International Date Line International Date Line The International Date Line (IDL) is an imaginary line of demarcation on the surface of Earth that runs from the North Pole to the South Pole and demarcates the change of one calendar day to the next. It passes through the middle of the Pacific Ocean, roughly following the 180° line of longitude but deviating to pass around some territories and island groups. The IDL is roughly based on the meridian of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the Greenwich meridian. In many places, the IDL follows
USA-180 transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37FM apogee motor. By 5 January 2005, USA-180 was in an orbit with a perigee of , an apogee of , a period of 717.94 minutes, and 54.8 degrees of inclination to the equator. It is used to broadcast the PRN 02 signal, and operates in slot 1 of plane D of the GPS constellation. The satellite has a mass of , and a design life of 10 years. As of 2012 it remains in service. USA-180 USA-180, also known as GPS IIR-13 and GPS SVN-61, is an