On a hot summer day, when the weather is clear and we are exhausted from high temperatures, we often hear the phrase "the sun is at its zenith." In our understanding, we are talking about the fact that the celestial body is located at the highest point and warms as much as possible, one might even say, scorches the earth. Let's try to plunge a little into astronomy and understand in more detail this expression and how true our understanding of this statement is.
Earth parallels
Ever since the school curriculum, we know that on our planet there are so-called parallels, which are invisible (imaginary) lines. Their existence is due to the elementary laws of geometry and physics, and knowledge of where these parallels come from is necessary in order to understand the entire course of geography. It is customary to single out the three most important lines - the equator, the Arctic Circle and the tropics.
Equator
EquatorIt is customary to call the invisible (conditional) line dividing our Earth into two identical hemispheres - the Southern and the Northern. It has long been known that the Earth does not stand on three whales, as was believed in ancient times, but has a spherical shape and, in addition to moving around the Sun, rotates around its axis. So it turns out that the longest parallel on Earth, which has a length of about 40 thousand km, is the equator. In principle, from a mathematical point of view, everything is clear here, but does this matter for geography? And here, upon closer examination, it turns out that the part of the planet that is located between the tropics receives the most solar heat and light. This is due to the fact that this region of the Earth is always turned towards the Sun, so the rays here fall almost vertically. It follows from this that the highest air temperature is observed in the equatorial regions of the planet, and air masses saturated with moisture create strong evaporation. The sun at its zenith at the equator happens twice a year, that is, it shines absolutely vertically down. For example, in Russia such a phenomenon never occurs.
Tropics
On the globe there are Southern and Northern tropics. It is noteworthy that the sun at its 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 June 22 - vice versa.
Sometimes the Southern and Northern tropics are named after the zodiac constellation that is on the path of the Sun in thesedays. So, for example, the South is conventionally called the Tropic of Capricorn, and the North - Cancer (December and June, respectively).
Arctic Circles
The Arctic Circle is considered to be a parallel, above which such a phenomenon as the polar night or day is observed. The location of the latitude at which the polar circles are located also has a completely mathematical explanation, this is 90 ° minus the tilt of the planet's axis. For the Earth, this value of the polar circles is 66.5 °. Unfortunately, inhabitants of temperate latitudes cannot observe these phenomena. But the sun at its zenith on the parallel corresponding to the polar circle, the event is absolutely natural.
Common Facts
The Earth does not stand still and, in addition to moving around the Sun, rotates around its axis every day. Throughout the year, we observe how the length of the day changes, the air temperature outside the window, and the most attentive can note the change in the position of the stars in the sky. In 364 days, the Earth travels a complete path around the Sun.
Day and night
When it's dark, that is, it's night, it means that the Sun in a given period of time illuminates the other hemisphere. A logical question arises why the day is not equal to the length of the night. The fact is that the plane of the trajectory is not at right angles to the earth's axis. Indeed, in this case, we would not have seasons in which the ratio of the longitude of day and night changes.
On the 20th of March, the North Pole leans towards the Sun. Then at about noon on the equator line, you can absolutelysay that the sun is at its zenith. This is followed by days when a similar phenomenon is observed at more northern points. Already on June 22, the sun at its zenith is located on the Tropic of Cancer, in the northern hemisphere this day is considered the middle of summer and has a maximum longitude. For us, the most familiar definition is the phenomenon of the solstice.
It is interesting that after this day everything happens anew, only in reverse order, and continues until the moment when the sun is at its zenith again on the equator line at noon - this happens on September 23rd. 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, on the entire globe the duration of the night is 12 hours, the same length of time is equal to the day. We used to call this phenomenon the day of the autumn or spring equinox.
Despite the fact that we have sorted out the correct explanation of the concept of "the sun at its zenith", the wording that simply means that the sun is as high as possible on this particular day will still be more familiar to us.
