The April 8th solar eclipse reduced temperature and light for a period in the afternoon of an otherwise mostly sunny day. Sensors in an unheated high tunnel with open end walls at the Pinney Purdue Ag Center, Wanatah, IN, captured the change as the moon covered 96% of the sun (Figure 1). The air temperature dropped 17 degrees, from 82 to 65 °F. Photosynthetically active radiation dropped from 1189 down to 51 µmol /m2/second. Plant growth responds more to temperature and light levels across the whole day than to ups and downs during the day. Growing degree days and daily light integrals (DLI) capture those daily differences (Table 1). On the day of the eclipse, growing degree days in the tunnel were almost the same as the following day (22 vs 21) and higher than other days that weren’t as sunny. The daily light integral on April 8 took a bigger hit: at 24.9 it was only 83% of the DLI for April 9, which was also a sunny day. Other days that were cloudy had even lower DLI: as low as 7 on April 11. The eclipse was a big event for many people, but for plants, it may have been just another spring day.
