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 (25 degrees Celsius to 10 degrees C). 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 (minus 13 C to minus 21 degrees C). 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