On Aug. 21, millions of people in the continental United States will be looking up at the sky to witness a nearly once-in-a-lifetime event. The moon will cross between the sun and the earth, completely obscuring the sun. It will be the first solar eclipse seen in the U.S. since 1979.
During a total solar eclipse, viewers can see the corona, the outside of the sun’s atmosphere, flickering around the dark disk of the moon. During this event, both the sun and the moon appear to be about the same size because, while the sun is 400 times wider than the moon, it is also 400 times farther away from the earth, according to NASA. For an eclipse to occur, the moon has to be in the same spatial plane with the sun and earth, which only happens twice a month. The rarer part is that the moon also has to be new.
On Monday, all of these elements will fall into place in a 70-mile-wide band across the U.S. Pennsylvanians will not be on the path of totality, which last occurred locally in 1925.
While the eclipse will only be visible in full following a path between Oregon and South Carolina, Main Line area residents will be able to witness part of this rare celestial event. As long as it is a cloudless day, simply looking up to the sky—with proper eclipse-viewing eye protection—will offer views of a partial eclipse. Regionally, the best times to watch are from 1:21 p.m. to 4:01 p.m., and the eclipse will reach about 80 percent coverage at 2:44 p.m.
For safe viewing of the eclipse, gazers should use extreme caution. Staring at the sun with unprotected eyes can lead to irreparable damage. Sunglasses, cameras and counterfeit eclipse glasses will be insufficient for safe viewing. While most NASA-recommended suppliers of eclipse glasses are sold out, there are still alternatives.
Pinhole projection is a popular and low-tech option. You can observe the sun’s unusual shape by watching projected light through a hole in a card, or create a simple projector out of a cardboard box, as in this video from NASA. For an indirect viewing option touted by the American Astronomical Society, simply stand with your back to the sun and cross your fingers over one another to see the sun’s crescent shadows on the ground.
For extra cautious viewing, witness the phenomenon via live stream. Not only will it protect the eyes, but live streams will show the full eclipse. NASA, the Weather Channel and CNN will all offer streaming.
If you miss this celestial event, you only have to wait seven years to try again: the next total solar eclipse will be on April 8, 2024, and northwestern Pennsylvania is on its path of totality. In the meantime, get your pinhole projector ready.