摘要：The International Date Line (IDL) is an imaginary line on Earth's surface that marks the boundary where the date changes by one da
The International Date Line (IDL) is an imaginary line on Earth's surface that marks the boundary where the date changes by one day. It is not a straight line but zigzags to avoid passing through populated areas, countries, or island groups, ensuring that nearby regions share the same calendar date as much as possible.
Located roughly along the 180° meridian of longitude (a line that runs from the North Pole to the South Pole), the IDL deviates significantly in some places. For example, it bends eastward around the Aleutian Islands (U.S.) and westward around Fiji and Tonga to accommodate local time zone conventions.
The primary function of the IDL is to resolve the "date confusion" caused by global travel and time zones. When you cross the IDL from west to east (e.g., traveling from Japan to the United States), you subtract one day. Conversely, crossing from east to west (e.g., traveling from the U.S. to Japan) means you add one day. For instance, if it is Monday on the west side of the IDL, crossing to the east side would make it Sunday.
The concept of the International Date Line emerged in the 19th century as global navigation and communication expanded. Before its establishment, sailors often encountered discrepancies in dates after long voyages—some arriving with a date that was a day off from the local date. In 1884, the International Meridian Conference laid the groundwork for the IDL, though its exact path has been adjusted over time based on the needs of countries along its route.
国际日期变更线（IDL）是地球表面上的一条假想线，标志着日期变更一天的界限。它并非一条直线，而是呈锯齿状曲折，以避免穿过人口密集区、国家或岛屿群，确保邻近地区尽可能使用相同的日历日期。
该线大致沿 180° 经线（一条从北极延伸至南极的线）分布，但在部分区域有明显偏离。例如，为适应当地时区惯例，它向东绕过（美国的）阿留申群岛，向西绕过斐济和汤加。
国际日期变更线的主要作用是解决由全球旅行和时区引发的 “日期混乱” 问题。当你从西向东穿越该线时（如从日本前往美国），需减去一天；反之，从东向西穿越时（如从美国前往日本），则需加上一天。例如，若变更线西侧是星期一，穿越至东侧则变为星期日。
随着 19 世纪全球航海和通信的发展，国际日期变更线的概念应运而生。在它确立之前，水手们长途航行后常常遇到日期不符的情况 —— 有些人抵达时的日期与当地日期相差一天。1884 年，国际子午线会议为该线奠定了基础，但其具体路径此后根据沿线国家的需求进行过多次调整。
International Date Line (IDL)音标：/ˌɪntəˈnæʃnəl deɪt laɪn/
中文释义：国际日期变更线
用法说明：专有名词，缩写为 IDL，指地球表面划分日期的假想线，使用时首字母必须大写。Imaginary
音标：/ɪˈmædʒɪnəri/
中文释义：假想的；虚构的
用法说明：形容词，主要修饰抽象或实际不存在的事物，常见搭配如 “imaginary line”（假想线）、“imaginary friend”（假想朋友）、“imaginary world”（虚构世界）。Meridian
音标：/məˈrɪdiən/
中文释义：子午线；经线
用法说明：名词，特指地球表面连接南北两极的半圆线，地理领域常用搭配如 “180° meridian”（180° 经线）、“prime meridian”（本初子午线）。Longitude
音标：/ˈlɒŋɡɪtjuːd/
中文释义：经度
用法说明：名词，与表示 “纬度” 的 “latitude” 相对，用于标识地球表面东西方向的位置，常用表达如 “east longitude”（东经）、“west longitude”（西经）、“latitude and longitude”（经纬度）。Zigzag
音标：/ˈzɪɡzæɡ/
中文释义：v. 曲折前进；n. 之字形
用法说明：作动词时表示 “呈锯齿状移动”，例：“The river zigzags through the valley”（河流蜿蜒穿过山谷）；作名词时指 “之字形的线条或路径”，例：“The path up the hill is a steep zigzag”（上山的路是陡峭的之字形）。Deviate
音标：/ˈdiːvieɪt/
中文释义：v. 偏离；背离
用法说明：不及物动词，通常与介词 “from” 搭配使用，指偏离既定的路线、规则或标准，例：“The plane had to deviate from its original route due to bad weather”（由于天气恶劣，飞机不得不偏离原定航线）。Convention
音标：/kənˈvenʃn/
中文释义：惯例；习俗；会议
用法说明：名词，此处表示 “普遍接受的做法”，如 “time zone convention”（时区惯例）；也可指 “社会习俗”（social convention）或 “正式会议”（international convention）。Discrepancy
音标：/dɪˈskrepənsi/
中文释义：差异；不符
用法说明：名词，指事物之间的不一致或矛盾，常用搭配如 “date discrepancy”（日期不符）、“discrepancy between theory and practice”（理论与实践的差异），复数形式为 “discrepancies”。
来源：哎呀喂英语