Day by habit is divided into day, evening, night and morning. Or even just two periods: light - day, dark - night. Moreover, from the point of view of astronomy, few people think about what caused such a phenomenon.
And why does the sun shine so little in winter, making it feel like night falls at four or five in the afternoon.
Light and astronomical day: differences
The rotation of our planet around its so-called axis occurs in 24 hours. This is an astronomical day, which is divided into two parts: day and night. Half, that is, 12 hours, is an astronomical day. Its time and end is not fixed anywhere.
A day of light is a period of time that begins with sunrise and ends with its departure below the horizon. Therefore, the second name is a sunny day. The duration changes every day. And there is not a single day when the sun illuminates the earth for an equal amount of time. Just for a second, but it's different.
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By the way, often such information was printed on tear-off calendars that used to hang in every house. Confirmation of this fact is now easy to find on the Internet.
Day length factors
The tilt angle of the Earth to the Sun is 23.5 degrees, which is the main explanation for the short days in winter. In hot weather, the heavenly body lingers on the horizon for a long time, warming the surface. But in winter, everything happens exactly the opposite. The planet deviates from the star, so the sun's ray hits the earth indirectly and for a short time. And when it rains or is cloudy, it seems at all that the day ends before it starts.
By the way, beyond the Arctic Circle, the Sun passes along the horizon line, which entails darkness. This phenomenon is called polar night. On another conditional line - the equator - light and astronomical days are almost equal and their duration is about 12 hours.
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Considering that the Earth rotates on its axis at the same time as it rotates around the Sun, when winter sets in in the northern hemisphere, the day decreases. The division of the Earth from pole to pole, into the eastern and southern hemispheres, entails such a phenomenon as a change in time zones.
Winter solstice, or the shortest day
On December 21 or 22 of each year, the tilt of the earth's axis with respect to the Sun reaches its greatest angle. This astronomical phenomenon is called the solstice (solstice) and is characterized by the shortest, 8-hour day of the year. But from that moment on, night time gradually becomes shorter. In the southern hemisphere, the winter solstice is June 20 or 21.
Surely we all know that in winter the daylight hours become noticeably shorter. When we wake up in the morning to work or study, one can still watch the night outside the window, and when we return home in the evening, we also go either at dusk or in pitch darkness. But why the day becomes shorter in winter, not all people know, and today we will provide an accessible answer to this question.
global cause
If we talk briefly and globally about why the days are shorter in winter and the nights are longer, then the planetary scale features are to blame. It is about what trajectory and with what specific aspects the planet Earth rotates around its axis and around our natural luminary. And below we propose to understand this issue in more detail, so that you do not have any questions regarding this phenomenon.
In order to understand why the length of daylight hours on our planet changes in connection with the seasons, it is necessary to remember how the Earth rotates around the Sun, as well as the trajectory along which it moves around its own axis in relation to everything the same light of our universe.
The fact is that if you look at the imaginary axis of rotation of the planet, then in relation to the Sun and the trajectory of rotation around it, it is tilted. Accordingly, at whatever stage of the passage of the annual cycle of revolution around the Sun the Earth is, always some of its parts are located somewhat closer to the Sun, and some - further.
This, by the way, explains why at certain stages of the year winter is observed in some parts of the planet, and summer in others.
As for the main question, why the daylight hours are shorter in winter, it is necessary to pay attention to the fact that the trajectory of the Earth around its axis with respect to the Sun is such that in winter the northern hemisphere is more distant from the Sun. Such a trajectory, accordingly, affects the fact that most of the time of the rotation of the globe occurs without direct sunlight falling on it. And without the scattering of the light of the Sun, of course, there is no illumination on the surface of the Earth, that is, night is observed.
It is noteworthy that on our planet there are also such areas where the Sun does not rise for half a year, or does not fall below the horizon line, respectively - there is either a constant night or a constant day, which scientists call "Polar" day and night. Six months later, these sections change places, and the times of day there change in a similar way.
In order to easily understand why the sun rises early in summer, and winter nights are much longer than in summer, let's first imagine what exactly our planet Earth is and what the Sun is.
Rotation of the Earth around its axis
If you look at the sky at night, then many hundreds of stars are visible on it. It seems that some shine brighter, others not so much, but they and the Sun have one thing in common: the fact that the Sun is also an asterisk, only compared to others it is close to the Earth. And if you fly far into space, then it will seem the same star as all the others. Planet Earth is like a ball that spins around the stationary Sun, as if you take a ball and spin it around a light bulb. But if you just turn it, you will notice that the light bulb always illuminates only one side of the ball, as if it is always night on one side and day on the other. But this does not happen because the Earth also rotates around itself, like a spinning top or a ball on a basketball player's finger. If you mentally draw a line from your finger along the ball, then this will be the axis of rotation of the ball, and the Earth has such an imaginary axis.
Equator and hemispheres of the Earth
Drawing a line in the middle of the ball or the Earth so that two halves are obtained - the upper and lower - you get two hemispheres, on our planet they are called northern and southern, and the line separating them is the equator. The most important thing is that the axis of rotation of the Earth is not straight, but tilted, and that is why, when rotating around the Sun, the upper, northern, hemisphere in winter is still rejected from the Sun and warms less, and the southern one is larger, and when it is winter in Europe and Asia, then in South America and Australia it is summer. The upper and lower points of the exit of this axis from the surface of our planet are usually called the Pole, North and South.
