시간대
Time zone표준 시간대는 법적, 상업적, 사회적 목적을 위해 통일된 표준 시간을 준수하는 영역입니다.시간대는 경도를 엄격히 따르는 대신 국가와 그 지역 간의 경계를 따르는 경향이 있는데, 이는 통신 빈도가 높은 지역이 같은 시간을 유지하는 것이 편리하기 때문이다.
모든 시간대는 UTC-12:00 ~ UTC+14:00 범위의 Coordinated Universal Time(UTC; 협정 세계시) 오프셋으로 정의됩니다.오프셋은 보통 정수 시간이지만, 인도, 사우스 오스트레일리아, 네팔과 같이 일부 구역은 추가로 30분에서 45분씩 오프셋됩니다.
위도가 높은 일부 지역은 1년 중 절반 정도 여름 시간을 사용하며, 일반적으로 봄과 여름 동안 현지 시간에 1시간을 더한다.
UTC 오프셋 목록
다음 표에서는 DST가 적용되지 않을 때 여름 시간(DST)을 사용하는 위치를 UTC 오프셋에 나타냅니다.DST가 발효되면 대략 봄과 여름 동안 UTC 오프셋이 1시간 증가합니다(로드 하우 아일랜드에서는 30분 증가).예를 들어 DST 기간 동안 캘리포니아는 UTC-07:00를 준수하고 영국은 UTC+01:00를 준수합니다.
역사
하늘에서 태양의 겉으로 보이는 위치, 즉 태양 시간은 지구의 구형 모양 때문에 위치에 따라 다릅니다.이 변화는 모든 경도의 4분에 해당하기 때문에 예를 들어 런던이 태양 정오가 되면 브리스톨은 태양 정오가 되기 10분 전이고,[5] 이는 서쪽으로 약 2.5도입니다.
1675년에 설립된 그리니치의 왕립 천문대는 영국의 각 장소가 다른 시간을 유지하는 동안 표준 기준 시간을 제공하면서, 선원들이 바다에서 경도를 결정하는 데 도움을 주기 위해 그 위치의 평균 태양시인 그리니치 표준시를 설정했다.
기차 시간
19세기에는 교통과 통신이 발달하면서 각 지역에서 태양 시간을 관측하는 것이 점점 더 불편해졌다.1840년 11월, Great Western 철도는 [6]휴대용 크로노미터로 유지되는 GMT를 사용하기 시작했다.이 관행은 곧 영국의 다른 철도 회사들에 의해 따라졌고 철도 시간으로 알려지게 되었다.
1852년 8월 23일 경, 왕립 천문대에서 전보로 시간 신호가 처음 전송되었다.1855년까지 영국의 공공 시계 중 98%가 GMT를 사용했지만, 1880년 8월 2일까지는 섬의 법정 시간이 되지 않았다.이 시기의 일부 영국 시계에는 현지 시간용과 [7]GMT용 두 분침이 있습니다.
1868년 11월 2일, 당시 영국령 뉴질랜드 식민지는 [8]식민지 전체에서 관측되는 표준 시간을 공식적으로 채택했습니다.GMT보다 11시간 30분 빠른 그리니치 동쪽 경도 172°30에 근거하고 있습니다.이 표준은 뉴질랜드 [9]표준시로 알려져 있습니다.
19세기 북미 철도의 시간 기록은 복잡했다.각 철도는 일반적으로 본사 또는 가장 중요한 종착역의 현지 시간을 기준으로 자체 표준 시간을 사용했으며, 철도의 열차 시간표는 자체 시간을 사용하여 발행되었습니다.몇몇 철도들이 운행하는 교차로에는 각각의 철도마다 시계가 있었고,[10] 각각 다른 시간을 보여주었다.
