Recap of August 21, 2017 Solar Eclipse

Time sequence of the solar eclipse in Springfield, by the University of Illinois at Springfield
Time sequence of the peak of the eclipse in Springfield, courtesy of the University of Illinois at Springfield

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On August 21, 2017, a total solar eclipse was observed in areas from Oregon southeast to South Carolina. The event, the first total eclipse observed in any part of the contiguous 48 states since 1979, saw the longest period of totality (2 minutes 40 seconds) across southern Illinois near Carbondale. Due to the proximity, central and southeast Illinois saw a very significant partial eclipse, with the obscuration of the sun ranging between 93% and 97%.

In a solar eclipse, the moon passes between the sun and the earth, blocking all or part of the sun. In a total solar eclipse like the one on August 21, the sun is completely blocked, causing a period of darkness. In another type of eclipse called an "annular" solar eclipse, the moon is not large enough to completely block the sun, so a ring of light is still observed around it at the peak.

Solar eclipses can be easily seen on visible satellite imagery. In a visible image, the clouds are illuminated by reflected sunlight. The visible image above, taken at 1:30 pm on August 21st, shows a large shadow over the Tennessee Valley into the southeast U.S., where the sunlight has been obscured by the moon's shadow. A loop of such an image will show the shadow quickly moving across the landscape. See below for an example of how this shadow moved across the U.S.

During the height of a solar eclipse, temperatures will usually fall as the amount of incoming solar radiation is reduced. In the area of totality, the drop can be dramatic. In the August 21 eclipse, a drop of 11 degrees was observed at Douglas, WY, 10 degrees at Huntsville, AL, and 8 degrees at Denver. In Carbondale, site of the greatest totality in Illinois, temperatures fell 6 degrees in 25 minutes (90 at 1 pm to 84 at 1:25 pm).

In our area, the greatest fall was observed at the Champaign airport, where temperatures went from 88 degrees at 12:15 pm to 81 at 1:15 pm. Some other observations from around central and southeast Illinois:

Bloomington: 2 degree fall (75 at 1:10 pm to 73 at 1:20 pm)
Danville: 3 degree fall (79 at 12:55 pm to 76 at 1:35 pm)
Decatur: 4 degree fall (84 at 12:30 pm to 79 at 1:20 pm)
Effingham: 6 degree fall (90 at 12:15 pm to 84 at 1:35 pm)
Galesburg: 1 degree fall (74 at 12:55 pm to 73 at 1:15 pm)
Jacksonville: 3 degree fall (79 at 11:55 am to 76 at 1:15 pm)
Lawrenceville: 6 degree fall (90 at 1 pm to 84 at 1:35 pm)
Lincoln: 3 degree fall (77 at 12:50 pm to 74 at 1:25 pm)
Olney: 5 degree fall (90 at 12:20 pm to 85 at 1:35 pm)
Paris: 5 degree fall (86 at 12:55 pm to 81 at 1:35 pm)
Peoria: Steady temperature
Robinson: 6 degree fall (89 at 12:35 pm to 83 at 1:35 pm)
Springfield: 3 degree fall (82 at 12:35 pm to 79 at 1:30 pm)
Taylorville: 3 degree fall (82 at 12:35 pm to 79 at 1:15 pm)

The next partial solar eclipse observable in Illinois will be on October 14, 2023, as an annular eclipse tracks from Oregon southeast through southern Texas into South America. In Illinois, the obscuration will be around 60% from this eclipse.

The next total solar eclipse in the U.S. will be on April 8, 2024, with totality in an area from southern Texas into northern Maine. In an interesting twist, Carbondale will again be in the area of totality, as the eclipse tracks northeast to Indianapolis. In southeast Illinois, totality will be observed northward to the I-70 corridor and as far north as Paris.