Life on our planet depends on the amount of sunlight and heat. It is terrible to imagine, even for a moment, what would have happened if there had not been such a star in the sky as the Sun. Every blade of grass, every leaf, every flower needs warmth and light, like people in the air.
The angle of incidence of the sun's rays is equal to the height of the sun above the horizon
The amount of sunlight and heat that enters the earth's surface is directly proportional to the angle of incidence of the rays. The sun's rays can fall on the Earth at an angle from 0 to 90 degrees. The angle of the rays hitting the earth is different, because our planet has the shape of a ball. The larger it is, the lighter and warmer it is.
Thus, if the beam comes at an angle of 0 degrees, it only slides along the surface of the earth, without heating it. This angle of incidence occurs at the North and South Poles, beyond the Arctic Circle. At right angles, the sun's rays fall on the equator and on the surface between the Southern and Northern Tropics.
If the angle of the sun's rays on the ground is straight, it means that the sun is at its zenith.
So the angle of incidencerays on the surface of the earth and the height of the sun above the horizon are equal to each other. They depend on geographic latitude. The closer to zero latitude, the closer the angle of incidence of the rays is closer to 90 degrees, the higher the sun is above the horizon, the warmer and brighter.
How the sun changes its height above the horizon
The height of the sun above the horizon is not a constant value. On the contrary, it is always changing. The reason for this lies in the continuous movement of the planet Earth around the star Sun, as well as the rotation of the planet Earth around its own axis. As a result, the day follows the night, and the seasons change each other.
The area between the tropics receives the most heat and light, here the day and night are almost equal in duration, and the sun is at its zenith 2 times a year.
The surface beyond the Arctic Circle receives less and less heat and light, there are such concepts as polar day and night, which last about six months.
Days of the autumn and spring equinoxes
The 4 main astrological dates are highlighted, which determine the height of the sun above the horizon. September 23 and March 21 are the autumn and spring equinoxes. This means that the height of the sun above the horizon in September and March these days is 90 degrees.
The southern and northern hemispheres are equally illuminated by the sun, and the longitude of the night is equal to the longitude of the day. When astrological autumn comes in the Northern Hemisphere, then in the Southern Hemisphere, on the contrary, spring. The same can be said about winter and summer. If it is winter in the Southern Hemisphere, then it is summer in the Northern Hemisphere.
Days of summer and winter solstices
June 22 and December 22 are the summer and winter solstices. December 22 sees the shortest day and longest night in the Northern Hemisphere, and the winter sun is at its lowest altitude all year.
Above latitude 66.5 degrees the sun is below the horizon and does not rise. This phenomenon, when the winter sun does not rise to the horizon, is called the polar night. The shortest night is at a latitude of 67 degrees and lasts only 2 days, and the longest night is at the poles and lasts 6 months!
December is the month of the year with the longest nights in the Northern Hemisphere. People in Central Russia wake up to work in the dark and return at night too. This is a difficult month for many, as the lack of sunlight takes a toll on the physical and moral condition of the people. For this reason, depression may even develop.
In Moscow in 2016, the sunrise on December 1 will be at 08.33. In this case, the length of the day will be 7 hours 29 minutes. Sunset over the horizon will be very early, at 16.03. The night will be 16 hours 31 minutes. Thus, it turns out that the longitude of the night is 2 times longer than the longitude of the day!
This year's winter solstice is December 21st. The shortest day will last exactly 7 hours. Then the same situation will last for 2 days. And already from December 24, the day will turn into profit slowly but surely.
On average per day will beadd one minute of daylight. At the end of the month, the sunrise in December will be at exactly 9 am, which is 27 minutes later than December 1st
June 22 is the summer solstice. Everything happens exactly the opposite. For the whole year, it is on this date that the longest day in duration and the shortest night. This is about the Northern Hemisphere.
In the South it's the opposite. Interesting natural phenomena are associated with this day. Beyond the Arctic Circle comes the polar day, the sun does not set below the horizon at the North Pole for 6 months. Mysterious white nights begin in St. Petersburg in June. They last from about mid-June for two to three weeks.
All these 4 astrological dates may vary by 1-2 days, as the solar year does not always coincide with the calendar year. Also offsets occur in leap years.
Height of the sun above the horizon and climatic conditions
The sun is one of the most important climate-forming factors. Depending on how the height of the sun above the horizon over a particular area of the earth's surface has changed, climatic conditions and seasons change.
For example, in the Far North, the rays of the sun fall at a very small angle and only glide along the surface of the earth without heating it at all. Under the condition of this factor, the climate here is extremely harsh, there is permafrost, cold winters with freezing winds and snows.
The higher the sun above the horizon, the warmer the climate. For example, at the equatorextremely hot, tropical. Seasonal fluctuations are also practically not felt in the equator region, in these areas there is eternal summer.
Measuring the height of the sun above the horizon
As they say, everything ingenious is simple. So here. The device for measuring the height of the sun above the horizon is elementary simple. It is a horizontal surface with a pole in the middle 1 meter long. On a sunny day at noon, the pole casts the shortest shadow. With the help of this shortest shadow, calculations and measurements are carried out. It is necessary to measure the angle between the end of the shadow and the segment connecting the end of the pole to the end of the shadow. This value of the angle will be the angle of the sun above the horizon. This device is called a gnomon.
Gnomon is an ancient astrological instrument. There are other devices for measuring the height of the sun above the horizon, such as sextant, quadrant, astrolabe.
