During the total solar eclipse on Aug. 21, 2017, the moon will completely cover the disk of the sun from Oregon to South Carolina. During this period of “totality,” eclipse observers will likely report feeling a sudden drop in temperature. Just how much does the mercury drop during this celestial event?
During the total solar eclipse on Dec. 9, 1834, the Gettysburg Republican Banner reported that in some places, the eclipse caused the temperature to drop by as much as 28 degrees Fahrenheit, from 78 degrees F to 50 degrees F. During a total solar eclipse on the Norwegian island of Svalbard in March 2015, temperatures dropped from 8 degrees F to minus 7 degrees F.
The change in temperature during a total eclipse will vary based on location and time of year. The temperature change created by the loss of light from the sun’s disk will be similar to the difference between the temperature at midday and the temperature just after sunset, except the change will occur more suddenly, which is why this is often one of the very noticeable effects of a total solar eclipse. [What You’ll See During the 2017 Total Solar Eclipse]
Rick Feinberg, head of media relations for the American Astronomical Society, says people can expect an average drop of about 10 degrees F.
There are written accounts of total solar eclipses going back millennia. And yet, there seems to be lacking any long-term, consistent effort to measure many of the local effects of total solar eclipses — such as the drop in temperature — according to Jay Pasachoff, an astronomer at Williams College who studies eclipses.
Pasachoff and his colleague Marcos Peñaloza-Murillo are working to conduct standardized measurements of many of the local effects of total solar eclipses. The pair produced their first publication on this topic in the Aug. 22, 2016, issue of the journal Philosophical Transactions of the Royal Society of London, where they reported on the change in temperature in Svalbard in…