This week’s question was asked by several Tomah residents
QUESTION: What about this solar eclipse in August?
ANSWER: This solar eclipse is a big deal, and you don’t want to miss it. How rare is a total solar eclipse? In any one location, a total solar eclipse occurs, on average, every 375 years. Even though folks know that a total solar eclipse is happening, the experience can be awe-inspiring, beautiful, even eerie and unsettling.
The last total solar eclipse to sweep across the entire continental United States was in 1918. The next total solar eclipse after Aug. 21 will be on April 8, 2024. It will start in Texas and go in a northeast direction, through Ohio and up into Canada.
The next total solar eclipse after that will be in 2045 and more southern than the 2017 eclipse. Aug. 21, weather permitting, is a don’t-miss opportunity. Astronomers are calling this one the “Great American Eclipse.”
The path of totality will stretch along a route from Oregon to South Carolina. The path of total shadow will be 60 miles wide. It will be billed as a partial solar eclipse for Monroe County. It will last two hours and 46 minutes, starting at 11:48 a.m. and ending at 2:34 p.m. Viewers will first notice that a little bit of the upper right-hand side of the sun is missing, as if someone took a bite out of the sun. The maximum will occur at about 1:12 p.m., meaning the maximum amount of sun covered by the moon. At maximum, a sliver of light will remain in the upper left corner of the sun. For viewers in Monroe County, about 87 percent of the sun will be covered by the moon.
The sky will darken, the temperature will drop a few degrees, birds will stop singing and start to roost, chickens stir and crickets will start to chirp. Animals think that night is coming on. The sky will take on an eerie grayish, dim glow. People have a sense that night is occurring in the middle of the day.
Total solar eclipses occur when we have a new moon. The moon comes between the sun and Earth and casts the darkest part of its shadow, the umbra, on Earth. The Earth moves into the shadow created by the moon.
If we get a new moon every month, why don’t we have a solar eclipse every month? Not only must there be a new moon, but the sun, moon and Earth must all be in a straight line. The orbit of the moon around the earth is not in the same plane as the orbit of the earth around the sun. The orbit of the moon is tilted five degrees from the orbit of the earth around the sun. That means that most months the moon’s position is either above or below the sun’s position when they are in the same part of the sky. In other words, they are not in a straight line.
During a total solar eclipse, the moon’s shadow is cast upon the earth. There are two parts to this shadow, an outer shadow that covers a wide region creating a particle eclipse, (penumbra) and a much smaller central shadow that creates the total eclipse (umbra). That central shadow creating that thin path is known as the path of totality.
Astronomers from all over the world will be studying this eclipse, so what will they look for? They will measure the temperature of the outer atmosphere (corona), a vast region of super-heated gas. Under normal conditions, the corona cannot be seen from the ground because it is overwhelmed by the brightness of the sun’s main disk, the photosphere. Scientists will study the sun’s magnetic field and determine how energy moves through the Sun and out into space. They will analyze the solar wind, which is particles moving out from the sun.
How can we safely view the eclipse? Only during totality is it safe to look directly at the eclipse with the naked eye. Before and after totality, eye protection is necessary for anyone in the narrow path of totality. For anyone at a place where a partial solar eclipse with occur, the use of solar filters is mandatory. Sunglasses are not sufficient.
During totality, when the moon completely covers the sun, the daytime sky will darken by a factor of 1 million. Normally, the brightness of the sun is so great that when 99 percent of the sun is covered by the moon, the leftover 1 percent is sufficient to make the sky remain blue.
We in the Tomah area will not be in totality, but we do want to get the most enjoyment from this eclipse. The sun’s rays, both visible and invisible, can cause massive damage to the sensitive tissues of the eye. This injury can occur without the viewer being immediately aware of it and it is permanent.
Normally, our common-sense reflexes protect us from looking at the sun for more than about a second. The sun is so bright that we squint, our eyes tear up, and we look away. During a partial solar eclipse, the sun is not nearly as bright, so the temptation is to stare at the sun for too long a time. But even a small piece of the sun is sending out dangerous ultraviolet light.
There are ways of enjoying one of nature’s greatest shows. First, a warning. Never look at the sun through a telescope or binoculars. Only use a telescope or binoculars if they are fitted with reliable solar filters designed to fit directly on the instruments and the operator knows how to use them.
Paper glasses with special filters made of protective material are being sold in countless outlets. Many organizations will be providing these cardboard-framed glasses free of charge. Amazon.com has ads for glasses at about a dollar each.
Another method is to make a simple pinhole projector. Cut a square out of the middle of a cardstock, tape a piece of aluminum foil over the hole, and put a pinhole in the foil. Catch the image of the eclipse on another piece of white cardstock held behind the pinhole. You can also make a nice pinhole projector inside a box, such as a large cereal box or shipping box.
Don’t miss this eclipse. Do hope for good weather and favorable viewing conditions on Aug. 21, so that you can observe this spectacular event!
Send questions and comments to firstname.lastname@example.org.
Larry Scheckel is a retired Tomah High School physics teacher.