What is summer time, different from winter time?

Summer Time - also known as DST (Daylight Saving Time) is a type of convention that adjusts the time according to the actual time period in the daylight. For countries adopting this convention, at the time between mid-spring (late March) and early winter (late October and early November), the clock will be adjusted faster than 1 hour. The remaining time, the clock will be adjusted to the same.

Why do you need to adjust the clock?

When talking about time, people often understand two concepts. The first concept is the time based on the brightness of the day. With this understanding, it is possible to divide the day into two parts, " daytime", ie the time of morning, and "night" . The second way to indicate time is to divide the day into equal intervals, as most people now understand a day is divided into 24 hours.

However, due to the physical nature (the axis of the Earth deviates from a 23.5 degree angle), between different seasons the time of light in each day is also different. In summer, the daytime will be longer than the nighttime, while in the winter it is the opposite. This phenomenon is more evident in places near the poles of the earth.

In the summer, the sun rises earlier, and the day is longer.(Photo: National Geographic)

People from ancient times have recognized this phenomenon. Some societies, such as the ancient Romans, divide the time of day by equalization of daytime intervals, and these times may vary by season. For example, with their water meter, at the time of winter solstice (in the middle of winter), each day lasts only 44 minutes at present, while in the summer solstice (mid-summer), each hour of pulling up to 75 minutes long.

By summer time convention, the watch will be adjusted up to an hour early in most of the year.(Photo: iStockPhoto)

In the future, the way to divide a day into 24 hours began to be popular and widely used. The characteristic of this division is that the actual time of each hour is constant between different times of the year. However, this division will make the use of daylight less effective.

In society, working or studying time is often strictly regulated, according to the convention of 24 hours per day. Meanwhile, the body's activity often follows the control of light: Wake up and be healthy when it is morning, and go to sleep when it's dark. Therefore, if applying the winter working time in the summer, people will only wake up when the sun has been shining for several hours, reducing work efficiency.

The fact that people sleep later in the summer will also make electricity more used to light, causing energy waste. This is of more interest from the second half of the last century, when energy shortage became a problem for many countries. That's why the summer time convention is recommended, and is also known as the "Daylight Saving Time" (DST).

When is the clock adjustment time?

Conventional summer time is usually applied from the end of March to the end of October, which is more than half a year. However, the regulation of each country is different, and not every country applies this convention.

Map of areas currently applied DST (blue) and not (red and orange).(Photos: Wikipedia)

In Asia, only some countries that apply DST such as Iran, Israel, Turkey . Vietnam and large countries such as China, Japan or South Korea do not apply this convention. Countries applying DST usually start from the last Friday of March, to the Friday or the last Sunday of October.

In Europe, most countries except Russia, Iceland and Belarus apply the summer time convention. The time of application of DST is calculated from 1 am (GMT) on the last Sunday of March, and ends at 1 am on the last Sunday of October.

In the Americas, three countries in North and Central America (Canada, USA and Mexico) and some countries in South America apply DST. In the United States, some states do not apply this convention. In most other states, the clock is adjusted at 2 am on the second Sunday of March, and revised on the first Sunday of November.

What effect does the clock adjustment have?

Only through a few examples above, we can see that the time to adjust the clock according to DST in the world is very diverse and complicated. The application of this convention also has a lot of impact on human health, requires adjustment process and is also controversial about the application.

Many studies show that adjusting clocks early in the end of March has affected human health . Specifically, adjusting the time will affect sleep, and it may take several days to get used to again. A study in 2008 also found that, in the first week after adjusting the time, the number of heart attacks will increase dramatically.

Does DST really save energy?(Photo: ABC News)

Another goal of DST is that energy savings are not really convincing. Although people will sleep earlier in the summer, they still go to work every day, so they still need energy to turn on the lights during working time. In addition, longer days also make people spend more time outside, so gasoline or electricity to run a car will be more expensive.

At the time of summer time, people need to adjust activities that match the new hours

Modern computers and phones all have the DST auto-adjust feature, but this feature is not always active. Besides the recent bug of iOS 7, Apple also had problems with DST in 2010, when the error on iOS 4 caused the alarm clock to be delayed an hour after the time was adjusted. The change of time also makes time-related jobs such as performances, flight hours . changed, reversed and brought about many misunderstandings.

In Vietnam, while not applying Summer time, you can still realize its impact if you follow international events, or work with foreigners. In particular, if you are a football fan, you will easily see DST's influence.

For most of the season, football fans will have to stay up late to watch exciting matches

UEFA Champions League matches usually take place at the same time, at 7:45 PM GMT. At the beginning of the season, because Europe adjusted the time and Vietnam did not, these first matches took place at 1:45 am Vietnamese time.

However, since November until the end of March, most of the time of a football season, time is revised, and UEFA Champions League matches take place at 2:45 am, and will end quite late (near 5 am), affecting the schedule of activities and work of Vietnamese people.