina-will be the first total solar eclipse visible in the continental U.S. in 38 years.

But be advised: Never look directly at the sun except during totality, in the umbra, without proper eye protection.

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Map Reveals How to See 2017's Incredible Total Solar Eclipse

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This story appears in the August 2017 issue ofNational Geographic magazine. On August 21, 2017, the moon will cast a shadow that will take a little over an hour and a half to traverse North America, plunging some areas into darkness for as much as two minutes, 41 seconds.

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national aeronautics and space administration

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Total Solar Eclipse 2017 - On Monday, August 21, 2017, all of North America will be treated to an eclipse of the sun. Anyone within the path of totality can see one of nature's most awe inspiring sights - a total solar eclipse.

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Total Solar Eclipse on August 21, 2017 (Great American Eclipse)

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The total eclipse on Monday, August 21, 2017 - Are you able to see it?

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Eclipses visible in San Diego, California, USA - Aug 21, 2017 Solar Eclipse

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Which upcoming lunar and solar eclipses are visible in San Diego, California, USA and what do they look like?

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The dark oval represents where totality will be seen at that moment. The time of eclipse is given in the local time zone. The duration is the maximum at the center of the Moon's shadow. Places near the centerline receive the longest duration.

The path narrows throughout North America because after the Moon's shadow meets the point of greatest eclipse near Nazas, Mexico, the distance from the Moon to the Earth becomes slightly longer. While the path is narrowing, the shadow is also intercepting the Earth's surface at an increasingly oblique angle. This oblique angle lengthens the shadow along the direction of the path. So this results in the shadow becoming narrower as the eclipse moves from Texas to Newfoundland while also elongating the shape of the shadow.

To see the full glory of a total solar eclipse, when daylight suddenly darkens and the beautiful corona of the Sun becomes visible, people must be inside the inner shadow of the Moon (called the umbra). Even if people are in the zone of 99% partial solar eclipse, they will experience 0% total solar eclipse. Being inside the path is essential to view totality.

Experience nature's greatest sight - a total eclipse of the Sun! On April 8, 2024, the shadow of the Moon will cross Mexico, the United States, and Canada. This spectacular total solar eclipse will amaze many millions of people. This is sure to be a record-setting astronomical event.

Before that, the US is lucky to have a celestial warm-up act - an annular solar eclipse from Oregon to Texas on October 14, 2023.

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A total solar eclipse is coming to America on April 8, 2024. Find maps, videos, how to view, best places to go, eclipse glasses, and more.

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Safe Viewing Techniques | How to View an Eclipse | Exploratorium

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There are many ways that you can safely enjoy a partial or total solar eclipse using items from around your house! Dr. Paul Doherty will show you a few of the easiest methods for safe solar viewing. Let us make this perfectly clear: Don't EVER look directly at the sun, even when it's mostly covered during a solar eclipse.

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Activities and Resources

AWB's unique program uses the upcoming eclipse as the starting point for continuing STEM education lessons and activities. to be conducted in the following academic year. Astronomy Without Borders New Building on Eclipse Education Program
Register today.

Night Sky Network Eclipse 2017 Resources
FAQs, activities, and other eclipse-related resources, including an editable postcard to distribute in your community.

Big Kid Science Eclipse Page
Videos from author Jeffrey Bennett to help you enjoy and understand the eclipse.

ASP and NSTA Eclipse Articles

Enjoy complimentary access to over 15 articles on Solar Eclipses from Mercury, our membership-only magazine.

The Universe in the Classroom
Getting Ready for the All American Eclipse! An NGSS Storyline Approach to Classroom Instruction by Brian Kruse

NSTA Science Scope, Science & Children, and The Science Teacher
( Free PDF files to download and share)

An Observer's Guide to Viewing the Eclipse
Author's Andrew Fraknoi and Dennis Schatz share an excerpt, from their book Solar Science. The complete book is available in the ASP's AstroShop.

Events

Help Create the Eclipse Megamovie!
In partnership with Google, UC Berkeley and seven other organizations, the ASP is helping to create the Eclipse Megamovie 2017! The ASP is recruiting and training skilled photographers so if you wish to participate, SIGN IN to apply!

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AWB's unique program uses the upcoming eclipse as the starting point for continuing STEM education lessons and activities. to be conducted in the following academic year. Astronomy Without Borders New Building on Eclipse Education Program Register today. Night Sky Network Eclipse 2017 Resources FAQs, activities, and other eclipse-related resources, including an editable postcard to distribute in your community.

