Date Line
In the military we set our mission watches and equipment clocks to Z (Zulu) time which civilians called GMT (Greenwich Mean Time) and these days everyone refers to as UTC (Universal Time Coordinated). That makes it easier to determine when something happened. The other ripple in time keeping is the International Date Line which is nominally on the 180° line of longitude between the Americas and Asia, Australia, and the Pacific Island nations.
If we didn’t use Z time when I was flying off of Shemya we would have been flying into tomorrow and returning to yesterday when we landed as the Date Line was just to the West of Shemya.
