How to understand the expression "the sun at the zenith"

On a hot summer day, when the weather is clear on the street and we are exhausted from the heat, we often hear the phrase "the sun at its zenith". In our understanding, we are talking about the fact that the heavenly body is at the highest point and warms as much as possible, one might even say that it scorches the earth. Let's try to plunge a bit into astronomy and understand more in this expression and in how true our understanding of this statement is.

Earth Parallels

Even with the school program, we know that on our planet there are so-called parallels, which are invisible (imaginary) lines. Their existence is conditioned by the elementary laws of geometry and physics, and knowledge of where these parallels came from is necessary in order to understand the whole course of geography. It is customary to distinguish three most important lines - the equator, the polar circle and the tropics.

Equator

The equator is called the invisible (conditional) line dividing our Earth into two identical hemispheres - the Southern and the Northern. It has long been known that the Earth is not on three whales, as believed in antiquity, but has a spherical shape and, in addition to the movement around the sun, rotates around its axis. So it turns out that the longest parallel on Earth, having a length of about 40 thousand km, is the equator. In principle, from a mathematical point of view, everything is clear, but does it matter for geography? And here, on closer examination, it turns out that the part of the planet that is located between the tropics gets the most sunlight and light. It is due to the fact that this area of the Earth is always turned towards the Sun, therefore the rays here fall almost vertically. It follows that on the equatorial parts of the planet the highest air temperature is observed, and the saturated air masses create a strong evaporation. The sun at the zenith at the equator is twice a year, that is, it shines absolutely vertically down. For example, in Russia there is never such a phenomenon.

Tropics

On the globe there are the Southern and Northern tropics. It is noteworthy that the sun at the zenith is here only once a year - on the day of the solstice. When the so-called winter solstice occurs on December 22, the Southern Hemisphere turns to the Sun as much as possible, and on the 22nd of June - on the contrary.

Sometimes the Southern and Northern tropics are named after the zodiacal constellation that is on the way of the Sun these days. So, for example, the Southern is conditionally called the tropic of Capricorn, and the North is called Cancer (December and June respectively).

Polar Circles

The polar circle is considered to be a parallel above which a phenomenon such as a polar night or day is observed. The location of the latitude on which the polar circles are located also has a completely mathematical explanation, it is 90 ° minus the inclination of the axis of the planet. For the Earth, this value of the polar circles is 66.5 °. Unfortunately, residents of temperate latitudes can not observe these phenomena. But the sun at the zenith on a parallel corresponding to the polar circle, the event is absolutely natural.

Well-known facts

The Earth does not stand still and, in addition to the movement around the Sun, rotates around its axis every 24 hours. During the year, we observe how the longitude of the day changes, the temperature of the air outside the window, and the most attentive can note the change in the position of the stars in the sky. For 364 days the Earth passes the full path around the Sun.

Day and night

When we are dark, that is, the night, this indicates that the Sun at a given period of time illuminates the other hemisphere. There is quite a logical question, why the day is not equal to the duration of the night. The fact is that the plane of the trajectory is not at a right angle with respect to the earth's axis. After all, in this case, we would not have the seasons in which the ratio of the longitude of the day and night changes.

In the 20-th of March, the North Pole leans toward the Sun. Then at about noon on the line of the equator you can absolutely say that the sun is at its zenith. Then there are days when a similar phenomenon is observed in more northern points. Already on June 22, the sun at the zenith is located on the tropic of Cancer, in the northern hemisphere this day is considered the middle of summer and has the maximum longitude. For us, the most common definition is the phenomenon of the solstice.

It is interesting that after this day everything happens anew, only in the reverse order, and continues until the sun is again at the zenith on the line of the equator at midday - this happens on September 23. At this time the middle of summer comes in the southern hemisphere.

From all this it follows that when the sun is at its zenith at the equator, the whole length of the night is 12 hours, the same length of time is equal to a day. We are accustomed to call this phenomenon the day of autumn or spring equinox.

Despite the fact that we correctly disassembled the correct explanation of the concept of "sun at the zenith", it is still more common for us to use the wording, which means simply finding the sun as high as possible on this particular day.