Guide to the August 21 Solar Eclipse

What is “the Eclipse” that everyone’s talking about?

Day will become night on Monday, August 21, 2017 as parts of North America experience a total solar eclipse. A solar eclipse occurs when the moon moves between the earth and sun and blocks light from the sun, casting a shadow on the earth. Total solar eclipses occur about every 18 months somewhere on Earth, when the earth, moon, and sun line up perfectly. But this is the first one in 99 years to cross the United States from the Pacific to the Atlantic, and the first total solar eclipse to occur in the continental United States since 1979.

solar eclipse

Image by NASA

You will probably hear scientists talking about the “path of totality,” which refers to a 70-mile-wide stretch across the United States, from Oregon to South Carolina, where the moon will completely block the sun for several minutes. The moon will cast a central shadow that, in the middle of the afternoon, will make the sky dark enough to see stars. Only the “corona,” or pearly-white outer atmosphere of the sun, will be visible along this path.

If you are watching from outside the path of totality, you will probably still see something! The day may turn from being very bright to seeming cloudy or dark. In Philadelphia, at 2:44 p.m., approximately 79.9% of the sun will be obscured by the moon.

solar eclipse

Image by NASA

How Do I Watch?

NASA Television will air a four-hour show, Eclipse Across America, that will include live video plus coverage of eclipse-related activities throughout the nation. At 12 Eastern Daylight Time on August 21, visit to be directed to the broadcast. More than 50 high-altitude balloons, 11 spacecraft, at least three NASA aircraft, and astronauts aboard the International Space Station will capture images before, during, and after the eclipse. The Academy will be streaming the NASA coverage in our auditorium on Monday, and we welcome all visitors to enjoy it with us throughout the afternoon from 12:30 to 4 p.m.

Viewing the Eclipse Safely

If you choose to go outside to view the eclipse, you must be very careful! The sun is so bright that staring at it can damage cells in your retinas, even if only a part of it is visible. You need to protect your eyes using eclipse viewing glasses or hand-held solar viewers that meet the ISO 12312-2 international safety standard for such products. You also will need professional-grade solar filters to cover binoculars, telescopes, or cameras.

solar eclipse

Image by NASA

On Monday from 1 to 3 p.m. in Dinosaur Hall, we will be making pinhole eclipse viewers and sharing information about eclipses and safe viewing. Pinhole viewers are used to create an inverted image of the sun with your back to the sun. You can make an eclipse viewer on your own at home! See below for instructions.

Make Your Own Eclipse Viewer

Punch a small, clean pinhole in one piece of cardboard. Face your back to the sun and let the sunlight fall through that hole onto a second piece of cardboard, which serves as a screen, held below it. An inverted image of the sun is formed.

To make the image larger, move the screen farther from the pinhole.

To make the image brighter, move the screen closer to the pinhole.

Do not make the pinhole wide or you will only have a shaft of sunlight rather than an image of the crescent sun. Remember, this instrument is used with your back to the sun. The sunlight passes over your shoulder, through the pinhole, and forms an image on the cardboard screen beneath it.

Do not look through the pinhole at the sun!