찰스 F. 다우드는 1863년 경 북미 철도의 시간당 표준 시간대 시스템을 제안했지만, 그는 그 문제에 대해 아무것도 발표하지 않았고 1869년까지 철도 관계자들과 상의하지 않았다.1870년에 그는 북쪽과 남쪽 경계를 가진 네 개의 이상적인 시간대를 제안했는데, 첫 번째 시간대는 워싱턴 D.C.를 중심으로 했지만, 1872년까지 첫 번째 시간대는 애팔래치아 산맥의 부분과 같은 자연적인 경계와 함께 그리니치 서쪽 자오선 75°에 집중되었다.다우드의 시스템은 북미 철도에서 결코 받아들여지지 않았다.대신, 미국과 캐나다 철도는 William F.에 의해 제안된 버전을 시행했다.여행자 공식 철도 [11]안내서의 편집자인 앨런.그 시간대의 경계는 종종 주요 도시에 있는 기차역을 통과했다.예를 들어 동부 표준시와 중부 표준시 사이의 경계선은 디트로이트, 버팔로, 피츠버그, 애틀랜타 및 찰스턴을 통과합니다.1883년 11월 18일 일요일, "두 낮의 날"[12]이라고도 불리며, 각 시간대 내에서 표준 시간 정오에 도달하면서 각 기차역 시계가 재설정되었다.
북미 지역은 식민지 간, 동부, 중부, 산악, 태평양으로 명명되었다.1년 이내에 인구 10,000명 이상의 모든 도시(약 200개 도시)의 85%가 표준 [13]시간을 사용했다.눈에 띄는 예외는 디트로이트로, 1900년까지 현지 시간을 유지하다가 1915년 5월 EST 조례가 제정되기 전에 중앙 표준시, 현지 표준시, 동부 표준시(EST)를 시도했고 1916년 8월 일반 투표에 의해 비준되었다.시대의 혼란은 1918년 3월 19일 미국 의회에서 표준 시간대가 공식적으로 채택되면서 끝이 났다.
세계 표준 시간대
이탈리아 수학자 퀴리코 필로판티는 1858년에 출판된 그의 책 미란다에서 세계적인 시간대의 개념을 소개했습니다.그는 로마의 자오선을 중심으로 한 24시간 시간대를 제안했는데, 이것을 "종적 날"이라고 불렀다.그는 또한 천문학과 전신에 사용되는 보편적인 시간을 제안했다.하지만 그의 책은 그가 [14][15]죽은 후 오랫동안 관심을 끌지 못했다.
스코틀랜드 태생의 캐나다인 Sandford Fleming 경은 1876년에 세계 표준시 체계를 제안했습니다. Sandford Fleming © 세계 표준시 발명가를 참조하십시오.이 제안은 세계를 A-Y(건너뛰기 J)로 표기된 24개의 시간대로 나누었으며, 각각의 시간대는 경도 15도를 포함하고 있다.각 존 내의 모든 클럭은 다른 클럭과 같은 시각으로 설정되지만 인접 [16]존의 클럭과는 1시간 차이가 납니다.그는 국제 Meridian Conference를 포함한 여러 국제 컨퍼런스에서 자신의 시스템을 주장했고, 그곳에서 어느 정도 검토되었다.이 시스템은 직접적으로 채택되지는 않았지만, 일부 지도는 플레밍의 [17]시스템과 유사하게 세계를 24개의 시간대로 나누고 그들에게 문자를 할당한다.
약 1900년까지, 지구상에 거의 모든 거주 지역이 표준 시간대를 채택했지만, 그들 중 일부만이 GMT로부터의 시간 간격을 사용했다. 많은 사람들은 GMT에 대한 언급 없이 지역 천문 관측소의 시간을 나라 전체에 적용했다. 모든 시간대가 GMT나 좌표로부터 표준 시간대를 기반으로 하기까지는 수십 년이 걸렸다.d 세계시(UTC)이란, 인도, 호주 일부와 같은 일부 국가는 30분 간격으로 시간대를 설정했지만, 1929년까지 대부분의 국가는 시간대를 도입했다.네팔은 1986년 [18]UTC+05:45로 약간 변경되어 표준 오프셋을 채택한 마지막 국가이다.
