Daylight Saving Time (DST) happens in the summer and is also called ‘summer time’. Changing clock times back to ‘normal’ is called standard time, normal time, or ‘winter time’. DST clock changes take place early on Sunday mornings in the spring and fall of every year. It tends to creep up on people and those are the days when some church members are either an hour early or an hour late for church services.
Daylight Saving Time is actually very predictable. While the concept of “spring ahead and fall back” is taught in grammar school to help people remember the annual upcoming changes, the specific dates may vary each year. The start time, however, is consistent.
Daylight Saving Time always changes at 1 a.m. (01:00) on the coordinated universal time atomic 24-hour scale or UTC .
UTC relates to solar motion over a constant day of exactly 24 hours and is kept close to the mean solar time at the earth's prime meridian (zero degrees longitude) located near Greenwich, England. This is the time that is broadcast globally from the radio stations of the National Institute of Standards and Technology (NIST) and from GPS satellites ever since 1972 and is used for civil time-keeping purposes. This is, however, not exact with UT1, GMT - Greenwich Mean Time, or Zulu Time, which may vary from it by seconds or fractions of seconds, and are frequently used terms also. World time zones are expressed as positive or negative offsets from UTC.
When Daylight Saving Begins and Ends
In Canada and the United States, the annual days of changing to and from Daylight Saving Time are predictable, and are determined each year not by set dates, but by the month and by the day of the week. Starting 2007, DST was extended by one month and scheduled to begin an hour later.
DST normally began at 1 a.m. (01:00) UTC, and was usually on the last Sunday of March. In 2011, however, it began at 2 a.m. March 13, 2011, the second Sunday in March, an hour later and two weeks earlier than it began in 2010. It will be observed at 2 a.m. on Sunday March 11 in 2012 and will end on November 4, 2012.
DST normally ended at 1 a.m. (01:00) UTC on the first Sunday in November, and in 2011 also ended then (November 6, 2011) but an hour later at 2 a.m. In most other global locations using Daylight Saving Time, including England, DST ended in 2011 on Sunday October 30.
The actual time of day of the DST change for various cities varies globally, depending upon their time zone, and can be obtained by checking the World Clock for any given location.
Is Daylight Saving Time Global?
Daylight Saving Time is not mandated by law in America and some locations in the country do not comply with the time change. In most areas that do participate, local newscasters normally provide reminders during the regular evening news broadcasts of the upcoming time change.
While many people assume that all countries and territories in the world observe Daylight Saving Time, more locations do not observe it than those that do. While seventy-three locations routinely observe DST some or part of the year, more than one hundred fifty countries or territories do not observe it at all. Approximately another eighty or more countries have one or more locations within their borders that do observe it, while the rest do not.
Brazil, for instance, which normally has multiple time zones that appear to be imposed arbitrarily throughout the country and at many various times of the year, did not observing any Daylight Saving Time in 2010. This may have been to allow time to analyze and strategically standardize their country’s policies for DST in the future, but the reason was not announced. In the past, countries in the Southern hemisphere, in spite of having their seasons the exact opposite time of year as those in the Northern hemisphere, may have originally observed DST if it improved their trade or business operations with the United States, Canada, or the European Union.
The Effects on Health
Losing an hour of sleep each spring is usually a difficult transition for most people, even with the knowledge of gaining it back in the fall. The October 30, 2008 issue of the New England Journal of Medicine published an article entitled Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction on a study reporting that heart attack incidences increased significantly for the three week days after the DST transition in the spring.
Several studies done regarding the mental effects of either sleep deprivation or upsets in circadian rhythm that might be related to converting to DST, showed different results, possibly due to the global locations where the results were obtained. Data from an Australian study entitled Small shifts in diurnal rhythms are associated with an increase in suicide: The effect of daylight saving, used suicide data from 1971 to 2001 to determine what might be connected to a one-hour time shift due to DST. Australian male suicide rates rose immediately following the start of DST compared to the weeks immediately after returning to normal time. Results indicated that small changes in chronobiological rhythms are potentially destabilizing in vulnerable individuals.
The results of nationwide data from the Finnish Hospital Discharge Register providing information about hospital-treated accidents and manic episodes from two weeks before to two weeks after DST transitions during 1987–2003 were negative, and showed no significant effect on the incidence of related accidents or manic episodes that required hospital treatment.
References:
- Janszky I, Ljungand R. Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. N Engl J Med 10-30-2008; 359:1966-1968
- Daylight Saving Time Transitions and Hospital Treatments Due to Accidents or Manic Episodes
Marie Thomas - Marie Thomas (RieT) is an author in multiple genres, with 18 years in technical writing, and freelance work in science, biographical, and ...
