<P> Due to the movement of Earth 's tectonic plates , the line of 0 ° longitude along the surface of the Earth has slowly moved toward the west from this shifted position by a few centimetres ; that is , towards the Airy Transit Circle ( or the Airy Transit Circle has moved toward the east , depending on your point of view ) since 1984 ( or the 1960s ) . With the introduction of satellite technology , it became possible to create a more accurate and detailed global map . With these advances there also arose the necessity to define a reference meridian that , whilst being derived from the Airy Transit Circle , would also take into account the effects of plate movement and variations in the way that the Earth was spinning . As a result , the International Reference Meridian was established and is commonly used to denote Earth 's prime meridian ( 0 ° longitude ) by the International Earth Rotation and Reference Systems Service , which defines and maintains the link between longitude and time . Based on observations to satellites and celestial compact radio sources ( quasars ) from various coordinated stations around the globe , Airy 's transit circle drifts northeast about 2.5 centimetres per year relative to this Earth - centred 0 ° longitude . Circa 1999 the international reference meridian ( IRM ) passed 5.31 arcseconds east of Airy 's meridian or 102.5 metres ( 336.3 feet ) at the latitude of the Royal Observatory , Greenwich , London . It is also the reference meridian of the Global Positioning System operated by the United States Department of Defense , and of WGS84 and its two formal versions , the ideal International Terrestrial Reference System ( ITRS ) and its realization , the International Terrestrial Reference Frame ( ITRF ) . A current convention on the Earth uses the opposite of the IRM as the basis for the International Date Line . </P>
<P> Due to the movement of Earth 's tectonic plates , the line of 0 ° longitude along the surface of the Earth has slowly moved toward the west from this shifted position by a few centimetres ; that is , towards the Airy Transit Circle ( or the Airy Transit Circle has moved toward the east , depending on your point of view ) since 1984 ( or the 1960s ) . With the introduction of satellite technology , it became possible to create a more accurate and detailed global map . With these advances there also arose the necessity to define a reference meridian that , whilst being derived from the Airy Transit Circle , would also take into account the effects of plate movement and variations in the way that the Earth was spinning . As a result , the International Reference Meridian was established and is commonly used to denote Earth 's prime meridian ( 0 ° longitude ) by the International Earth Rotation and Reference Systems Service , which defines and maintains the link between longitude and time . Based on observations to satellites and celestial compact radio sources ( quasars ) from various coordinated stations around the globe , Airy 's transit circle drifts northeast about 2.5 centimetres per year relative to this Earth - centred 0 ° longitude . Circa 1999 the international reference meridian ( IRM ) passed 5.31 arcseconds east of Airy 's meridian or 102.5 metres ( 336.3 feet ) at the latitude of the Royal Observatory , Greenwich , London . It is also the reference meridian of the Global Positioning System operated by the United States Department of Defense , and of WGS84 and its two formal versions , the ideal International Terrestrial Reference System ( ITRS ) and its realization , the International Terrestrial Reference Frame ( ITRF ) . A current convention on the Earth uses the opposite of the IRM as the basis for the International Date Line . </P>
the meridian opposite of earth 's prime meridian ( 0 ° longitude ) is called
the meridian opposite of earth 's prime meridian ( 0 ° longitude ) is called
International Date Line
International Date Line