현재 모든 국가가 세속적인 목적을 위해 표준 시간대를 사용하고 있지만, 모든 국가가 원래 생각대로 표준 시간대를 적용하는 것은 아니다.일부 국가 및 구역에서는 표준 시간에서 30분 또는 15분 편차를 사용합니다.중국과 인도와 같은 일부 국가는 영토의 범위가 이상적인 경도 15°를 1시간 동안 훨씬 초과하더라도 단일 시간대를 사용한다. 스페인이나 아르헨티나와 같은 다른 국가는 표준 시간 기준 오프셋을 사용하지만 반드시 지리적 위치에 따라 결정되는 것은 아니다.일부 지역에서는 그 결과가 지역 시민들의 삶에 영향을 미칠 수 있으며,[19] 극단적인 경우에는 중국의 서부지역과 같은 더 큰 정치적 문제에 기여한다.11개의 시간대가 있는 러시아에서는 2010년에[20][21] 2개의 시간대가 삭제되었다가 [22]2014년에 복구되었다.
표기법
ISO 8601
ISO 8601은 국제표준화기구가 정한 표준으로, 날짜 및 시간을 텍스트 형식으로 표현하는 방법을 정의하며,[23] 여기에는 표준 시간대를 나타내는 규격이 포함됩니다.
시각이 Coordinated Universal Time(UTC; 좌표 세계시)에 있는 경우, 시간 직후에 공백 없이 "Z"가 추가됩니다."Z"는 제로 UTC 오프셋의 존 지정자입니다.따라서 "09:30 UTC"는 "09:30Z" 또는 "0930Z"로 표시됩니다.마찬가지로 "14:45:15 UTC"는 "14:45:15Z" 또는 "144515Z"[24]로 표기됩니다.UTC 시간은 "Zulu"[24]라는 문자의 발음 알파벳 코드 단어이기 때문에 "Zulu"라고 불리기도 합니다.
UTC로부터의 오프셋은 ±hh:mm, ±hmm 또는 ±hhhm 또는 ±hhhh 형식으로 작성됩니다(UTC보다 몇 시간 앞 또는 뒤).예를 들어, 설명되는 시간이 UTC보다 1시간 빠른 경우(동절기 독일의 시간 등), 존 지정자는 "+01:00", "+0100", 또는 단순히 "+01"이 됩니다.이 시간대의 숫자 표현은 알파벳 시간대 약어(또는 위와 같이 "Z")가 추가되는 것과 동일한 방식으로 현지 시간에 추가됩니다.UTC로부터의 오프셋은 여름 시간(예: 북미 중앙 시간대에 있는 시카고의 시간 오프셋)에 따라 변화하며, 겨울(중앙 표준시)은 -06:00, 여름(중앙 여름 시간)[25]은 -05:00입니다.
약어
표준 시간대는 종종 "EST", "WST" 및 "CST"와 같은 영문자 약어로 표시되지만 국제 표준 ISO 8601의 일부가 아닙니다.이러한 지정은 애매할 수 있습니다.예를 들어, 「CST」는 (북미) 중부 표준시(UTC-06:00), 쿠바 표준시(UTC-05:00), 중국 표준시(UTC+08:00)를 의미할 수 있습니다.또, ACST(호주 중부 UTC+08:00)에서도 널리 사용되고 있습니다.
변환
시간대 간 변환이 관계를 준수합니다.
- "구역 A의 시간" - "구역 A의 UTC 오프셋" = "구역 B의 시간" - "구역 B의 UTC 오프셋",
방정식의 각 변이 UTC와 같은 값이다.
변환 방정식은 다음과 같이 재배열할 수 있습니다.
