TheChamorro Time Zone,[1] formerly theGuam Time Zone, is aUnited States time zone which observesstandard time ten hours ahead ofCoordinated Universal Time (UTC+10:00). The clock time in this zone is based on themean solar time of the150th meridian east of theGreenwich Observatory.
The zone includes theU.S. territories ofGuam and theNorthern Mariana Islands, where theChamorro people are the original inhabitants. SinceDaylight Saving Time (DST) is not observed anywhere in this zone, the time is always known asChamorro Standard Time (ChST).
The zone is two hours behindWake Island Time Zone and 15 hours ahead of North AmericanEastern Time Zone. As of March 19, 2024 it is the easternmost (farthest ahead) time zone shown on the U.S. government's time.gov webpage. AlthoughWake,Howland andBaker Islands are U.S. territories in more easterly time zones (that are not shown), they are uninhabited.
Chamorro Standard Time shares the same time asAustralian Eastern Standard Time. The State ofQueensland also does not observe DST, so the Commonwealth of the Northern Mariana Islands (CNMI), Guam and Queensland are on the same time year round.
Until the end of 1844,Guam andMariana Islands belonged toCaptaincy General of the Philippines, which followed the date of the western hemisphere on their island, placing them on the eastern side of theInternational Date Line (IDL). At the end of Monday, December 30, 1844, both Guam and Mariana Islands continued directly to Wednesday, January 1, 1845, effectively removing Tuesday, December 31, 1844 from the calendar to follow the eastern hemisphere on the west side of the IDL and realign themselves from American to Asian dates.[citation needed]
Before time zones were introduced, every place used local observation of the sun to set its clocks, which meant that every location used a different local mean time based on its longitude. For example, Hagåtña, the capital of Guam at the time, at longitude 144°45′E, had a local time equivalent to GMT-14:21 under the date of the western hemisphere and GMT+09:39 under the eastern hemisphere.[citation needed]
In 1901, "Guam Standard Time" was established within the United States as GMT+10:00.[citation needed]
The U.S. Congress formally created Chamorro Standard Time by federal Public Law 106-564 on December 23, 2000. Previously,Guam Standard Time existed per territorial Public Law 5-25 (1959).[2] This statute is still on the territorial law books, although it is preempted by the federal law.[citation needed]
The Northern Mariana Islands, as part of theTrust Territory of the Pacific Islands, were not part of any American time zone prior to becoming a U.S. Commonwealth on January 1, 1978. Being directly north of Guam, however, they observed the same time.[citation needed]