What's the deal with the time change?
We often say that when it's not clear what it's all about, it's about money. Daylight saving time was first introduced in Germany in 1916, and it was done for economic reasons. In an effort to reduce electricity consumption, an hour of daylight was 鈥渢aken away鈥� from the afternoon to extend the morning鈥攁 time of day when people were more active at work
The primary reason for these changes is that the length of the day depends on the season. But why is that? How is this related to our geographical location?
Not everyone on Earth can watch the sunrise every day. For those living above the Arctic Circle, day or night may last longer than 24 hours.
The alternation of day and night is the result of the Earth鈥檚 rotation around its own axis and its orbit around a very powerful source of light 鈥� the Sun. Since the time of Copernicus, we have known that the Earth orbits the Sun in approximately 365.25 days. The Earth鈥檚 rotation period is less than 4 minutes shorter than a solar day (24 hours) 鈥� that is, the time between when we see the Sun directly overhead at noon. This motion can be compared to a spinning top attached by an invisible string to a lightbulb, around which it orbits. The Earth is like a tilted spinning top, in which the plane of the equator is tilted relative to the plane of the Earth鈥檚 orbit at an angle of 23.5掳 (this angle is called the obliquity of the ecliptic). As a result, during the first half of our orbital path (~183 days), the northern hemisphere receives more sunlight, and during the second half, the southern hemisphere does. And it is precisely this tilt that is the sole cause of the variation in the length of the day throughout the year depending on latitude. At the equator, the length of the day remains the same throughout the year, at just over 12 hours, while at the poles, the Sun remains above the horizon continuously for over half a year (polar day).
And what do we observe in Poland?
In the northernmost parts of the country, the shortest and longest days of the year last approximately 7 hours and 12 minutes and 17 hours and 20 minutes, respectively. Similarly, people living in the south experience day lengths ranging from approximately 8 hours and 10 minutes to 16 hours and 15 minutes. Although the difference in latitude between the north and south of our country is only ~5掳, this is sufficient for the summer solstice on ~21 June to be one hour longer on the Baltic coast than in the Tatra Mountains. Furthermore, seasonal temperature changes are caused not only by the length of time the Sun is above the horizon, but also by the angle at which the Sun鈥檚 rays strike the Earth. In Warsaw, the maximum angle of incidence of sunlight is only about 14.5掳 on the shortest day and about 61.5掳 on the longest. The greater this angle, the more solar energy falls on every square meter of soil surface, causing it to heat up. As a result, the conditions in which we live differ significantly depending on the season. We have also learned to convert solar radiation into electricity using new technologies (photovoltaic panels). If a 3-square-meter photovoltaic panel were 100% efficient, operating for just 2 hours a day would meet the electricity needs of a single average household.
So where did the idea for daylight saving time come from?
It鈥檚 important to note that, aside from differences in the length of the day, the sun rises at different times depending on longitude. In Poland, the day begins about 40 minutes earlier in the eastern parts of the country than in the western parts. That is why, for standard time 鈥� when the days get shorter and the sun rises later 鈥搘e set the clock hands back one hour. We do this in October, and on the last Saturday in March, we return to daylight saving time by changing the time on our clocks from 2:00 a.m. to 3:00 a.m.
By adjusting the time on clocks we will not change the length of the day or the climate, and therefore, from a physicist鈥檚 perspective, this change is unnecessary. The most important economic argument for daylight saving time, namely, the reduced need for artificial lighting, is now losing its validity. First, because LED lighting, which has since been invented and is now widely used, consumes about 10 times less energy than a traditional incandescent bulb. Second, the cost of generating electricity has decreased significantly. Additionally, there are issues related to changes in schedules and the extremely important impact of clock adjustments on people and animals. We should end the discussions about the need to move away from switching to daylight saving time and simply do it.
Let鈥檚 remember that whether it鈥檚 summer or winter, we should do everything we can to make it a happy time. Let鈥檚 be glad that our Earth has a tilt of 23.5掳, because thanks to that, we live in a colourful world where the seasons change and days vary in length. If this angle were 0掳, the idea of changing the time wouldn鈥檛 even occur to anyone and we鈥檇 have the same weather every day. And well, it would be boring and there鈥檇 be nothing to write about.
Source and edit: dr hab. Dorota Sobczy艅ska, Associate Professor at the 91桃色