- "구역 B의 시간" = "구역 A의 시간" - "구역 A의 UTC 오프셋" + "구역 B의 UTC 오프셋"
예를 들어, 뉴욕 증권거래소는 09:30(EST, UTC 오프셋= -05:00)에 개장합니다.캘리포니아(PST, UTC 오프셋= -08:00) 및 인도(IST, UTC 오프셋= +05:30)에서는 뉴욕 증권거래소가 다음 날짜에 개장합니다.
- 캘리포니아 시간 = 09:30 - (-05:00) + (-08:00) = 06:30;
- 인도 시간 = 09:30 - (-05:00) + (+05:30) = 20:00입니다.
이러한 계산은 서머 타임으로의 전환이나 서머 타임으로부터의 전환에 수반해, 그 영역의 UTC 오프셋이 UTC 시각의 함수가 되기 때문에, 한층 더 복잡해집니다.
시차에 따라 날짜도 다를 수 있습니다.예를 들어 이집트에서는 월요일 22:00(UTC+02:00)이면 파키스탄에서는 화요일 01:00(UTC+05:00)입니다.
"Time of days by zone" 표는 서로 다른 구역 간의 시간 관계에 대한 개요를 제공합니다.
시간대별 구역별 | ||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
UTC 오프셋 | 월요일. | |||||||||||||||||||||||
UTC−12:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 |
UTC−11:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 |
UTC−10:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 |
UTC−09:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 |
UTC−09:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 |
UTC−08:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 |
UTC−07:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 |
UTC−06:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 |
UTC−05:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 |
UTC−04:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 |
UTC−03:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 |
UTC−03:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 |
UTC−02:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 |
UTC−02:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 |
UTC−01:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 |
UTC±00:00:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 |
UTC+01:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 |
UTC+02:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 |
UTC+03:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 |
UTC+03:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 |
UTC+04:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 |
UTC+04:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 |
UTC+05:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 |
UTC+05:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 |
UTC+05:45 | 17:45 | 18:45 | 19:45 | 20:45 | 21:45 | 22:45 | 23:45 | 00:45 | 01:45 | 02:45 | 03:45 | 04:45 | 05:45 | 06:45 | 07:45 | 08:45 | 09:45 | 10:45 | 11:45 | 12:45 | 13:45 | 14:45 | 15:45 | 16:45 |
UTC+06:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 |
UTC+06:30 | 18:30 | 19:30 | 20:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 |
UTC+07:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 |
UTC+08:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 |
UTC+08:45 | 20:45 | 21:45 | 22:45 | 23:45 | 00:45 | 01:45 | 02:45 | 03:45 | 04:45 | 05:45 | 06:45 | 07:45 | 08:45 | 09:45 | 10:45 | 11:45 | 12:45 | 13:45 | 14:45 | 15:45 | 16:45 | 17:45 | 18:45 | 19:45 |
UTC+09:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 |
UTC+09:30 | 21:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 |
UTC+10:00 | 22:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 |
UTC+10:30 | 22:30 | 23:30 | 00:30 | 01:30 | 02:30 | 03:30 | 04:30 | 05:30 | 06:30 | 07:30 | 08:30 | 09:30 | 10:30 | 11:30 | 12:30 | 13:30 | 14:30 | 15:30 | 16:30 | 17:30 | 18:30 | 19:30 | 20:30 | 21:30 |
UTC+11:00 | 23:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 |
UTC+12:00 | 00:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 |
UTC+12:45 | 00:45 | 01:45 | 02:45 | 03:45 | 04:45 | 05:45 | 06:45 | 07:45 | 08:45 | 09:45 | 10:45 | 11:45 | 12:45 | 13:45 | 14:45 | 15:45 | 16:45 | 17:45 | 18:45 | 19:45 | 20:45 | 21:45 | 22:45 | 23:45 |
UTC+13:00 | 01:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 |
UTC+13:45 | 01:45 | 02:45 | 03:45 | 04:45 | 05:45 | 06:45 | 07:45 | 08:45 | 09:45 | 10:45 | 11:45 | 12:45 | 13:45 | 14:45 | 15:45 | 16:45 | 17:45 | 18:45 | 19:45 | 20:45 | 21:45 | 22:45 | 23:45 | 00:45 |
UTC+14:00 | 02:00 | 03:00 | 04:00 | 05:00 | 06:00 | 07:00 | 08:00 | 09:00 | 10:00 | 11:00 | 12:00 | 13:00 | 14:00 | 15:00 | 16:00 | 17:00 | 18:00 | 19:00 | 20:00 | 21:00 | 22:00 | 23:00 | 00:00 | 01:00 |
