International Date Line
The line of longitude located at 180 Degrees East or West where the date changes by a day. West of the line it is one day later than east of the line.
Longitude
The location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude. The distance between lines of longitude are greater at the equator and smaller at the higher latitudes, intersecting at the earth’s North and South Poles. Time zones are correlated to longitude.
Day
Considered a basic unit of time as defined by the earth’s motion. It represents the time needed for one complete revolution of the earth about its own axis. Also know as a sidereal day, it is approximately equal to 23 hours, 56 minutes, and 4.09 seconds.