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PlaygroundEquipment Blog
Wednesday, August 2, 2017

Solar Eclipses, and How to Watch Them


As some readers might know, there is a solar eclipse that is set to take place over North America on August 21, 2017. If you are reading this after that date, don’t worry—There will be more! In fact, eclipses generally happen at least twice a year, once in the spring and once in late summer. But this particular eclipse is special for a few reasons. It is the first total eclipse to occur over the mainland United States since June 8, 1918.

Solar eclipses occur when the moon moves in front of the sun, blocking all or part of it from view for observers on earth. A total eclipse, in which the moon completely blocks out the sun, is a rare occurrence that few people ever get to see. Most eclipses are either partial or annular.

Partial Solar Eclipses are the most commonly observed. These occur when the moon passes over part of the sun, blocking out some of its light. This makes the sun appear to be a crescent shape, much like the moon looks when the earth is blocking most of the sun’s light from it.

Annular Solar Eclipses are similar to total eclipses, in that the moon moves directly in front of the sun. However, the moon is not always the same distance away from the earth. This is why it appears to be larger on some nights than others. If the moon is directly in front of the sun, but too far away from the earth to block out its light completely, an annular eclipse is formed. When this happens, the moon blocks out the center of the sun, leaving only a bright ring of light visible around its edges.

Total Solar Eclipses are the hardest to see, because they require the moon to be directly in front of the sun, and also close enough to completely block it out. When this happens, certain areas of the earth will experience complete darkness for several minutes. To observers in these areas, it will appear as if the sun has completely disappeared (much to the terror of unknowing ancient civilizations).





 
When the moon passes in front of the sun, it cast a round shadow on the earth called an umbra (technically called an antumbra in the case of an annular eclipse). The umbra is about 60-100 miles wide and moves quickly, only covering any one particular point for about seven minutes. When this happens, it appears as though night has suddenly fallen in the middle of the daytime. This is the area directly between the earth, moon, and sun, where an observer must be standing to see a total or annular eclipse to its fullest extent.

Of course, those outside of the umbra will still see a partial eclipse. Even if the moon is only covering part of the sun it still blocks out some of its light, darkening a huge area on that side of the world. This area is called the penumbra.

Eclipse fans have been known to travel hundreds of miles for just a few minutes in the moon’s umbra. Sometimes the umbra’s path mostly crosses oceans, barely touching any land at all. But the eclipse coming up this August will have an umbra that almost perfectly cross the continental United States, beginning in Oregon and curving downward to cross South Carolina. The penumbra will cover most of North America, which means that a partial eclipse will be visible even in Alaska and Hawaii.




If you plan on watching an eclipse, it is important to use proper protection for your eyes. Looking directly at the sun, even when it is partly covered, can cause permanent retinal damage. The only time that it is safe to watch with the naked eye is while the sun is completely obscured for a few minutes during a total eclipse. However, there are still a few options for viewing partial or annular eclipses safely:

Solar Viewing Glasses are perhaps the easiest and safest way to watch a solar eclipse, and can be ordered online or found in some department stores. There are several high-quality designs with plastic frames, but these aren’t necessary. Simpler pairs with paper frames work just as well, and are very cheap. Regular sunglasses simply aren’t powerful enough to protect your eyes, even if you wear multiple pairs at once.

Indirect projection is a method which projects the sun onto a surface where it can be viewed safely. This is not quite the same as watching it happen, but does allow you to see the movement of the moon’s shadow.

Simple instructions for making your own pinhole camera can be found here: https://www.jpl.nasa.gov/edu/learn/project/how-to-make-a-pinhole-camera/

Cell phones or digital cameras can record images or footage of an eclipse which can then be viewed safely. However, long exposure photographs or video can harm camera lenses, especially large ones. There is also a good chance that cell phone pictures will be blurry or hard to see.

Eclipses are a rare and spectacular phenomenon which should be seen by everyone at least once.  Although they take some effort to find and watch safely, most people who have seen one would say that it was worth it. No matter where you live, it’s a good idea to look up when the next eclipse near you will be. While total eclipses like the one this August are particularly uncommon, there are plenty of opportunities to see partial eclipses or even lunar eclipses. Just remember to keep your eyes protected!


Sources:


https://www.vox.com/science-and-health/2017/7/25/15925410/total-solar-eclipse-2017-explained

 https://eclipses.gsfc.nasa.gov/solar.html

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