UTC offset | Tuesday | Wednesday |
Nautical time zones
Since the 1920s, a nautical standard time system has been in operation for ships on the high seas. As an ideal form of the terrestrial time zone system, nautical time zones consist of gores of 15° offset from GMT by a whole number of hours. A nautical date line follows the 180th meridian, bisecting one 15° gore into two 7.5° gores that differ from GMT by ±12 hours.[27][28][29]
However, in practice each ship may choose what time to observe at each location. Ships may decide to adjust their clocks at a convenient time, usually at night, not exactly when they cross a certain longitude.[30] Some ships simply remain on the time of the departing port during the whole trip.[31]
Skewing of time zones
Ideal time zones, such as nautical time zones, are based on the mean solar time of a particular meridian located in the middle of that zone with boundaries located 7.5 degrees east and west of the meridian. In practice, however, many time zone boundaries are drawn much farther to the west, and some countries are located entirely outside their ideal time zones.
For example, even though the Prime Meridian (0°) passes through Spain and France, they use the mean solar time of 15 degrees east (Central European Time) rather than 0 degrees (Greenwich Mean Time). France previously used GMT, but was switched to CET (Central European Time) during the German occupation of the country during World War II and did not switch back after the war.[32] Similarly, prior to World War II, the Netherlands observed "Amsterdam Time", which was twenty minutes ahead of Greenwich Mean Time. They were obliged to follow German time during the war, and kept it thereafter. In the mid-1970s the Netherlands, as other European states, began observing daylight saving (summer) time.
One reason to draw time zone boundaries far to the west of their ideal meridians is to allow the more efficient use of sunlight.[33] Some of these locations also use daylight saving time (DST), further increasing the difference to local solar time. As a result, in summer, solar noon in the Spanish city of Vigo occurs at 14:41 clock time. This westernmost area of continental Spain never experiences sunset before 18:00 clock time, even in winter, despite lying 42 degrees north of the equator.[34] Near the summer solstice, Vigo has sunset times after 22:00, similar to those of Stockholm, which is in the same time zone and 17 degrees farther north. Stockholm has much earlier sunrises, though.[35]
A more extreme example is Nome, Alaska, which is at 165°24′W longitude – just west of center of the idealized Samoa Time Zone (165°W). Nevertheless, Nome observes Alaska Time (135°W) with DST so it is slightly more than two hours ahead of the sun in winter and over three in summer.[36] Kotzebue, Alaska, also near the same meridian but north of the Arctic Circle, has two sunsets on the same day in early August, one shortly after midnight at the start of the day, and the other shortly before midnight at the end of the day.[37]
China extends as far west as 73°E, but all parts of it use UTC+08:00 (120°E), so solar "noon" can occur as late as 15:00 in western portions of China such as Xinjiang.[38] The Afghanistan-China border marks the greatest terrestrial time zone difference on Earth, with a 3.5 hour difference between Afghanistan's UTC+4:30 and China's UTC+08:00.
Daylight saving time
Many countries, and sometimes just certain regions of countries, adopt daylight saving time (DST), also known as summer time, during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn ("spring forward", "fall back"). Modern DST was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal. Despite controversy, many countries have used it off and on since then; details vary by location and change occasionally. Countries around the equator usually do not observe daylight saving time, since the seasonal difference in sunlight there is minimal.