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Science Teaching Materials - NSTA Press Extras: Solar Science

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On their journey through space, the Earth and the Moon cast 3 different shadows causing different types of solar and lunar eclipses. Why are there 3 shadows?

Eclipse Type Depends on Shadow Type

If the Moon's shadow falls on Earth, we get to see a solar eclipse; the Earth's shadow falling on the Moon results in a lunar eclipse. However, there are different types of solar and lunar eclipses. A solar eclipse may be total, partial, or annular; a lunar eclipse may be total, partial, or penumbral.

The type of eclipse we experience depends on the type of shadow that is involved. Both the Moon and Earth cast 3 shadows:

The umbra is the shadow's dark center portion, while the penumbra and the antumbra are different types of half-shadows.

Shadow Experiments

To understand why the Earth and the Moon have 3 types of shadows, let's start on a smaller scale. The number and types of shadows created by an opaque object depend on its size in relation to the size of the light source. However, their absolute size is irrelevant, so a basketball illuminated by a large lamp produces the same shadows as the Moon illuminated by the Sun.

So imagine that you are in a windowless room with 1 light source and 1 round object that casts a shadow, say, a basketball. Both the light source and the basketball are at the same height as your head. You are standing on the side of the ball exactly opposite to the light source, facing it, so the order is: light source - basketball - you.

1st Experiment: Umbra Only
Rule: If the light emanates from a punctual light source, the object casts only 1 type of shadow: an umbra.
Let's say the light source is a tiny flashlight pointing into your direction. If you look into the direction of the lamp from behind the basketball, it is entirely invisible as the ball blocks the view and the light rays don't reach you. The ball's shadow is uniform, it only has an umbra.

If you move to the side, the flashlight immediately becomes visible as soon as you leave the shadow.

2nd Experiment: Umbra and Penumbra

Rule: If the light source is not punctual but has a larger surface area, a 2nd type of shadow appears around the object's umbra: the penumbra.
Now the light source is a round lamp that is a little smaller in diameter than the basketball. If you line up with the lamp and the ball, no light is visible because you are within the ball's umbra. However, as you move to either side, part of the light source becomes visible. That's the penumbra.

If you move further to the side until you can see all of the lamp's surface, you have left the penumbra.

3rd Experiment: Umbra, Penumbra, and Antumbra

Rule: If the diameter of the light source is larger than the diameter of the object, a 3rd type of shadow appears where the V-shaped umbra ends: the antumbra.
In this experiment, the light source is another round lamp, but this time it has twice the ball's diameter. Imagine once more that you are looking at the lamp from behind the ball. As long as you are fairly close to it, the ball's apparent size exceeds the lamp's apparent size. You are within the umbra, and the lamp is invisible.

However, as you move away from the ball, its apparent size decreases. At some point, the basketball will appear smaller than the lamp. A ring of light will appear around the ball as the outer rim of the lamp comes into view. You have just entered the basketball's antumbra.

3 Shadows, 6 Types of Eclipses

Our solar system resembles the set-up of the last experiment. The Sun is a very large light source, its diameter exceeding that of both the Earth and the Moon. This means that, on their journey through space, both objects produce all 3 types of shadows.

Depending on which shadow type is involved, we can experience 3 different types of solar eclipses and 3 different types of lunar eclipses on Earth:

Umbra Eclipses

The umbral shadow can produce the following eclipses:

Penumbra Eclipses

The penumbral shadow is involved in these eclipses:

Partial solar eclipse - the Moon's penumbra falls on the Earth's surface, and the observer is within the penumbra.

Partial lunar eclipse - the Earth's penumbra covers the area of the Moon's visible surface that is not covered by the umbra.

Penumbral lunar eclipse - the penumbra covers all or part of the Moon, the umbra misses it.

Antumbra Eclipses

The antumbral shadow can only cause 1 type of eclipse:

Annular solar eclipse - the Moon's antumbra falls on the Earth's surface, and the observer is within the antumbra.

Topics: Eclipses, Sun, Astronomy, Moon, Earth

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On their journey through space, the Earth and the Moon cast 3 different shadows causing different types of solar and lunar eclipses. Why are there 3 shadows? If the Moon's shadow falls on Earth, we get to see a solar eclipse; the Earth's shadow falling on the Moon results in a lunar eclipse.

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Never look directly at the Sun. You can seriously hurt your eyes, and even go blind. Proper eye protection, like eclipse glasses or a special solar filter, is the only safe option. Sunglasses don't work.

