Day/Night Terminator is a new layer item in ArcGIS Living Atlas that lets users include a visualization of the current day/night cycle in their maps and apps.
Day/Night Terminator is updated every 10 minutes using the Esri Live Feeds Methodology and computes the approximate location of the Sun, perpendicular to the planet, using the current UTC date and time.

For more information, see Introducing Day-Night Terminator.