By Richard Schmidt, U.S. Naval Observatory (ret.)
It is a remarkable coincidence that the Sun is both 400 times more distant than the Moon from the Earth and also about 400 times its diameter. This enables the disk of the Moon to completely blot out the brilliant light of the solar photosphere while leaving uncovered its brilliant extended atmosphere, the solar corona, during the rare event we call a total solar eclipse.
This totality can only be witnessed from within the 70-mile-wide path that the shadow of the Moon will trace along a hemisphere of the Earth. And on August 21 this year that eclipse path will (for the first time in recorded history) cross exclusively the continental United States, from northwest to southeast. Millions of eclipse watchers are expected to converge upon this exclusive viewing path, in hopes of glimpsing a few minutes of an unrivaled astronomical spectacle—weather permitting.
If you will be staying in Burleith for the eclipse you need not completely miss out; the partial phase of the August 21 eclipse could be the first visible here since March 1970. Washington skies were cloudy for the last five partial eclipses of 2000, 1994, 1984, 1979, and 1974. As partial eclipses go, this will be a good one—the Sun will be high above the horizon for the entire nearly three-hour duration, and 81% of the Sun’s disk will be covered at maximum eclipse. Should we be clouded out again, our next partial eclipse as good as this one will occur in April 2024.
One can safely follow the progress of the eclipse as the Moon travels from West to East in front of the Sun by using aluminized mylar and paper “eclipse glasses” which reflect most of the light of the Sun from UV to IR. It happens that the Glover Park Ace Hardware has a supply selling for $2 each. The image will be as small as an aspirin held at arm’s length, but still large enough for you to marvel at this celestial sky show.