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August 21, 2017: A small moon covers a gigantic sun

BY AMY SAYLE

The biggest astronomical event of the year (of the decade, really) for the United Sates happens August 21, 2017, when Earth’s Moon appears to pass in front of the Sun, causing a solar eclipse

If you are in the 70-mile-wide path of totality that cuts across the continent from Oregon to South Carolina, you can experience it turning dark in the daytime, planets and bright stars coming out, and memories that will last a lifetime. (Note to most readers in North Carolina: you will need to travel to get into the path of totality.)

You might wonder how can the Moon, which is relatively small, cover up the Sun, which is really, really big?

When you see the Moon in the sky, it might look pretty impressive. But it’s actually not that large compared with Earth. The Moon would fit across Earth nearly four times. This image shows their relative sizes (but not their relative distance):

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This photo shows the relative sizes of the Moon and Earth. The distance between them is not to scale.

Another way to think about the sizes of Earth and the Moon is to scale them both down. On a scale where 1 inch represents 25,000 miles, Earth would be the size of a chickpea, and the Moon would be roughly the size of quinoa.

How big do you think the Sun would be on this same scale?

Go ahead, take a guess: Earth as chickpea, Moon as quinoa, Sun would be how big across…?

(Really, take a guess before you keep reading.)

(Is someone near you right now? Ask them to guess, too.)

(Did you guess yet? Do it now! How big would the Sun be?)

(This is your last chance!)

Answer: On that scale, the Sun would be the size of a giant beach ball, 35 inches in diameter!

The Sun is gigantic: about 400 times bigger across than the Moon. But every once in a while, from our point of view on Earth, the Moon appears to cover the Sun—a solar eclipse.

http://moreheadplanetarium.org/sites/default/files/images/TSE%20Image.jpg

How can this be? It’s because the Sun is also about 400 times farther away than the Moon is. This makes the Sun and Moon appear roughly the same size in our sky.

On our 25,000 miles-to-1-inch scale, we’d have to carry the Sun beach ball more than a football field’s distance away to make the Sun and Moon appear the same size.

On Monday, August 21, 2017 around mid-day, rather than passing just over or under the Sun like it does most months, the New Moon will pass directly in front of the Sun. All of North America gets a partial solar eclipse. To witness the total solar eclipse, you must be within the narrow path shown on the map:  

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This map shows the path of totality across the United States. Click here for a zoomable version of the map.

Only in this path of totality can you get the full, dramatic, mind-blowing, life-changing experience. Totality lasts for up to two minutes and forty seconds depending on where you are in the path.

In North Carolina only a sliver of the western part of the state gets totality. For many in North Carolina, the closest places to travel for the total eclipse will be in South Carolina.

To learn more about the solar eclipse on August 21, 2017, check out the Morehead website: http://moreheadplanetarium.org/eclipse. If you aren’t convinced yet that it’s worth traveling to the path of totality, read this: http://moreheadplanetarium.org/2017eclipse (also see the links at the end to maps, weather prospects, and viewing tips.)

Important: To view the partial eclipse OR to view the partial phases of the total eclipse, you must have “eclipse glasses” or a special solar telescope. Only when the Sun is 100% totally eclipsed is it safe to look at directly.

We can’t do anything to make the 2017 eclipse happen sooner (except in the planetarium sky). But in the meantime, if you’d like to see the Moon through a telescope, please join us at one of Morehead’s November skywatching sessions (weather permitting):

  • Friday, Nov. 4, 2016 - Little River Regional Park
  • Saturday, Nov. 5, 2016 - Jordan Lake, Ebenezer Church Recreation Area

Image credits:

1) NASA

2) Morehead Planetarium and Science Center
3) Jay Pasachoff, Muzhou Lu, Craig Malamut, Hana Druckmüllerová
4) Eclipse Predictions by Fred Espenak, NASA's GSFC