On Monday, April 8, the United States will experience a total solar eclipse — a rare astronomical event where the moon passes directly between the sun and the Earth, blocking out the sun’s light almost completely. The last total solar eclipse in the contiguous U.S. was in 2017, and the next one won’t be until 2044.
If the weather cooperates, people across the United States — from northeastern Maine to southwestern Texas — will be able to observe the eclipse using protective eyewear. Those in the path of totality, where the moon entirely covers the sun, will have the best view, but 99% of people in the continental U.S. will be able to see a partial eclipse. Weather permitting, those on the MIT campus and the surrounding area will see 93 percent of the sun covered, with the partial eclipse starting at 2:15 p.m. and reaching its peak around 3:29 p.m. Gatherings are planned at the Kresge Oval and the MIT Museum, and a live NASA stream will be shown in the Building 55 atrium.
Brian Mernoff, manager of the CommLab in the Department of Aeronautics and Astronautics, is an accomplished astrophotographer and science educator. Mernoff is headed to Vermont with his family to experience the totality from the best possible angle — but has offered a few thoughts on how to enjoy the eclipse safely, wherever you are.
Q: What should viewers expect to see and experience with this solar eclipse?
A: When you’re watching TV (the sun) and your toddler, dog, or other large mammal (the moon) blocks your view, you no doubt move over a bit to try to get a partial or full view of the TV. This is exactly how the path of totality works for an eclipse. If you are exactly in line with the moon and sun, it will be completely blocked, but if you start moving away from this path, your view of the sun will start to increase until the moon is not in the way at all.
The closer you are to the path of totality, the more of the sun will be blocked. At MIT, about 93 percent of the sun will be blocked. Those in the area will notice that things around you will get slightly darker, just like when it starts to become overcast. Even so, the sun will remain very bright in the sky and solar glasses will be required to view the entirety of the eclipse. It really goes to show how incredibly bright the sun is!
Within the narrow path of totality, the moon will continue to move across the sun, reaching 100 percent coverage. For this short period of time, you can remove your glasses and see a black disk where the sun should be. Around the disk will be wispy white lines. This is the corona, the outermost part of the sun, which is normally outshone by the sun’s photosphere (surface). Around the edges of the black disk of the moon, right as totality begins and ends, you can also see bright spots around the edges, known as Bailey’s Beads, caused by sunlight shining between mountains and craters on the moon.
But that’s not all! Although you will be tempted to stare up at the sun throughout totality, do not forget to observe the world around you. During totality, it feels like twilight. There is a 360-degree sunset, the temperature changes rapidly, winds change, animals start making different sounds, and shadows start getting weird (look into “shadow bands” if you have a chance).
As soon as totality ends, and you start to see Baily’s Beads again, put your solar glasses back on as it will get very bright again very fast as the moon moves out of the way.
Q: What are the best options for viewing the eclipse safely and to greatest effect?
A: No matter where you are during the eclipse, make sure you have solar glasses. These glasses should be ISO-approved for solar viewing. Do not use glasses with scratches, holes, or other damage.
If you are unable to obtain solar glasses in time, you can safely view the eclipse using a home-made projection method, such as a pinhole camera or even projecting the image of the sun through a colander.
The best view of the eclipse will be from within the path of totality, but even if you are not within it, you should still go outside to experience the partial eclipse. Use the NASA Eclipse Explorer to find the start, maximum, and end times, and then find a nice spot outside — preferably with some shade — put on your glasses, and enjoy the show.
For a closer view of the sun, find a friend that has a telescope with the correct ISO-certified solar filter. This will let you see the photosphere (or chromosphere if it is an H-alpha scope) in a lot more detail. If you do not have access to a telescope, NASA plans to livestream a telescope view throughout the eclipse. [The livestream will be displayed publicly on a large screen in Building 55 at MIT, rain or shine.]
The only time you can look at or image the sun without a filter is during 100 percent totality. As soon as this period is done, glasses and filters must be put back on.
After the eclipse, keep your glasses and filters. You can use them to look at the sun on any day (it took me an embarrassing amount of time to realize that I could use the glasses at any time instead of lugging out a telescope). On a really clear day, you can sometimes see sunspots!
Q: How does eclipse photography work?
A: This year I plan to photograph the eclipse in two ways. The first is using a hydrogen-alpha telescope. This telescope filters out all light except for one wavelength that is given off by hydrogen. Because it blocks out most of the light from the sun’s surface, it allows you to see the turbulent upper atmosphere of the sun, including solar prominences that follow magnetic field lines.
Because this telescope does not allow for imaging during totality as too much light is blocked, I also plan to set up a regular camera with a wide-angle lens to capture the total eclipse with the surrounding environment as context. During the 2017 eclipse, I only captured close-ups of the sun using a regular solar filter and missed the opportunity to capture what was going on around me.
Will it work? That depends on if we get clear skies, and how many pictures of my 1.5-year-old need to be taken (as well as how much chasing needs to be done).
If you would like to take pictures of the eclipse, make sure you protect your camera sensor. The sun can easily damage lenses, sensors, and other components. Here are some examples of solar damaged cameras. The solution is simple, though. If using a camera phone, you can take pictures through an extra pair of solar glasses, or even tape them to the phone. For cameras with larger lenses, you can buy cardboard filters that slide over the front of your camera or even buy ISO-approved solar film and make your own.
Q: Any fun, unique, cool, or interesting science facts about this eclipse to share?
A: If you want to get even more involved with the eclipse, there are many citizen science projects that plan to collect as much data as possible throughout the eclipse.
NASA is planning to run several experiments during the eclipse, and researchers with MIT Haystack Observatory will also be using four different technologies to monitor changes in the upper atmosphere, both locally and across the continent.
If you are interested in learning more about the eclipse, here are two of my favorite videos, one on “unexpected science from a 0.000001 megapixel home-made telescope” and one on solar eclipse preparation.
https://ift.tt/gvN95AS
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