The air will cool, the wind will die down, and birds will grow silent. Bright stars and planets will wink to life in the midday sky, and a dusky glow will encircle the horizon at 360 degrees.
For individuals in the path of totality for the solar eclipse over Indiana on April 8, 2024, nature will put on a show both magical and eerie for approximately four minutes. And it won’t happen again anywhere in the state until 2099.
“There’s nothing that combines the sense of predictability and rarity quite like a solar eclipse,” said Patrick Motl, director of the IU Kokomo Observatory and professor of physics at IU Kokomo, one of five IU campuses that will experience the eclipse. “There really aren’t any other natural phenomenon that can be predicted down to a fraction of a second hundreds of years in advance.”
A total eclipse occurs when the moon passes directly between the sun and the Earth, placing the Earth in its shadow. In 2024, five IU campuses will fall in the direct path of this phenomenon — known as the path of totality — with IU Bloomington landing closest to the path’s center line.
In Bloomington, the eclipse will last four minutes and three seconds, starting at approximately 3:05 p.m. At three other IU campuses — IUPUI, IUPUC and IU East — the eclipse will last slightly under four minutes, starting at approximately 3:06 p.m. in Indianapolis and Columbus and 3:08 p.m. in Richmond. At IU Kokomo, which falls near the northernmost edge of the path of totality, the total eclipse will last less than a minute, starting slightly after 3:08 p.m.
The path of totality
The time of the eclipse and the duration of totality are based upon the relative distances between the sun, moon and Earth, as well as factors such as the moon’s phase and axial tilt of the Earth and moon, said Catherine Pilachowski, IU Distinguished Professor and Daniel Kirkwood Chair of Astronomy in the College of Arts and Sciences at IU Bloomington. All of these conditions are perfectly predictable due to the gravitationally bound behavior of the solar system.
The path of totality refers to the latitudinal area that experiences a full eclipse, said Edward Rhoads, a lecturer in physics at the School of Science at IUPUI. The closer to the edge of this range, which is based upon the distance between the poles of the moon, the shorter the duration of the eclipse. Any locations outside the path of totality will only experience a partial eclipse.
According to Rhoads, the path of totality is not only rare because it occurs so infrequently, but also because its range is so narrow. Although the Earth experiences a solar eclipse every six months, on average, it’s only visible across a small strip of the planet’s surface. On April 8, 2024, the area that will experience a total solar eclipse is only 100 miles wide.
The experience of totality
The period of time when the sun is completely shadowed by the moon is the totality of the eclipse, Motl added. During this time, observers are in the “umbral shadow” of the moon. If the moon is only partly obscuring the sun — as is the case before and after a full eclipse, or in the areas outside the path of totality — this partial shadow is the “penumbral shadow” of the eclipse.
The brief period of the total eclipse is the only time during the event when it’s safe to look toward the sun without protective lenses.
“Totality itself is very awe-inspiring,” said Phyllis Lugger, a professor of astronomy at IU Bloomington who witnessed the total eclipse of the sun on Aug. 21, 2017, in Salem, Oregon. “It’s a remarkable shared experience that causes people with different backgrounds on different parts of the globe to be similarly awe struck by the wonders of the natural world.”
Fritz Kleinhans, an emeritus associate professor in the School of Science at IUPUI who has seen five total solar eclipses, said an eclipse can often seem to pass by “in the blink of an eye” because there’s so much to experience.
“Advance preparation can really pay off,” he said. “I recommend creating a mental check list of all of the phenomena you want to see so you don’t forget them in all of the excitement.”
What else to expect
The other unusual natural phenomenon that accompany the eclipse are attributable to the moon’s shadow, Motl said. The lack of sunlight will cause a noticeable drop in temperature — about 10 degrees — and the darkness will cause birds to roost. The wind will stop because the absence of the sun’s rays will lower the temperature differential between the air and ground. The circular glow at the horizon is due to sunlight remaining visible beyond the range of the path of totality, despite the darkness at the sky’s zenith.
“A total eclipse is the only time that the ‘ghostly’ light of the corona can be seen as a natural phenomenon with the unaided eye, when the moon blocks the much brighter light of the sun’s photosphere,” Lugger said. “The corona is the upper layer of the sun’s atmosphere composed of extremely hot low-density material, which is a plasma.
“With binoculars, sky watchers may be able to see beautiful structures in the corona, including streamers and loops produced by the sun’s magnetic field. It may also be possible to see the reddish layer of the sun’s chromosphere and reddish arching streamers called solar prominences.”
In addition, Motl said the corona could be larger than average during the 2024 eclipse since the solar surface will be near peak activity — or “solar maximum” — which occurs roughly every 11 years. This cycle is part of the sun’s periodic reversal of its magnetic polarity.
A total of five “naked eye” planets will also be above the horizon as the eclipse passes over Indiana: Mercury, Venus, Mars, Jupiter and Saturn, Pilachowski said. The two highest in the sky — Venus and Jupiter — will be most visible in the greater darkness.
