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Daylight Saving Time (DST)

What is Daylight Saving Time (DST)?

Daylight Saving Time (DST) is the practice of turning the clock ahead as warmer weather approaches and back as it becomes colder again.

The goal of Daylight Saving Time is to make better use of daylight by prolonging the amount of time we can spend outside during daylight hours.

The months when the clock is set ahead and back differ between the Northern and Southern hemispheres.

How does Daylight Saving Time work?

It's important to note that Daylight Saving Time varies somewhat from country to country, and some countries do not observe Daylight Saving Time as part of their time zone.

Examples include American Samoa, Guam, Northern Mariana Islands, U.S. Virgin Islands, Puerto Rico, Japan, India and China.

In most American states, clocks are set forward one hour on the second Sunday in March and back on the first Sunday in November; however, Arizona (except in Navajo Nation) and Hawaii do not observe Daylight Saving Time.

It's colloquially known as spring forward, fall back.

daylight saving time (DST) clock
Daylight Saving Time aims to make better use of daylight by turning the clock ahead with warmer weather and back again with colder weather to prolong the amount of time people can spend outside during daylight hours.

Here are a few of the world's variations in observing Daylight Saving Time:

  • In nonequatorial Brazil, DST starts the first Sunday in November and ends the third Sunday in February.
  • In the European Union, DST starts the last Sunday in March at 1 a.m. Coordinated Universal Time and ends the last Sunday in October at the same time.
  • In Germany, DST starts the last Sunday in March and ends the last Sunday in October.
  • In Russia, the clock is set ahead beginning the last Sunday in March at 2 a.m. local time and set back the last Sunday in October at the same time. Because the clock is already set an hour ahead of standard time, Russians effectively have two more hours of daylight in the summer.
  • In Israel and the area of Palestine, Daylight Saving Time is observed, but the time of change is decided every year. Israel and the Palestinian Authority sometimes have different start and end dates.
  • Jordan has Daylight Saving Time all year.
  • In Australia, DST starts the last Sunday in October and ends the last Sunday in March. However, in Tasmania, DST starts the first Sunday in October, along with New Zealand, and ends the last Sunday in March. New Zealand ends the third Sunday in March.

What is the history of Daylight Saving Time?

Daylight Saving Time was first suggested in 1895 by George Hudson, a New Zealand entomologist who collected insects in his free time. Hudson wanted more daylight hours after work to collect bugs, and Daylight Saving Time was his solution.

The idea of Daylight Saving Time caught on in other countries, especially as energy savings and conservation became a concern during World War II. DST is now used in over 70 countries around the world.

Have there been any changes to Daylight Saving Time since it was created?

Congress passed the U.S. Energy Policy Act of 2005, which mandated time changes to Daylight Saving Time, extending it three weeks earlier in the spring and one week later in the fall.

Starting March 11, 2007, clocks spring ahead an hour on the second Sunday in March and fall back on the first Sunday in November. The assumption behind the change was that it would decrease the need for artificial light sources and, as a result, save energy.

Despite these changes, Daylight Saving Time continues to be a controversial topic. Some argue that the practice is outdated and no longer serves its original purpose. Others claim that Daylight Saving Time helps reduce traffic accidents and crime.

Proponents of DST want to make it permanent year-round to preserve the extra hour of sleep they get during the summer months.

See also: Zulu, wall time, atomic clock and 10,000-year clock.

This was last updated in August 2022

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