5 things to know about the total solar eclipse on Aug. 21

Near the end of August, everyone in North America will see at least some part of a solar eclipse- the first total solar eclipse visible in the United States in 38 years!  Here are five things you need to know about the upcoming solar eclipse and what you can expect to see where you are.

Lunar eclipse vs. solar eclipse: What's the difference?
These are the two types of eclipses that are so often talked about, but just as often confused. It's time to set the record straight. Both eclipses have to do with the position of the sun, earth, and moon, as well as shadows.

A lunar eclipse is the more common of the two, often occurring a few times a year. This occurs when the earth passes directly between the sun and the moon so that the earth casts a shadow onto the moon’s surface. Some sunlight still does reach the moon, however much of it passes through earth’s atmosphere first, which has the effect of filtering out much of the blue light from the sun. This causes the moon to appear red to those viewing from earth. It is this color that gives total lunar eclipses their ominous nickname, "the blood moon."

Image courtesy of NASA

The solar eclipse is the rarer of the two, even though they also occur consistently every 18 months. The key difference is that a solar eclipse happens in the new moon phase, when the moon passes directly in between the sun and the earth. However, since the moon is much smaller than the earth, the shadow it casts on the earth is much smaller, making solar eclipses more difficult to see then their lunar cousins.

Image courtesy of NASA

Those lucky enough to see the August 21 solar eclipse are in for a spectacular sun, as day briefly turns to night for a few minutes in the middle of the afternoon.

It's a rare U.S. mainland visit
As mentioned above, what makes seeing a total solar eclipse so rare is just how small the shadow of the moon is. For the upcoming eclipse, the area where you will be able to see the sun completely covered by the moon-- known as the “path of totality”-- is only about 70 miles wide. While areas away from this zone will still see the sun partially blocked, only areas within this narrow zone will experience the eclipse in its full brilliance.

Map courtesy of NASA

Many things effect where this narrow zone of totality sets up on the earth, including time of year, rotation, and tilt of the earth. Because of all of these factors, a United States mainland crossing is actually very rare. The last one to occur in the lower 48 states was actually in 1979, but it was mostly confined to the far northwest (Washington and Montana). The last total solar eclipse that was witnessed by a considerable number of people in the United States occurred nearly half a century ago on March 7, 1970.

The good news is we won't have to wait another half century to see another one! Another solar eclipse will traverse the United States in April 2024. 

Map courtesy of NASA

The sun's super-heated atmosphere
For those lucky enough to be in the path of totality, they’ll be treated to the beauty of the corona. But keep your limes in the fridge: I’m not referring to the popular alcoholic beverage. Instead, I'm talking about the incredible atmosphere of the sun. On the average day, the sun is far too bright to see the corona. In fact, the only time you are able to see it with the naked eye is during a total solar eclipse.

Image courtesy of NASA

The corona has been fascinating astronomers for centuries because it is still largely a mystery to us. Temperatures on the surface of the sun have been measured to be about 10,000°, but the corona that surrounds the sun averages temperatures of over 1,000,000°. Yes, you read that right, over 1 million degrees Fahrenheit-- but scientists are still clueless as to why this is. Regardless, it makes for an incredible sight to see for the lucky few who witness it during its brief 2-4 minute appearance. 

Image courtesy of NASA

An eerie twilight
Unlike their lunar cousins which occur at night, solar eclipses occur during daylight hours. The moon moving in front of the afternoon sun will cause the effect of briefly turning day into night for those closest to totality. Most others will experience a type of temporary twilight, but at the same time a very different type of twilight from those in the evening.

Colors in the sky will look a little strange due to the differences in light reaching our planet. Expect the deepest, darkest coloring closest to the sun, while the horizon glows in every direction. If you are outside the city, animals like birds and crickets tend to go quiet as the eclipse peaks. Temperatures have also been known to drop between 5-20°F as we briefly lose the sun's full heating effect during what is typically the hottest period of the day.

The eclipse where you live
The question on everyone’s minds is of course, “What will it look like where I live?” Well, the good folks at Google teamed up with the University of California, Berkeley to answer this question for you with the Eclipse Megamovie. Simply enter your city at the top of this page, and you can run through exactly what the eclipse will look like at your home, and the times to watch.

Image: Eclipse MegaMovie 2017

In Washington, D.C., for example, the eclipse will peak just after 2:42 pm on Monday, August 21, with about 81 percent of the sun covered. Since the sun is not fully covered in this area, YOU MUST WEAR EYE PROTECTION when viewing the eclipse or you could do severe damage to your eye. It is only safe to view the eclipse with the naked eye if the sun will be fully covered.

To download a map showing the path of the eclipse, click here

What will D.C. see?
If you want to see more coverage, you'll need to head to the “zone of totality,” Cities like Columbia, S.C. and Nashville, Tenn. are two of the more major cities that will witness full coverage for a brief period of time (about a 6 to 8 hour drive from D.C.).

Hoping to catch a complete solar eclipse in D.C.? Well, I'm sorry to say, you will be waiting quite a while. The city itself has never seen a total solar eclipse since its approval all the way back in 1790. In fact, the last time the zone of totality passed over the region where Washington, D.C. now stands was back in 1478. This came just 27 years after a total solar eclipse in 1451, so the 1400 would have been a great year for the city.

So when is the next one? Just over four centuries away on September 12, 2444. That is the only total eclipse for Washington, DC. this millennium. Oh, and it will only last a little over 30 seconds. Needless to say, the District is not the city to be this millennium if you’re an eclipse lover. Where's the best place to be? How about the city of Cabondale, Ill., just south of St. Louis, Mo., which will not only experience the full glory of the eclipse in August, but also a total solar eclipse in 2024 as well. 

Click here to see NASA's interactive map showing the path of totality