Why Moon Phase Maps? Most observations of the Moon are made of the terminator, which is the dividing line between night and day. Restricting the maps to each day’s terminator makes them clearer and easier to use. Additionally, lunar features vary greatly depending on the phase, and standard Moon maps cannot account for these changes. For example, many craters that dominate at Full Moon are barely visible at other times. How are the maps used? Use a calendar to establish the number of days since New Moon (a 3 Day Moon, for instance, is three days after New) or estimate the Moon’s age with the naked eye. You might need to use the map for the next or previous day, depending on the terminator position. Maps can be used in the bag for extra protection.