On August 21, large swaths of America will fall under a total solar eclipse for the first time in almost 40 years. The phenomenon is much more dramatic than a partial solar eclipse, and PBS's series Space Time just released a wonderful new video to let you know what to expect.
While the moon is obviously much smaller than the sun, it is also much closer to Earth, making the two celestial bodies appear relatively the same size in the sky. This is a simple matter of fortunate coincidence. As the moon whirls around us and we whirl around the sun, every so often the three bodies line up just right so that the shadow of the moon falls on the Earth, completely blocking all sunlight in the center, or umbra, of the shadow.
A total solar eclipse is a rare chance to see the sun in a completely new light (or, without as much light to be more accurate). It's the only time you can directly observe the chromosphere with the naked eye—a layer of the sun's atmosphere with dramatic reddish tendrils of plasma that snake out into space. You will also be able to see the corona, the outer atmosphere that floats around the sun, usually hidden by the intense light of our host star. During totality, when the moon completely blocks the light of the sun, you can look at these phenomena with the naked eye—but and to put them back on before it ends.
While all of the United States will experience a partial solar eclipse, you need to get inside a 70-mile-wide band of shadow that will run across the continental U.S. to see the total solar eclipse. The shadow runs through Oregon, Idaho, Montana, Wyoming, Nebraska, Kansas, Iowa, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina before heading out to sea over the Atlantic. You can expect about two and a half minutes of daytime darkness if you travel to the path of totality, but if you miss it, you will have to wait until 2024 to see a total solar eclipse in the United States again.