U.S. and Canadian citizens lose some sleep tonight as the clock is turned forward one hour, marking the beginning of daylight saving time.
Most U.S. states will return to daylight saving time at 2 a.m. tomorrow, the U.S. National Institute of Standards and Technology said on its website. The change, which adds an hour of daylight in the evening, is commonly observed in the Northern Hemisphere. Canada follows the same standard as the U.S., according to the National Research Council Canada.
Daylight saving time begins on the second Sunday in March and ends on the first Sunday in November. The time change was first observed in the U.S. in 1918.
The practice isn’t mandatory. Hawaii, most of Arizona and the U.S. territories of American Samoa, Guam, Puerto Rico and the U.S. Virgin Islands don’t observe the time change.
Mexico also follows daylight saving time, though the changes are made on the first Sunday in April and the last Sunday in October.