The upcoming total solar eclipse on Monday August 21 is exciting, but not because total solar eclipses are scientifically rare. In fact, an average of once every 18 months, a total solar eclipse is visible from some place on the Earth’s surface. What makes this rare for humans is that these usually occur over water or in sparsely populated areas. Consider this – the last time a total solar eclipse impacted the lower 48 states was in 1979 and another one will not have such visibility across the U.S. until 2045. This one is very special because it’s the first time in American history one will be visible across a 70-mile wide swath from coast to coast. NASA estimates 500 million people will be able to see this eclipse, either partially or in totality: 391 million in the U.S., 35 million in Canada, and 119 million in Mexico.
What is a Total Solar Eclipse?
A total solar eclipse occurs during the phase called a New Moon; the moon passes directly between the sun and Earth, but this only happens when the moon is at its closest position to the Earth. Although the moon orbits the Earth about once every month, it’s orbit is tilted at about 5 degrees from the Sun-Earth orbital plane and elliptical, so the moon rarely casts a shadow on the Earth’s surface. Normally, the bright yellow surface of the sun (photosphere) is all we see. When the moon blocks out this intense light, this enables observation of the much dimmer solar atmosphere (corona), which appears as a pearly-white halo. This is a beautiful sight to see, but be careful as explained later.
A solar eclipse as it travels across Earth’s surface can last as long as 3 hours in partiality, however, the longest period the moon will completely block the sun at any given location will be about 2 minutes, 40 seconds. Against one’s intuition whereas the sun and moon rise in the east and set in the west, the shadow cast by a solar eclipse moves from west to east. The first landfall of the eclipse in the USA will be Lincoln Beach, Oregon starting at 9:05 a.m. PST, with totality starting at 10:15 a.m. During the next hour and a half, the path of totality will cross through Oregon, Idaho, Wyoming, Montana, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, and North and South Carolina. The total eclipse across the USA will end near Charleston, South Carolina at 2:45 p.m. EST.
Protecting Your Sight
Perhaps you remember your parents or teachers warning you to never look directly at the sun. Some people are under the misconception because most of the sun is blocked during a total eclipse, it is safe to look at it. That is absolutely false except for the few moments of totality. Looking at the Sun without protective solar eyeglasses can cause permanent damage to your sight. Because of the overall darkness, the pupils dilate which allows a great deal of powerful sunlight light to enter ones eyes. It only takes 30 to 60 seconds staring at an eclipse to cause retinal damage, called solar retinopathy. The retina absorbs the intense light from the Solar Corona thereby damaging cells. It is painless, so people may not realize they incurred damage until later on. Symptoms include loss of visual acuity (sharpness of vision), blind spots, changes in color vision, or distortion when looking at straight lines or grids.
Eclipse Sight-Saving Tips
- Don’t wear ordinary sunglasses because even dark ones are not strong enough to protect your eyes.
- Be aware of fakes – Amazon recently discovered unscrupulous dealers were selling unsafe solar eclipse glasses and they’re issuing refunds.
- Only wear welding glasses if they are #14, which is much darker than an arc welder typically wears.
- Don’t use solar filters that are scratched or damaged.
- Don’t wear solar eyeglasses and look through a camera, telescope, or binoculars because this magnifies the rays and negates the glasses’ protection. However, you can use these instruments if they are equipped with special solar filters.
- Do build your own pinhole box in a matter of minutes, which some eye experts say is safer than using solar eclipse glasses (and it’s a great kid-friendly activity!).
- Do use specially designed solar eclipse glasses and viewers to block the sun’s harmful rays. To date, only four manufacturers sell eclipse glasses and handheld solar viewers that meet international safety standards:
Of course, Mother Nature can ruin even the best laid plans. If it is completely overcast, the eclipse won’t be visible, but it will be eerily dark outside. So, by all means, if you are one of the 500 million people who is able to see this on August 21, go ahead and enjoy this rare event. Just be careful – and don’t look at the eclipse unless you follow the aforementioned precautions.