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Professors Demystify Eclipse for Merced Skygazers

August 17, 2017

As the frenzy surrounding the Aug. 21 solar eclipse begins to peak, physics Professor Wil van Breugel is using the opportunity to give Merced stargazers a crash course in the science and history of these astronomical curiosities.

“It’s important for people to fully appreciate the science,” van Breugel said. “This is an opportunity to try to explain things more fundamentally.”

An astrophysicist and lifelong educator, van Breugel recognizes that “astro-” inspires as much awe as “-physics” inspires anxiety. But van Breugel insists there’s no reason to fret. The fundamentals of solar eclipse science are surprisingly uncomplicated.

“A solar eclipse occurs when the moon is directly between the Earth and the sun,” van Breugel explained.

When light can’t pass through a solid object, the object casts a shadow opposite the light source. Take, for example, a beach umbrella. Sunlight shines on the umbrella but can’t penetrate the umbrella’s surface, so a shadow darkens the ground where light would otherwise have touched down.

The moon casts a similar shadow. And since the sun always shines, the moon’s shadow is always present. However, the Earth is not always in the shadow’s path. The darkening experienced during a solar eclipse is the Earth entering that shadow. But only a small fraction of the Earth’s surface experiences any perceptible dimming.

“Depending on where you are, the sun may be partially or entirely blocked by our moon,” van Breugel said. “For this eclipse, there will be a 60-mile-wide band that starts in Oregon and ends in South Carolina where you can see a full eclipse. But you can see a partial eclipse everywhere from San Diego to Canada, including Merced."