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Solar eclipse: The science behind the spectacle

The phenomenon requires the Moon being almost exactly at perigee.

A total solar eclipse occurs when the Moon completely covers the Sun's disk. Image by Luc Viatour, CC BY-SA 3.0.
A total solar eclipse occurs when the Moon completely covers the Sun's disk. Image by Luc Viatour, CC BY-SA 3.0.

The prospect of a solar eclipse can be intriguing, and on Monday, April 8, much of the U.S. and Canada had the unusual opportunity to witness a partial or total eclipse (dubbed the Great North American Eclipse by some media outlets).

The solar eclipse will first be visible in a narrow strip on the Pacific Ocean and later in North America, starting at the Pacific coast before ascending northeasterly through Mexico, the U.S., and Canada, before culminating in the Atlantic Ocean.

With the eclipse, the dark silhouette of the Moon, our only natural satellite, will completely obscure the intensely bright light of the Sun, allowing the much fainter solar corona to be visible.

Nahum Arav, a professor of physics in the College of Science at Virginia Tech, has informed Digital Journal about the science behind the solar eclipse.

In terms of what exactly a solar eclipse is, Professor Arav explains: “A solar eclipse occurs when the moon covers part of the sun, known as a partial eclipse, or when the moon covers the entire disk of the sun, known as a total eclipse.”

With more specific detail, Arav adds: “When the moon’s orbit puts it directly between the Earth and the sun, the moon casts a shadow on the surface of the Earth. The central part of that shadow, the umbra, is fully shaded, while the outer region, the penumbra, is only partially shaded. Communities that happen to be in the path of the umbra — that is, the path of totality — will see a full eclipse, while those in the penumbra will see a partial eclipse.”

In terms of why solar eclipses do not happen very frequently, Arav explains: “Solar eclipses happen about twice a year, so they are not that rare. However, most of them are not observed from the United States and most of them are not total. We’ll have to wait until 2045 for the next solar eclipse that crosses a significant portion of the continental U.S.”.

The phenomenon requires the Moon being almost exactly at perigee (making its angular diameter as large as possible).

In terms of the best location for the eclipse, this was Southwest Virginia. Here Arav sets out why this was the case: “Viewed from our region, this will be the most the sun will be covered by the moon — 88 percent — until 2078.”

This means: “The 88 percent drop in the solar light will be visibly noticeable. Because we are quite close to the path of totality, the sun will resemble a crescent moon during the eclipse. It’s also very important that you only view the eclipse through safe viewing devices.”

Please note: Looking directly at the Sun can lead to permanent eye damage, so special eye protection or indirect viewing techniques are used when viewing a solar eclipse.

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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