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Timezones

The timezone CHST in Guam

Timezones are always computed by their difference to UTC, the "Universal Time Coordinated". In Guam exists only a single tonezone at UTC+10. E.g. New York is currently at UTC-5 in Eastern Time, so the time difference between New York and Guam is 15 hours.
Guam has no time difference between summer and winter. A daylight saving time doesn't exist.
Back to overview: Guam

Only 1 nationwide time zone

UTC+10
Standard time:Chamorro Standard Time (CHST)
Daylight saving time:discontinued 1977

Guam has an east-west extension of 0.2 degrees of longitude. Given the country's location in Micronesia, this corresponds to about 25 kilometers. With such a small extent the course of the sun at different positions in the country hardly matters. The position of the sun in the west of the country deviates from that in the east only about 55 seconds. This means the sun rises and sets 55 seconds later in the west than in the east.
Timezones
The Chamorro Standard Time also applies in Northern Marianas.

No more daylight saving time in Guam

Due to the sun's orbit around the equator, the days are longer in summer (June to September in the northern hemisphere). Countries that switch to daylight saving time in the summer months align the daylight phase with the human rhythm. Unused bright morning hours are thus shifted into the evening (more information on daylight saving time here).
Due to its proximity to the equator, the impact in Guam would not be particularly large. Hagåtña is located just 1,500 km from the equator. A day in midsummer would then not last from 05:54 to 18:51, but from 06:54 to 19:51. The effect would be quite noticeable in the evening, but the sun rising later in the morning falls at a time when many people are already awake. Thus, in 1977, the decision was made to finally abandon daylight saving time in Guam.

Changes in Daylight Saving Times

In Guam Daylight Saving Time has been observed since 1959 until 08/28/1977.
Guam: Sunrise + sunsetTimes for sunrise and sunset in GuamTimes of sunrise and sunset for the most important cities in Guam and the avg. length of daylight per month
Countries with DSTAll Countries with DSTA summary of all countries that currently observe Daylight Saving Time with further info on introductions and upcoming changes.
United States of America: EarthquakeRecent earthquakes and their magnitudes in the United StatesEarthquakes and their intensities in the United States of America