First Day of Fall 2016 One of the most frequently misunderstood concepts in science is the reason for Earth’s seasons. As we experience the September equinox today we thought we’d offer a space-based view of what’s going on. Around 6 a.m. local time each day, the Sun, Earth, and any geosynchronous satellite form a right angle, affording a nadir (straight down) view of the terminator, the edge between the shadows of nightfall and the sunlight of dusk and dawn. The shape of this line between night