Computer systems
Many computer operating systems include the necessary support for working with all (or almost all) possible local times based on the various time zones. Internally, operating systems typically use UTC as their basic time-keeping standard, while providing services for converting local times to and from UTC, and also the ability to automatically change local time conversions at the start and end of daylight saving time in the various time zones. (See the article on daylight saving time for more details on this aspect).
Web servers presenting web pages primarily for an audience in a single time zone or a limited range of time zones typically show times as a local time, perhaps with UTC time in brackets. More internationally oriented websites may show times in UTC only or using an arbitrary time zone. For example, the international English-language version of CNN includes GMT and Hong Kong Time,[39] whereas the US version shows Eastern Time.[40] US Eastern Time and Pacific Time are also used fairly commonly on many US-based English-language websites with global readership. The format is typically based in the W3C Note "datetime".
Email systems and other messaging systems (IRC chat, etc.)[41] time-stamp messages using UTC, or else include the sender's time zone as part of the message, allowing the receiving program to display the message's date and time of sending in the recipient's local time.
Database records that include a time stamp typically use UTC, especially when the database is part of a system that spans multiple time zones. The use of local time for time-stamping records is not recommended for time zones that implement daylight saving time because once a year there is a one-hour period when local times are ambiguous.
Calendar systems nowadays usually tie their time stamps to UTC, and show them differently on computers that are in different time zones. That works when having telephone or internet meetings. It works less well when travelling, because the calendar events are assumed to take place in the time zone the computer or smartphone was on when creating the event. The event can be shown at the wrong time. For example, if a New Yorker plans to meet someone in Los Angeles at 9 AM, and makes a calendar entry at 9 AM (which the computer assumes is New York time), the calendar entry will be at 6 AM if taking the computer's time zone. There is also an option in newer versions of Microsoft Outlook to enter the time zone in which an event will happen, but often not in other calendar systems. Calendaring software must also deal with daylight saving time (DST). If, for political reasons, the begin and end dates of daylight saving time are changed, calendar entries should stay the same in local time, even though they may shift in UTC time. In Microsoft Outlook, time stamps are therefore stored and communicated without DST offsets.[42] Hence, an appointment in London at noon in the summer will be represented as 12:00 (UTC+00:00) even though the event will actually take place at 13:00 UTC. In Google Calendar, calendar events are stored in UTC (although shown in local time) and might be changed by a time-zone changes,[43] although normal daylight saving start and end are compensated for (similar to much other calendar software).
Operating systems
Unix
Most Unix-like systems, including Linux and Mac OS X, keep system time in time_t format, representing the number of seconds (excluding leap seconds) that have elapsed since 00:00:00 Coordinated Universal Time (UTC) on Thursday, January 1, 1970.[44] By default the external representation is as UTC (Coordinated Universal Time), though individual processes can specify time zones using the TZ environment variable.[45] This allows users in multiple time zones to use the same computer, with their respective local times displayed correctly to each user. Time zone information most commonly comes from the IANA time zone database. In fact, many systems, including anything using the GNU C Library, can make use of this database.
Microsoft Windows
Windows-based computer systems prior to Windows 2000 used local time, but Windows 2000 and later can use UTC as the basic system time.[46] The system registry contains time zone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone. Interaction with the user normally uses local time, and application software is able to calculate the time in various zones. Terminal Servers allow remote computers to redirect their time zone settings to the Terminal Server so that users see the correct time for their time zone in their desktop/application sessions. Terminal Services uses the server base time on the Terminal Server and the client time zone information to calculate the time in the session.
Programming languages
Java
While most application software will use the underlying operating system for time zone information, the Java Platform, from version 1.3.1, has maintained its own time zone database. This database is updated whenever time zone rules change. Oracle provides an updater tool for this purpose.[47]
As an alternative to the time zone information bundled with the Java Platform, programmers may choose to use the Joda-Time library.[48] This library includes its own time zone data based on the IANA time zone database.[49]
As of Java 8 there is a new date and time API that can help with converting time zones. Java 8 Date Time
JavaScript
Traditionally, there was very little in the way of time zone support for JavaScript. Essentially the programmer had to extract the UTC offset by instantiating a time object, getting a GMT time from it, and differencing the two. This does not provide a solution for more complex daylight saving variations, such as divergent DST directions between northern and southern hemispheres.
