At new Moon on August 21, the path of a total solar eclipse will cross the entire continental US. The Moon will pass directly between the Earth and the Sun, and the shadow of the Moon will fall upon the Earth. Observers at the center of the shadow, in a band about 60 miles wide, going from roughly Salem, OR, to Charleston, SC, will see the Sun completely covered by the Moon for up to about two and a half minutes.
For everybody else in the continental US, including people near Philadelphia, the Sun will never be completely covered by the Moon. Instead, the Moon will appear to take a “bite” out of the Sun. The closer you are to the line of total eclipse, the bigger the bite will be. In Philadelphia, about 75% of the Sun will be covered by the Moon. As seen from here, the eclipse starts at about 1:21 pm, reaches its peak at 2:44 pm, and ends at 4:01 pm.
Even though most of the Sun is covered, there will never be a time in Philadelphia where it is safe to look at the Sun directly. It only takes seconds of staring at the Sun for permanent eye damage to occur. There are no commonly available household items through which it is safe to look at the Sun.
However, nature has provided us with a handy way to see the crescent Sun: look in the shadows of trees! The normally round images of the Sun cast on the ground by light peeking between the leaves will look crescent-shaped, as shown in picture to the left.
This is a fun, completely safe way to view the eclipse. Be sure to look only at the ground, not back at the Sun through the trees! Of course, the news will be wall-to-wall eclipse coverage, so you can get great views from the center of the path on your TV or online. For more information, please see https://eclipse2017.nasa.gov
Jeff Goldader will be starting his fourteenth year as an Upper School Science Teacher at Baldwin, teaching Honors Physics in 9th grade, and AT Physics and Astronomy in 11th and 12th grade, in September. He holds a BSc in Physics and Astronomy from the University of Washington in Seattle, and a PhD in Astronomy from the University of Hawaii at Manoa. Before coming to Baldwin, he had a research fellowship with the Hubble Space Telescope project, and taught astronomy at the University of Pennsylvania for five years. This will be his third total solar eclipse, which he will be spending desperately dodging the clouds in South Carolina.