The division of the day into astronomical and light
The word "day" has two meanings. There is such a definition as a solar, or light day, this is the period of time from sunrise to sunset at any point on the globe, and an astronomical, or calendar day, this is the time of half the rotation of the Earth around its axis. Together, night and day form an astronomical day, the rotation of the planet around its axis, and the Earth completes it in 24 hours. The length of daylight hours is always different, and during the year it can be from eight to sixteen hours, but it will be discussed later.
Winter and summer solstices
It is because of the tilt of the planetary axis, when our planet moves around the Sun, it seems that in winter it rises very late, and leaves the horizon too early. In autumn and winter, the northern hemisphere begins to receive less and less light from the Sun, the night becomes longer and the day shorter.
This continues until December 22, the day when the day is the shortest of the year, and the night is correspondingly long. This day is called the solstice, or the day of the winter solstice, and from that day the day gradually, literally by the minute, begins to increase. In summer there is also a similar day, June 22, the day of the summer solstice, when in summer this day is the longest, and the night is very short.
The length of the night and day at different points on the Earth is always different, and depends on how far this point is from the equator. This offset is called latitudinal offset, and in winter there are such latitudes when the sun does not appear at all because of the horizon for more than an astronomical day. This phenomenon is called the polar night, and the closer to the North Pole, the more it is. But after half a year, the opposite phenomenon occurs, when the sun is always on the horizon line, without descending at all, and the polar day sets in. Closer to the equator, the length of day and night is compared, and at the equator itself, the seasons do not replace each other, that is, neither winter nor summer, and the length of daylight hours is equal to night.
Instruction
Every day, as the Sun rises on the horizon from the east, it passes across the sky and disappears below the horizon in the west. In the northern hemisphere, this happens from left to right. People in the southern hemisphere see this move from right to left. A complete rotation of the Earth around its axis takes 24 hours. This rotation causes a change of day and night.
If 24 hours are divided equally, it turns out that 12 hours are day and 12 hours are night. At the equator, this is almost exactly what happens. But mid-latitude residents have noticed that this is not the case. In summer the day is long and in winter it is very short. Why then are the days so long in summer?
The thing is that the Earth's axis is tilted relative to the plane of its orbit. When the northern part of the axis is tilted towards the Sun, then it is summer in the northern hemisphere. The sun is high above the horizon at noon and needs more time to travel from east to west. Thus, a day lasts more than 12 hours (in the middle latitudes of both hemispheres, this is about 17 hours). But the days remain always of the same duration; therefore, the rest of the time (7 hours) remains at night.
But there is such an interesting fact: being in the middle of summer on, the Sun moves above the horizon around the clock. And then gradually its daily course inclines and the time comes when the Sun begins to hide behind the horizon line for a short time. And the closer to winter, the longer the sun does not appear. And in winter it is not in the sky at all. The polar night has come to the north pole. But how does it happen that the axis itself tilts either towards the Sun or away from it?
The axis does not deflect on its own, it is tilted constantly in one direction. It is the Earth that turns out to be on one side of the Sun, then on the other, passing around it in its orbit in 365 days. Thus, the north and south poles are alternately on the sunny side.
At the equator at noon, the Sun is slightly tilted to the horizon. In the middle of spring and in the middle of autumn, the Sun is at its zenith at noon, i.e. right over your head. At this time, upright objects do not cast a shadow. In mid-summer, the Sun is at its zenith above a latitude called the Tropic of Cancer. This is latitude 23°. In the middle of winter, on the contrary - the Sun is at its zenith at the same latitude above the southern tropic. It is called Capricorn (it is in this constellation that it is located at this time).
Thus, due to the tilt of the axis and the rotation of the Earth in orbit around its star, the seasons and the length of daylight hours change. There are also some deviations in the rotation of the Earth around its axis. The axis, as it were, itself rotates about its center (this is also the center of the globe). A full cycle of such rotation of the axis occurs in 25 thousand years and is called the Platonic year.
You probably noticed that it gets dark much later in summer than in winter. The day lasts longer, which means that you can walk, go about your business or stay awake for much longer.
But do you know why the days are shorter in winter and longer in summer? Today we will look into this issue.
Change of seasons
As part of the articles on our website, we have already considered information about why the seasons change on our planet in more detail, however, in order to understand why the days are longer in summer than in winter, it is necessary to recall the mechanics of how the principles of changing the seasons work.
The reason for the change in the seasons, and, accordingly, the weather, is primarily not the movement of the Earth around our natural luminary - the Sun, but around its own axis.
As we know, the Earth rotates around its own axis, but not all people know that our planet does not rotate around the Sun in a completely vertical position, since the conditional axis of rotation passes through the planet's ball at an angle.
It is due to such a trajectory of motion that our planet is in different positions relative to the Sun in winter and summer (in spring and autumn, respectively, also, but now this is not about that). And in such a situation, during the summer period, a specific area of the Earth's surface not only receives more sunlight, which creates a higher temperature, but the time of exposure to the Sun itself is longer. This leads to the fact that in summer the days are longer than in winter.
Longest day of the year
It is easy to guess why the longest day of the year is in summer, because in summer the daylight hours are always longer than in winter. Therefore, the longest day dates from the summer period. By the way, the longest day in the summer is observed on June 21, the summer solstice dates from this date.
Day length at the equator
As you know, our planet has an equator - located right in the central part of the globe. It is easy to guess that regardless of the trajectory of the Earth, at any time of the year and at any location relative to the Sun, the remoteness of the territories located on the equator will be the same. That is why here in summer the day is not longer than in winter, but exactly the same. As for the air temperature, here it is also not low, and occasionally drops below 24 degrees Celsius.
