The benefits and necessity of sunlight for the human body is not in doubt. Each of us knows that without it, existence is impossible. In winter, we all experience a more or less severe deficit, which negatively affects our well-being and undermines the already unstable immunity.
What happens to daylight
With the onset of the cold season, daylight hours, the duration of which is rapidly decreasing, are increasingly losing ground. Nights are made longer and longer, and days, on the contrary, are shorter. After the period of the winter equinox, the situation begins to change in the opposite direction, which most of us look forward to. Many people want to accurately navigate the duration of daylight hours now and in the near future.
As you know, the number of light hours per day begins to increase at the end of the period of the so-called winter solstice. At its peak, daylight hours are recorded annually, the duration of which is the lowest. From a scientific point of view, the explanation is the finding of the sun at this time at the most distant point in the orbit of our planet. This is influenced by the elliptical (i.e. elongated) shape of the orbit.
In the northern hemisphere , the winter solstice occurs in December and falls on the 21-22th day. A small shift in this date depends on the dynamics of the moon and shifts in leap years. At the same time, the southern hemisphere is experiencing the reverse period of summer solstice.
Daylight hours: duration, timing
A few days before and after the date of each solstice, the daylight does not change its position. Only two or three days after the completion of the darkest days, the luminous gap begins to gradually increase. Moreover, at the beginning this process is practically not visible, since the addition takes place only for a few minutes a day. In the future, it begins to brighten faster, this is due to an increase in the speed of solar rotation.
In fact, an increase in the duration of daylight hours in the northern hemisphere of the Earth begins no earlier than December 24-25, and it occurs until the very date of the summer solstice. This day alternately falls on one of three: from June 20 to June 22. An increase in daylight has a noticeable positive effect on people's health.
According to astronomers, the winter solstice is considered the moment the sun reaches the lowest angular height above the horizon. After it, for several days the sun can begin to rise even a little later (for several minutes). An increase in the duration of daylight hours is observed in the evenings and is due to an ever-later sunset.
Why it happens
This effect is also due to an increase in the speed of the Earth. You can verify this by looking at the table where the sunrises and sunsets are reflected. According to astronomers, the day is added in the evening, but unevenly on both sides. A graph of daylight hours gives a visual representation of the dynamics of this process.
Daily sunset shifts for several minutes. Accurate data can be easily traced to the corresponding tables and calendars. As scientists explain, this effect is caused by a combination of daily and annual movements of the sun across the sky, which is slightly faster in winter than in summer. In turn, this is due to the fact that, turning at a constant speed around its own axis, the Earth in winter is located closer to the Sun and moves in orbit around it a little faster.
The ellipsoidal orbit on which our planet moves has a pronounced eccentricity. This term refers to the elongation of an ellipse. The point of this eccentricity closest to the Sun is called perihelion, and the most distant - aphelion.
Kepler's laws state that a body moving in an orbit in the form of an ellipse is characterized by a maximum speed at those points that are as close to the center as possible. That is why the movement of the sun in the sky in winter is slightly faster than in summer.
How does Earth's orbit affect climate
According to astronomers, the Earth transfusion point passes around January 3, and aphelion - July 3. Possible changes in these dates for 1-2 days, due to the additional influence of the movement of the moon.
The ellipse-like shape of the Earth’s orbit also affects the climate. During the winter in the Northern Hemisphere, our planet is located closer to the Sun, in the summer - further. This factor makes the difference between the climatic seasons of our northern hemisphere a little less noticeable.
At the same time, in the Southern Hemisphere this difference is more noticeable. As established by scientists, one revolution of the crossover point occurs in about 200,000 years. That is, after about 100,000 years, the situation will change to the exact opposite. Well, if we survive, we will see!
Give the sunshine!
If we return to the current problems, the most important thing for us is the fact that the emotional, mental and physical condition of the inhabitants of the Earth improves in direct proportion to the increase in the duration of daylight hours. Even a slight (for several minutes) lengthening of the day immediately after the winter solstice has a serious moral effect on people tired of dark winter evenings.
From a medical point of view, the positive effect of sunlight on the body is explained by an increase in the production of the hormone serotonin, which manages the emotions of happiness and joy. Unfortunately, in the dark it is produced extremely poorly. That is why an increase in the duration of the light gap by affecting the emotional sphere leads to an overall improvement in well-being and strengthening of human immunity.
A significant role in the sensations of each of us is played by daily internal biorhythms, which are energetically attached to the alternation of day and night, which has continued since the creation of the world. Scientists are confident that our nervous system can only adequately work and cope with external overloads by regularly receiving a certain dose of sunlight.
When there is not enough light
If the sun's rays are not enough, the consequences can be most sad: from regular nervous breakdowns to serious mental disorders. With an acute lack of light, a real depressive state can develop. And seasonal disorders of an affective nature, which are expressed in depression, poor mood, a general decrease in the emotional background, are observed quite often.
In addition, modern citizens are prone to another misfortune. Daylight hours, the duration of which is too short for modern urban life, require adjustment. This is a huge, often excessive amount of artificial lighting, which is received by almost any resident of the metropolis. Our body, not adapted to such an amount of artificial light, is able to get confused in time and fall into a state of desynchronosis. This leads not only to a weakening of the nervous system, but also to an exacerbation of any existing chronic diseases.
What is the longitude of the day
Let us now consider the concept of the longitude of the day, relevant for each of us in the first days after the winter solstice. This term refers to the period of time that lasts from sunrise to sunset, that is, the time during which our star is visible above the horizon.
This value is directly dependent on solar declination and the geographical latitude of the point where it needs to be determined. At the equator, the longitude of the day does not change and is exactly 12 hours. This figure is a borderline. For the northern hemisphere, in spring and summer, the day lasts longer than 12 hours, in winter and autumn - less.
Autumn and spring equinox
The days when the length of the night coincides with the length of the day are called the days of the vernal equinox, or autumn. This happens on March 21 and September 23, respectively. It is clear that the longest day reaches the highest figure at the time of the summer solstice, and the lowest - on a winter day.
Beyond the polar circles of each hemisphere, the magnitude of the longitude of the day rolls over 24 hours. We are talking about the well-known concept of a polar day. At the poles, it has a duration of as much as six months.
The longitude of the day at any point in the hemisphere can be determined quite accurately from special tables containing the calculation of the duration of daylight hours. Of course, this figure changes daily. Sometimes, for a rough estimate, it uses a concept such as the average daylight hours for months. For clarity, we consider these figures for the geographical point where the capital of our country is located.
Daylight hours in Moscow
In January, daylight hours at the latitude of our capital is on average 7 hours 51 minutes. In February - 9 hours 38 minutes. In March, its duration reaches 11 hours 51 minutes, in April - 14 hours 11 minutes, in May - 16 hours 14 minutes.
During the three summer months: June, July and August - these numbers are 17 hours 19 minutes, 16 hours 47 minutes and 14 hours 59 minutes. We see that the June days are the longest, which corresponds to the summer solstice.
Autumn daylight continues to decline. In September and October, its duration is 12 hours 45 minutes and 10 hours 27 minutes, respectively. The last cold dark months of the year, November and December, are known for record short bright days, the average day length of which does not exceed 8 hours 22 minutes and 7 hours 16 minutes, respectively.