Daylight hours: duration by months

The use and necessity of sunlight for the human body is not questioned. Any of us know that without it, existence is impossible. In winter, we all experience a more or less severe deficit, which adversely affects our well-being and undermines the already unstable immunity.

What happens with a light day

With the onset of the cold season, a light day, the duration of which is rapidly decreasing, is increasingly inferior to the law. The nights are longer and longer, and the days, on the contrary, are shorter. After the winter equinox period, the situation begins to change in the opposite direction, which most of us look forward to. A lot of people want to precisely orient themselves in the duration of the daylight hours at the present time and in the short term.

As you know, the number of light hours in the day begins to increase after the end of the so-called winter solstice. At its peak, a light day is recorded every year, the duration of which is the lowest. Scientifically, the explanation is to find the sun precisely at this time in the most remote point of the orbit of our planet. Influence on this has an elliptical (that is, elongated) form of the orbit.

In the northern hemisphere , the winter solstice day is in December and falls on the 21-22 number. A small offset of this date depends on the dynamics of the moon and the shifts in leap years. At the same time, the southern hemisphere is experiencing the reverse period of the summer solstice.

Daylight hours: duration, terms

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 light interval begins to increase gradually. And at first this process is practically not visible, since the addition takes only a few minutes a day. Later it starts to lighten faster, it is explained by an increase in the speed of solar rotation.

In fact, the increase in the duration of daylight hours in the northern hemisphere of the Earth does not begin 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. The increase in daylight intensity has an appreciable positive effect on the health of people.

According to astronomers, the winter solstice is the time when the sun reaches the lowest angular height above the horizon. After it for several days, the sun can start its sunrise even a little later (for a few minutes). The increase in the duration of the light day is observed in the evenings and takes place at the expense of an increasingly late sunset.

Why is it so

This effect is also due to an increase in the speed of the Earth's motion. You can verify this by looking at the table, which reflects the sunrises and sunsets. As astronomers say, the day is added in the evening, but unevenly from both sides. The plot of the duration of the daylight gives a clear picture of the dynamics of this process.

Every day the sun sets for a few minutes. Accurate data can be easily traced to the appropriate tables and calendars. As explained by scientists, this effect is caused by a combination of daily and annual sun movements across the sky, which in winter is slightly faster than in summer. In turn, this is due to the fact that, when rotating at a constant speed around its own axis, the Earth in winter is located closer to the Sun and moves orbit around it slightly faster.

The elliptical orbit along which our planet moves has a pronounced eccentricity. This term indicates the elongation elongation. The point of this eccentricity closest to the Sun is called the perihelion, and the most distant point is the aphelion.

Kepler's laws state that for a body moving along an ellipse in the shape of an ellipse, the maximum velocity is characteristic at those points that are as close to the center as possible. That is why the movement of the sun on the sky in the winter is slightly more rapid than in the summer.

How the Earth's orbital motion affects the climate

As the astronomers consider, the point of peregeliya the Earth passes approximately on January, 3rd, and aphelion - on July, 3rd. Possible changes in these dates for 1-2 days, which is due to the additional influence of the movement of the moon.

The ellipsoid 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 slightly less noticeable the difference between the climatic seasons of our northern hemisphere.

At the same time, this difference is more noticeable in the Southern Hemisphere. As established by scientists, one turn of the point of peregelia occurs over about 200,000 years. That is, after about 100 000 years the situation will change to the exact opposite. Well, we'll see if we live!

Give us the sunshine!

If we go back to the current problems, then most important for us is the fact that the emotional, mental and physical state of the inhabitants of the Earth improves in direct proportion to the increase in the duration of daylight hours. Even an insignificant (for a few minutes) elongation 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 due to the increase in the production of the hormone serotonin, which controls the emotions of happiness and joy. Unfortunately, in the dark it is produced extremely badly. That is why increasing the duration of the light gap by affecting the emotional sphere leads to a general 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 tied to the alternation of day and night that continues from the moment of the creation of the world. Scientists are sure that we can adequately work and cope with external overloads, our nervous system can only regularly receive a definite dose of sunlight.

When light is not enough

If the sunlight is not enough, the consequences can be the most sad: from regular nervous breakdowns to serious mental disorders. With an acute lack of light, a depressive state can develop. A seasonal affective disorders, which are expressed in depression, bad mood, a general decline in the emotional background is observed very often.

In addition, modern citizens are prone to another scourge. A light day, the duration of which is too short for modern urban life, requires adjustments. This is a huge, often unnecessary amount of artificial lighting, which is received by almost any inhabitant of the metropolis. Our body, unadapted to such an amount of artificial light, is able to get lost in time and fall into the state of desynchronosis. This leads not only to the weakening of the nervous system, but also to 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, actual for each of us in the first days after the winter solstice. This term denotes the time interval that lasts from sunrise to sunset, that is, the time during which our star is visible above the horizon.

This value is in direct proportion to the solar declination and geographical latitude of the point where it needs to be determined. In the equator area, the magnitude of the longitude 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

Days when the duration of the night coincides with the duration of the day, called the days of the vernal equinox, or autumn. This occurs on March 21 and September 23, respectively. It is clear that the highest figure reaches the longitude of the day at the time of the summer solstice, and the lowest - on the winter day.

Behind the polar circles of each hemisphere, the magnitude of the longitude of the day rises over 24 hours. It is a question of the well-known concept of the polar day. At the poles, it has a duration of six months.

The longitude of the day at any point in the hemisphere can be determined quite accurately by means of special tables containing the calculation of the duration of the light day. Of course, this figure changes daily. Sometimes for a rough estimate uses such a concept as the average duration of a light day by months. For clarity, consider these figures for the geographical point where the capital of our country is located.

The length of a day in Moscow

In January, the light day at the latitude of our capital is an average of 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 see that the June days are the longest, which corresponds to the summer solstice.

In autumn the light day continues to decline. In September and October, its duration is 12 hours 45 minutes and 10 hours 27 minutes respectively. Record short bright days are famous for the last cold dark months of the year - November and December, the average duration of which does not exceed 8 hours 22 minutes and 7 hours 16 minutes respectively.