No international organization , nor any treaty between nations , has fixed the IDL drawn by cartographers : the 1884 International Meridian Conference explicitly refused to propose or agree to any time zones , stating that they were outside its purview . The conference resolved that the Universal Day , midnight-to-midnight Greenwich Mean Time ( now known as Coordinated Universal Time , or UTC ) , which it did agree to , " shall not interfere with the use of local or standard time where desirable " . From this comes the utility and importance of UTC or " Z ( Zulu ) " time : it permits a single universal reference for time that is valid for all points on the globe at the same moment
International Meridian Conference
International Meridian Conference
International Date Line