NEWS: Don't miss the 2023 annular solar eclipse
October 14, 2023: Annular Solar Eclipse

On October 14, an annular solar eclipse will sweep across the Americas.

Annularity, where the Sun forms a 'ring of fire' around the Moon, is visible along a narrow path that crosses the USA, Mexico, Central America, Colombia, and Brazil. Elsewhere in the Americas-from Alaska to Argentina-a partial eclipse will be visible.
Watch it LIVE!
How Not to Watch Solar Eclipses

According to NASA, the following materials should never be used to view a solar eclipse:

sunglasses of any kind

color film

medical X-ray film

smoked glass

floppy disks

The Sun can burn the retinas in the eyes leading to permanent damage or even blindness. This can occur even if your eyes are exposed to direct sunlight for just a few seconds.

Safely Watch a Solar Eclipse

The only way to safely view the Sun - eclipsed or not - is to either project or filter the Sun's rays.

Projectors

Projection works well. You can make your own box projector or use a telescope or binoculars. However, don't look through the telescope's eyepiece or side-mounted finder scope while projecting the Sun's image onto a screen.

Eclipse Glasses

The American Astronomical Society has compiled a list of vendors where you can buy safe eclipse glasses. Make sure you carefully read the instructions that come with the glasses.
How to make the best use of solar eclipse glasses

NASA also recommends welder's glasses rated 14 or higher. These can be found at your local welding supply store. Keep in mind that welder glass grading may be different in different countries.

Solar Filters

You can use special solar filters to watch the Sun during a solar eclipse, but use the proper type of solar filter that is designed for eclipses. Check that filters do not crack under the Sun's magnified and focused intensity. Solar filters must be treated with care, or they can quickly become damaged and unsafe to use.
How to take pictures of a solar eclipse
Solar filters should never be used with optical devices such as telescopes and binoculars, unless it is a specialist solar filter designed for use with that particular device. If you are uncertain about whether a filter is safe, do not use it. Avoid all risks.

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Safely See a Solar Eclipse: Sunglasses Don't Work

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Always take precautions when watching a solar eclipse. Never look directly at the Sun without proper protective gear. DIY eclipse projector in a box.

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DIY Pinhole Projector to Safely Watch a Solar Eclipse

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One of the easiest and safe ways to watch a solar eclipse is with a DIY pinhole projector using 2 sheets of cardboard.

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60 Second Space: How to Make a Pinhole Projector to View the Solar Eclipse

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Space Stuff In 60 Seconds! How To Make A Pinhole Projector To View The Solar Eclipse You don't necessarily need fancy equipment to watch one of the sky's most awesome shows: a solar eclipse. With just a few simple supplies, you can make a pinhole camera that allows you to view the event safely and easily.

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ExploreLearning : Get hands-on, minds-on in math and science

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2D Eclipse Gizmo : Lesson Info : ExploreLearning

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Manipulate the position of the Moon to model solar and lunar eclipses. View Earth's shadow, the Moon's shadow, or both. Observe the Moon and Sun from Earth during a partial and total eclipse. The sizes of the three bodies and the Earth-Moon distance can be adjusted.

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2017 Solar Eclipse News and Articles

Aug. 21, 2017 marked a unique opportunity for scientists in the contiguous U.S. - for the first time in nearly a century, a total solar eclipse would sweep coast to coast, providing scientists under the path of totality with a rare chance to study the Sun and Earth in uncommon ways. Read the articles and news releases pertaining to this historic event.

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2017 Solar Eclipse News and Articles - NASA

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Aug. 21, 2017 marked a unique opportunity for scientists in the contiguous U.S. - for the first time in nearly a century, a total solar eclipse would sweep coast to coast, providing scientists under the path of totality with a rare chance to study the Sun and Earth in uncommon ways.

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Solar Eclipse 2017: Map, Guide and VR - CNN

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Ready for the 'Eclipse of the Century' on August 21, 2017? View the latest information on the solar eclipse, explore the interactive map and check out our live virtual reality coverage on the day of the event.

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5 NASA-approved ways to look directly at the total solar eclipse

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From the inexpensive to the wallet-breaking, there are lots of ways to watch this year's eclipse.

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ExploreLearning : Get hands-on, minds-on in math and science

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3D Eclipse Gizmo : Lesson Info : ExploreLearning

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Observe the motions of the Earth, Moon and Sun in three dimensions to investigate the causes and frequency of eclipses. Observe Earth's shadow crossing the Moon during a lunar eclipse, and the path of the Moon's shadow across Earth's surface during a solar eclipse.