Glossary term: International Date Line
Description: The International Date Line is a specific meridian which roughly follows the meridian of longitude 180°. The International Date Line passes north–south between Russia and Alaska, through the Pacific Ocean including parts of Micronesia and Polynesia, and to the east of Australia/New Zealand before reaching the South Pole on Antarctica. The International Date Line marks the boundary where calendar dates change by one. Therefore, regions to the west of the International Date line are one calendar day ahead of regions to the east.
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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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In Other Languages
- Arabic: خط التاريخ الدولي
- German: Datumsgrenze
- French: Ligne internationale de changement de date
- Italian: Linea Internazionale del cambio di Data
- Japanese: 国際日付変更線 (external link)
- Korean: 국제날짜변경선
- Simplified Chinese: 国际日期变更线
- Traditional Chinese: 國際日期變更線
Related Diagrams
International Date Line
Caption: The International Date Line (shown here as a solid line) is a specific meridian which roughly follows the meridian of longitude 180°. The International Date Line passes north–south between Russia and Alaska, through the Pacific Ocean including parts of Micronesia and Polynesia, and to the east of Australia/New Zealand before reaching the South Pole on Antarctica. The International Date Line marks the boundary where calendar dates change by one. Therefore, regions to the west of the International Date line are one calendar day ahead of regions to the east.
The International Date Line does not always exactly follow the meridian of longitude 180°. This is partly to stop some territory of a country falling on the other side of the International Date Line than the rest of that country (the Aleutian Islands in the United States being a good example). Some countries also choose which side of the International Date Line they lie on. Samoa changed which side of the date line it lay on in 2011. At this point the International Date Line was moved to lie to the east of Samoa having previously passed to the west of Samoa.
On the opposite side of the world the dashed line marks the prime meridian (the meridian of longitude 0°). This is a line that passes through the Royal Greenwich Observatory in the UK. All time zones are measure relative to Universal Time which is the zero point for all timezones. The time zones marked at the top of the diagram are the timezones in the shaded regions excluding the effects of daylight savings time.
Credit: Maria Cristina Fortuna/IAU OAE
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
