The benefits and necessity of sunlight for the human body is beyond doubt. Any of us knows that without it existence is impossible. In winter, we all experience a more or less severe deficiency of it, which negatively affects our well-being and undermines our already fragile immunity.
What happens to daylight hours
With the onset of the cold season, daylight hours, the duration of which is rapidly decreasing, are increasingly giving way to rights. The nights are getting longer and longer, and the days, on the contrary, are getting shorter. After the winter equinox period, the situation begins to change in the opposite direction, which most of us look forward to. Many people want to accurately navigate the length of daylight hours now and in the near future.
As you know, the number of light hours per day begins to increase after 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 shortest. From scientificpoint of view, the explanation is that the sun is at this time at the most distant point in the orbit of our planet. This is influenced by the elliptical (that is, elongated) shape of the orbit.
In the northern hemisphere, the winter solstice occurs in December and falls on the 21st-22nd. A slight shift in this date depends on the dynamics of the Moon and shifts in leap years. At the same time, the southern hemisphere experiences the reverse of the summer solstice.
Light day: 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 end of the darkest day, the light gap begins to gradually increase. Moreover, at first this process is practically invisible, since the addition occurs only for a few minutes a day. In the future, it begins to brighten faster, this is explained by an increase in the speed of solar rotation.
In fact, the increase in the length 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 20 to 22 June. The increase in daylight hours has a noticeable positive effect on people's he alth.
According to astronomers, the winter solstice is the moment when the sun reaches its lowest angular height above the horizon. After it, for several days, the sun can begin its sunrise even a little later (for several minutes). Growththe duration of daylight is observed in the evenings and is made due to the increasingly late sunset.
Why does this happen
This effect is also explained by the increase in the speed of the Earth. You can verify this by looking at the table, which reflects the sunrise and sunset. As astronomers say, the day is added in the evening, but unevenly on both sides. The daylight graph gives a visual representation of the dynamics of this process.
The sunset shifts by a few minutes every day. Accurate data is easy to follow on the relevant 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 a little 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 elliptical orbit along which our planet moves has a pronounced eccentricity. This term refers to the amount of elongation of the ellipse. The point of this eccentricity closest to the Sun is called perihelion, and the most distant one is called aphelion.
Kepler's laws state that a body moving in an elliptical orbit is characterized by maximum speed at those points that are as close as possible to the center. That is why the movement of the sun across the sky in winter is slightly faster than in summer.
How the Earth's orbital movement affects climate
As they thinkastronomers, the Earth passes the point of perhelion approximately on January 3, and aphelion - on July 3. These dates may change by 1-2 days, which is due to the additional influence of the movement of the Moon.
The elliptical shape of the Earth's orbit also affects the climate. During the winter in the Northern Hemisphere, our planet is closer to the Sun, while in the summer it is further away. This factor makes the difference between the climatic seasons of our northern hemisphere a little less noticeable.
At the same time, this difference is more noticeable in the Southern Hemisphere. As established by scientists, one revolution of the overhelion point occurs in about 200,000 years. That is, in about 100,000 years, the situation will change to the exact opposite. Well, we'll live and see!
Give me sunshine
If we return to current problems, the most important thing for us is the fact that the emotional, mental and physical state of the inhabitants of the Earth is improving in direct proportion to the increase in the length of daylight hours. Even a slight (for a few minutes) lengthening of the day immediately after the winter solstice has a serious moral effect on people tired of the dark winter evenings.
From a medical point of view, the positive effect of sunlight on the body is due to an increase in the production of the hormone serotonin, which controls 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 interval by influencing the emotional sphere leads to a general improvement in well-being and strengthening of humanimmunity.
A significant role in the sensations of each of us is played by daily internal biorhythms, which are energetically tied to the alternation of day and night that has continued since the creation of the world. Scientists are sure that our nervous system can adequately work and cope with external overloads only by regularly receiving a very certain dose of sunlight.
When there is not enough light
If the sun's rays are not enough, the consequences can be the saddest: from regular nervous breakdowns to serious mental disorders. With an acute lack of light, a real depressive state can develop. And seasonal affective disorders, which are expressed in depression, bad mood, a general decrease in the emotional background, are observed all the time.
In addition, modern citizens are subject to another misfortune. Daylight hours, the duration of which is too short for modern urban life, require adjustment. We are talking about a huge, often excessive amount of artificial lighting, which is received by almost any resident of the metropolis. Our body, unadapted 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 the exacerbation of any existing chronic diseases.
What is the length of the day
Let's now consider the concept of the length of the day, which is relevant for each of us in the first days after the winter solstice. This term refers to the interv althe time that lasts from sunrise to sunset, that is, the time during which our luminary is visible above the horizon.
This value is directly dependent on the solar declination and the geographical latitude of the point where it needs to be determined. At the equator, the length of the day does not change and is exactly 12 hours. This figure is 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 spring equinox, or autumn. This happens on March 21 and September 23 respectively. It is clear that the longitude of the day reaches its highest figure at the time of the summer solstice, and the lowest - on the winter day.
Beyond the polar circles of each of the hemispheres, the longitude of the day exceeds the limit in 24 hours. We are talking about the well-known concept of the polar day. At the poles, it lasts as long as half a year.
The length of the day at any point in the hemisphere can be determined quite accurately using special tables containing the calculation of the length of daylight hours. Of course, this number changes daily. Sometimes, for a rough estimate, he uses such a concept as the average length of daylight hours by month. For clarity, consider these figures for the geographical point where the capital of our country is located.
Length of daylight hours in Moscow
In January daylight hours at the latitude of our capital isaverage 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 figures are 17 hours 19 minutes, 16 hours 47 minutes and 14 hours 59 minutes. We can see that June days are the longest, which corresponds to the summer solstice.
In autumn, daylight hours continue to shrink. 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 famous for their record short bright days, the average day length of which does not exceed 8 hours 22 minutes and 7 hours 16 minutes, respectively.
