Jay Pasachoff is Field Memorial Professor of Astronomy at Williams College, Williamstown, Massachusetts, and Chair of the International Astronomical Union Working Group on Solar Eclipses. Today marks his 66th solar eclipse.
Total Solar Eclipse
For the first time in 99 years, the narrow band of the Moon’s shadow will cross the United States from coast to coast, making a total solar eclipse for those in that narrow path. Everyone else in the United States will be able to see a partial solar eclipse, though the difference between totality and a partial eclipse is so dramatic that those outside the path of totality might not even notice that anything was going on.
Within totality, for those in a 70-mile-wide path from Oregon to South Carolina, the Sun will be safe to look at directly, since the everyday solar disk will be hidden by the Moon and only the glorious corona–the halo around the everyday Sun that is normally hidden by the blue sky–will become visible. As the Moon entirely covers the everyday Sun, bright sunlight that shines through the deepest valley on the edge of the Moon is so bright in contrast that it is called the “diamond-ring effect.”
Before or after totality for those in that path, or for everyone off to the sides, part of the everyday Sun remains visible. It is not then safe to look directly at the Sun–as it isn’t on an ordinary sunny day. Any part of the everyday Sun is too bright to stare at safely. Inexpensive solar filters have become available. And when the Sun is more than half covered, you can see the shape of the remainder by making a “pinhole camera,” projecting the solar image while facing away from the Sun. But anyone merely in the zone of the partial eclipse won’t see any of the dramatic effects that occur in the zone of totality.
In totality, people will cheer in awe at the phenomena, and scientists will make measurements that will help explain the outer layers of not only our Sun but also of billions and trillions of stars like the Sun. Students may be inspired. The Sun will be become least 60% covered from everywhere in the U.S.