UW astronomy professor offers tips to observe April 8 solar eclipse

By Cheyenne Thomas As long as the skies are clear, residents will be able to watch a solar eclipse make its way across the sky over the United States on April 8. The eclipse will be visible as a partial eclipse in Wisconsin during the early afternoon hours on that day, and those who are interested in viewing the eclipse can do so using simple tools to view the event safely.

Dr. Jim Lattis, UW-Madison Astronomy Department professor and director of UW Space Place public education center, spoke about what a solar eclipse is and what Wisconsinites can expect to see on April 8. Generally, Lattis said, solar eclipses occur somewhere on the planet twice a year, but most of the time, eclipses occur over areas of the planet not inhabited by people.

“A solar eclipse occurs when the shadow of the moon falls on some part of earth’s surface,” he said. “If the alignment of the disks of sun and moon is close to perfect as seen from a given location, then we call it a ‘central’ eclipse. The moon’s orbit is elliptical, so sometimes closer or farther from earth. If close enough, the disk of the moon will completely cover the disk of the sun and we get a total eclipse. If the eclipse is central but the moon is near its greatest distance, then it will not completely cover the solar disk and we get an annular eclipse. If the alignment is not center-to-center, we see a partial eclipse.

Solar eclipses of some kind (central or partial) occur somewhere on earth on the average twice a year, but the paths often cross the polar regions and over the oceans, so they are rare at any given location. The path of a total eclipse is only about 100 miles wide, so even when the path crosses inhabited areas, most of the places in the region are outside of the path and experience only a partial eclipse. This is the case for Wisconsin on April 8.”

The last time Wisconsin experienced a partial solar eclipse was on Aug. 21, 2017. This time, the path of totality will again lie outside of Wisconsin, extending from Texas to New England and passing through southern Illinois. Because the path of totality will not pass over Wisconsin, Lattis said residents can expect to see somewhere between 80-90% of the sun covered by the moon, depending on where in the state you decide to watch.

“The closer to the path of totality you are, the more of the solar disk is covered by the moon,” Lattis said. “We quantify solar eclipses by using the fraction of the sun’s diameter that is covered by the moon at maximum. In Madison, at its deepest, the moon will cover about 89% of the sun's diameter. In Wausau, for example, the maximum will be more like 84%. The times of the beginning, middle, and end of the eclipse in Wausau will be 12:53 p.m., 2:07 p.m., and 3:19 p.m. CDT. During the roughly two hours from beginning to end, observers will see the sun’s disk partially cut off by the moon, leaving a crescent of solar disk. Observers in Wisconsin will be in direct sunlight during the entire eclipse.”

If a person wants to have a view of the total solar eclipse, Lattis said there are many locations along the path a person could visit.

“For a view of totality you would need to be somewhere along the path that runs from Mexico northeastwards through Texas, across the Ohio Valley, up into New England, and into eastern Canada,” he said. “There are many cities, large and small, along the path, such as San Antonio, Indianapolis and Buffalo. The chances of getting a clear sky on that day are greater in the far southwest.”

Since Wisconsin is not in the path of totality, Lattis said viewers have to take measures to protect their eyes when trying to view the eclipse. Eclipse glasses and pinhole projectors are both methods that can be used to view an eclipse when not in the path of totality which are safe for eyes.

“On the path of totality, when the disk of the sun is completely hidden, it is safe to view the totally eclipsed sun with the naked eye, but you must look away at the moment that the first bit of the solar disk reappears,” he said. “(Outside of the path of totality) eclipse glasses have filters dense enough to reduce the solar radiation to safe levels and to cut out the infrared and ultraviolet sunlight as well. A simple pinhole in a piece of cardboard or aluminum foil will project an image of the sun on any surface in the shadow opposite the sun. That image of the sun is safe to look at, and good enough to show the shape of the disk of the eclipsed sun.”

If eclipse glasses are not an option, there are two types of pinhole projectors that can be made and used to view a solar eclipse. The first is a simple card projector, made out of two pieces of card or paper. To make the projector, all that is required is two sheets of plain white paper or white cardboard and something sharp such as a thumbtack, pin or needle. Using the thumbtack or pin, a round, smooth hole is made in the center of one of the sheets of paper. Facing away from the sun, the piece of paper with the hole should be held above your shoulder, while the other is held in front of you. The image of the sun will be projected onto the paper through the pinhole, and the size of the sun can be made smaller or larger depending on how close together the sheets of paper are.

The second type of projector is a box projector. Similar to the simple pinhole projector, the box projector uses a long cardboard box to create an image of the eclipse. A small hole is made on one side with a piece of aluminum foil covering the hole. Using a pin, a round, smooth hole is made in the aluminum foil to allow an image of the eclipse to be projected on the inside of the box. To see this image, a sheet of white paper should be taped inside the box on the side opposite the hole. A head-shaped hole then should be cut into the bottom of the box so then a person would be able to look inside the box to view the image.

“Eclipses are very easy to observe safely,” said Mattis. “There is no need for eclipse glasses. You can even use a kitchen colander to project dozens of images of the eclipsed sun onto the ground.”

The total solar eclipse will also be live-streamed by organizations such as NASA that will have cameras in the path of totality. The next total solar eclipse will occur on Aug. 2, 2027, when it will cross North Africa, the Red Sea and the Indian Ocean. Wisconsinites will have to wait longer

Please see Eclipse, page 5

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