The terminator is the line that separates day and night on Earth, also known as the “grey line” or “twilight zone.” Due to atmospheric refraction, this line is not sharp but fuzzy, with sunlight bending by about half a degree. Contrary to popular belief, more of Earth’s surface is illuminated by sunlight than is in darkness at any given time. The shape of the terminator changes with the seasons, being parallel to Earth’s axis during equinoxes and at a 23.5-degree angle during solstices. This seasonal variation is evident in a dataset that shows the terminator throughout 2007.
