AUG 11, 2017 8:30 AMBY LOIS YOKSOULIAN | PHYSICAL SCIENCES EDITOR
Leslie Looney is a University of Illinois astronomy professor and director of the Laboratory for Astronomical Imaging. He spoke with News Bureau physical sciences editor Lois Yoksoulian about what to expect for the Aug. 21 total solar eclipse.
What is a total solar eclipse? Are they rare?
A total solar eclipse is when the moon completely blocks out the sun – it will be dark during the day. A total solar eclipse occurs when the moon is perfectly aligned between the sun and Earth. Since the moon’s orbit is inclined by 5 degrees and a total solar eclipse can only occur when the orbits are completely aligned, total solar eclipses only happen somewhere on Earth every 18 months or so. Every 18 months is not really rare, but since only those lucky few in totality can see them, a total solar eclipse can seem rare. For example, there has not been a total solar eclipse in Illinois since 1869, two years after the founding of the University of Illinois.
Why is the Aug. 21 eclipse taking the path that it is and why is southern Illinois such a popular viewing destination?
The eclipse path is determined by the relative positions of the moon, Earth and sun, which depends on their orbits. For every eclipse path, one location will have the longest eclipse duration, which is the best place in the world to see that eclipse, discounting weather. On Aug. 21, the shadow in southern Illinois will be 71 miles in diameter and moving at nearly twice the speed of sound. So, the location of the longest duration is in southern Illinois with two minutes and 41.6 seconds. The University of Illinois viewing event will be in the closest village to the longest duration with easy I-57 access – Goreville, Ill., with two minutes and 39.8 seconds. However, anywhere in totality is a good place to see the total solar eclipse.
What will the eclipse look like along the path of totality?
The moon completely covers the sun and you are standing in the shadow of the moon. This creates an eerie and weird darkness, revealing stars and planets in the daytime and the ghostly solar corona. These, along with a small temperature drop and the confused quiet of birds and animals combine to provide the most exciting few minutes in astronomy.
What time will the eclipse happen?
In Illinois, the eclipse will take about three hours in total as the moon moves across the face of the sun. The moon makes first contact with the sun around 11:53 a.m. Over the next hour, the moon slowly blocks more and more of the sun. In southern Illinois, the moon blocks the sun completely and totality starts at 1:20 p.m., lasting up to two minutes and 41 seconds. Afterward, the moon slowly moves off the sun with the eclipse ending at 2:48 p.m. In Urbana-Champaign, totality will not occur, but the sun will be mostly blocked, which will happen around 1:21 p.m., too.
Urbana-Champaign is not along the path of totality, so what will it look like here?
The sun will be 93 percent blocked, which, surprisingly, you won’t really notice. However, if you look at the sun with eclipse glasses, it will look very cool. I encourage you to look in the shade of trees or bushes. You don’t normally notice, but the shade has tens to hundreds of little images of the sun projected by small holes in the leaves or canopy. During a partial eclipse, these will look more and more crescent-shaped as the eclipse proceeds, which is really surprising. This is one of my favorite effects during a partial eclipse.
Last but not least, what is the best and safest way to observer the eclipse?
Staring at the sun is bad for your eyes, and you can permanently damage them. Do not stare at the sun – no matter if it is eclipsing or not. Do not use sunglasses to look at the sun – that is even worse than using your naked eyes. You must use eclipse glasses, which block 100 percent of harmful UV light and 99.999 percent of intense visible light. You can also make a simple pinhole camera out of a cereal box to project the image of the sun during the eclipse. During totality you will not need any eye protection – take in the beauty of the event. But once any sunlight pokes through, the eclipse glasses have to go back on.