It is that time of year again (it happens twice each year) when the relative angle of Earth is perpendicular to the Sun, causing equal incoming solar energy to the Northern and Southern hemispheres, as well as equal day and nighttime. The GOES-13 satellite captured this full disk image of Earth on March 20, 2013, when Earth was at its equinox. The visible imagery sensor on GOES requires sunlight to “see” clouds, and so it provides a useful example of the equinox. In this image the GOES imagery extends to each of the poles since the entire hemisphere is equally lit. After the equinox passes today, the Northern Hemisphere will be more lit than the Southern Hemisphere, causing the seasons. (Note: The Sun in this image is artificially created, though the GOES spacecraft does have sensors continually monitoring the Sun for solar activity.)

Credit: NOAA, GOES Satellite, NASA