ECMA-402, the standard on Internationalization API for JavaScript, provides ways of formatting Time Zones.[50] However, due to size constraint, some implementations or distributions do not include it.[51]
Perl
The DateTime object in Perl supports all time zones in the Olson DB and includes the ability to get, set and convert between time zones.[52]
PHP
The DateTime objects and related functions have been compiled into the PHP core since 5.2. This includes the ability to get and set the default script time zone, and DateTime is aware of its own time zone internally. PHP.net provides extensive documentation on this.[53] As noted there, the most current time zone database can be implemented via the PECL timezonedb.
Python
The standard module datetime included with Python stores and operates on the time zone information class tzinfo. The third party pytz module provides access to the full IANA time zone database.[54] Negated time zone offset in seconds is stored time.timezone and time.altzone attributes. From Python 3.9, the zoneinfo module introduces timezone management without need for third party module.[55]
Smalltalk
Each Smalltalk dialect comes with its own built-in classes for dates, times and timestamps, only a few of which implement the DateAndTime and Duration classes as specified by the ANSI Smalltalk Standard. VisualWorks provides a TimeZone class that supports up to two annually recurring offset transitions, which are assumed to apply to all years (same behavior as Windows time zones). Squeak provides a Timezone class that does not support any offset transitions. Dolphin Smalltalk does not support time zones at all.
For full support of the tz database (zoneinfo) in a Smalltalk application (including support for any number of annually recurring offset transitions, and support for different intra-year offset transition rules in different years) the third-party, open-source, ANSI-Smalltalk-compliant Chronos Date/Time Library is available for use with any of the following Smalltalk dialects: VisualWorks, Squeak, Gemstone, or Dolphin.[56]
Time in outer space
Orbiting spacecraft may experience many sunrises and sunsets, or none, in a 24-hour period. Therefore, it is not possible to calibrate the time with respect to the Sun and still respect a 24-hour sleep/wake cycle. A common practice for space exploration is to use the Earth-based time of the launch site or mission control, synchronizing the sleeping cycles of the crew and controllers. The International Space Station normally uses Greenwich Mean Time (GMT).[57][58]
Timekeeping on Mars can be more complex, since the planet has a solar day of approximately 24 hours and 40 minutes, known as a sol. Earth controllers for some Mars missions have synchronized their sleep/wake cycles with the Martian day, because solar-powered rover activity on the surface was tied to periods of light and dark.[59]
See also
- Daylight saving time
- ISO 8601
- Jet lag
- Lists of time zones
- Metric time
- Time by country
- Time in Europe
- Time zone abolition
- World clock
- Template:Sunclock[60]
- International Date Line
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- ^ "Map Maker Sun Clock". mapmaker.com. Retrieved July 9, 2022.
Further reading
- Biswas, Soutik (February 12, 2019). "How India's single time zone is hurting its people". BBC News. Retrieved February 12, 2019.
- Maulik Jagnani, economist at Cornell University (January 15, 2019). "PoorSleep: Sunset Time and Human Capital Production" (Job Market Paper). Retrieved February 12, 2019.
- "Time Bandits: The countries rebelling against GMT" (Video). BBC News. August 14, 2015. Retrieved February 12, 2019.
- "How time zones confused the world". BBC News. August 7, 2015. Retrieved February 12, 2019.
- Lane, Megan (May 10, 2011). "How does a country change its time zone?". BBC News. Retrieved February 12, 2019.
- "A brief history of time zones" (Video). BBC News. March 24, 2011. Retrieved February 12, 2019.
- The Time Zone Information Format (TZif). doi:10.17487/RFC8536. RFC 8536.
External links
- Media related to Time zones at Wikimedia Commons