Are you one of the lucky ones who has seen a total solar eclipse in person? Whether you are a solar eclipse veteran or have yet to see your first one, the Great American Eclipse is coming Monday, August 21, 2017! All of North America will be able to see the Moon cover at least part of the Sun for 2-3 hours. But, the best part of the show will occur for only a couple minutes, reserved for viewers in the narrow path between Oregon and South Carolina, when the Moon will completely cover the Sun’s face! The skies will darken to twilight levels with sunset colors on the horizon, and Sun’s magnificent corona will be visible. For many Americans, this will be a once in a lifetime opportunity to see a total solar eclipse from just a day’s drive away. If you live here in Bloomington, Indiana, you’ll have to drive to either Kentucky or Illinois to be within the path of totality (the links here show the major cities in each state that are in this path).
To be able to view a total solar eclipse, when the Sun is fully blocked out, you have to be at the location within the darkest part of the moon’s shadow, the “umbra.” The map below shows the path of the total solar eclipse, which is only roughly 70 miles wide, and also shows at what local times totality will occur. The moon’s shadow will hit the United States on the West Coast in Oregon at about 10:15 am Pacific Time, and make its way across the United States, passing over Carbondale, Illinois at 1:21 pm Central Time, and then Hopkinsville, Kentucky at 1:25 pm Central Time, reaching South Carolina at 2:45 pm Eastern Time. At each location the total solar eclipse will last for just a little more than two minutes, so don’t be late!
Total solar eclipses require a few conditions to occur. Though the Moon is actually hundreds of times smaller than the Sun, by a cosmic coincidence, they are both at the right distances to appear to have the same size in the sky. The plane of Moon’s orbit around the Earth is slightly tilted relative to the plane of the Earth’s orbit around the Sun, therefore we have to wait for two periods during the year when the three bodies are nearly aligned in a straight line to expect an eclipse. These periods are called “eclipse seasons” and last typically 34 days. During these seasons, solar eclipses have a chance to occur during the new moon phase, when the side of the Moon facing us is completely dark.
This makes total solar eclipses a very rare event at any one location. The last time a total solar eclipse occurred in the United States was in 1991 in Hawaii, but many were disappointed by cloudy weather. Prior to that, in 1979 the total solar eclipse only crossed through the northwestern contiguous United States. The last time a total solar eclipse crossed from the western to eastern United States was in 1918!
One last thing I’ll talk about is that it’s extremely important to view the solar eclipse safely. Staring at the Sun without protection for your eyes is dangerous even when the Sun is partially covered. To look at the Sun properly, you’ll need to look through a specialized solar filter. Sunglasses or handmade filters won’t suffice, as light from all parts of the electromagnetic spectrum can still damage your eyes. You can buy simple solar eclipse glasses (shown in accompanying image), and they should adhere to the ISO 12312-2 standard, which means that they reduce visible sunlight to safe levels and also block out solar ultraviolet and infrared radiation. Major viewing sites may sell these glasses, but consider obtaining them beforehand (some well-known brands are listed below). It is also safe to project an image of the Sun onto a screen using a telescope, binoculars, or even a pinhole in a piece of paper. It is safe, however, to look at the Sun unprotected when it is completely covered, signaled by the sudden darkness of the sky, as the Sun will be no brighter than the full Moon.
I hope you’ll make plans to see the total solar eclipse this year (or maybe you already have). Plan ahead as many places will likely be crowded and have a backup plan in the unfortunate case of cloudy weather. If you happen to miss out this year, a total solar eclipse will be visible from here in Bloomington in 2024!
For Everyone on the IU Campus
The first day of classes is the same day as the eclipse! If you cannot make it to a viewing site within the path of totality, College of Arts & Sciences and the Council for Arts & Humanities are hosting Celest Fest, where they will be hosting viewing parties and other activities. Solar eclipse glasses will be provided, so don’t miss this opportunity to see the partial eclipse safely!
Links and Other Info
Here are a few companies/organizations that manufacture eclipse glasses: