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About Daylight Saving Time

See The World Clock for current times and places observing daylight saving time (DST) at the moment.

About Daylight Saving Time
Many locations in the world set their clocks from 2am (or 02:00) to 3am (or 03:00) in their local times when they begin daylight saving time. However, some places change their clocks at other times, depending on the daylight saving time rules.

Daylight Saving Time (or summertime as it is called in many countries) is a way of getting more light out of the day by advancing clocks by one hour during the summer. During Daylight Saving Time, the sun appears to rise one hour later in the morning, when people are usually asleep anyway, and sets one hour later in the evening, seeming to stretch the day longer.

The reason DST works is because its saves energy due to less artificial light needed during the evening hours—clocks are set one hour ahead during the spring, and one hour back to standard time in the autumn. Many countries observe DST, and many do not.

Note: Between March–April through September–November, it is summer in the northern hemisphere, where many countries may observe DST, while in the southern hemisphere it is winter. During the rest of the year the opposite is true: it is winter in the northern hemisphere and summer in the southern.

Benjamin Franklin first suggested Daylight Saving Time in 1784, but it was not until World War I, in 1916, when it was adopted by several counties in Europe that initially rejected the idea.

It is difficult to predict what will happen with Daylight Saving Time in the future. The daylight saving date in many countries may change from time to time due to special events or conditions.The United States, Canada and some other countries extended DST in 2007. The new start date is the second Sunday in March (previously the first Sunday in April) through to the first Sunday in November (previously the last Sunday in October).

DST transitions during 2010

These pages provide the times and dates for known DST transitions in 2010

In which direction does the clock move?

The clock moves ahead (thus, losing one hour) when DST starts, typically in the spring, and falls back one hour (thus, gaining one hour) when DST ends in the fall. To make it easier to remember which way the clock goes, keep in mind one of these sayings: “spring forward, fall back” or “spring ahead, fall behind.”

Is DST always one hour ahead of normal time?

Today it is almost always one hour ahead, but throughout history there have been several variants on this, such as half adjustment (30 minutes) or double adjustment (two hours), and adjustments of 20 and 40 minutes have also been used. A two-hour adjustment was used in several countries during the 1940s and elsewhere at times. A half adjustment was sometimes used in New Zealand in the first half of the 20th century. Sometimes DST is used for a longer period than just the summer, as it was in the United States during World War II. From February 3, 1942 to September 30, 1945 most of the United States had DST all year; it was called “War Time.”

How does the transition to DST start?

Click on a city in The World Clock and you can see information about that city, including if it practices daylight saving this year, and when it starts and when it ends. Let's say that DST starts at 2:00 am local time and DST is one hour:

DST start transition
Local timeDST or normal?Comments
1:59:58normal 
1:59:59normal 
3:00:00DSTDST started, time advanced by one hour
3:00:01DST 
3:00:02DST 

Note that local time between 2:00:00 — 2:59:59 does not exist during the transition from normal to DST. This hour is skipped, therefore this day has only 23 hours. Anyone who worked during the night from midnight to 8:00 a.m. has worked only seven hours because of the skipped hour.

How does the transition to DST end?

Let’ say that DST ends at 2:00 a.m. local time and DST is one hour ahead:

DST end transition
Local timeDST or normal?Comments
0:59:59DST 
1:00:00DST 
1:00:01DST 
time from 1:00:02 to 1:59:57 daylight saving time not shown
1:59.58DST 
1:59.59DST 
1:00:00normalTime is turned back to normal
1:00:01normal 
time from 1:00:02 to 1:59:57 normal time not shown
1:59.58normal 
1:59:59normal 
2:00:00normal 
2:00:01normal 

Note that local time from 1:00:00 to 1:59:59 is repeated this day. It first occurs during DST time, then clocks are turned back one hour to normal time and the time is repeated during normal time. To avoid confusion when referring to time within this hour, it is important to mention whether it was before or after the change back to normal time. The day when DST ends has 25 hours. Anyone who worked during the night from midnight to 8:00 a.m. has worked for nine hours because of the repeated hour.

More about Daylight Saving Time

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