Shows the areas in sunlight (day) and darkness (night) at the specified date and time or specified declination and noon time vice versa. Illumination map of Earth. What is the Day - Night Terminator? ▫ The day - night terminator is the line where the day side of the earth meets the night side. It is also called the solar terminator. Create a map projection in IDL with a day / night terminator drawn on it.