the prime meridian

剑桥词典

the imaginary line from the North Pole to the South Pole that passes through Greenwich in England and marks 0° longitude , from which all other longitudes are measured
本初子午線（從北機到南極的一根假想線，它穿過英格蘭的格林尼治，標示爲經線0°，其他經線以此爲測定標準） 返回 the prime meridian