On a hot summer day on the street to be clear, and we were exhausted from the heat, we often hear the phrase "the sun at its zenith."In our understanding, it is that a heavenly body is at the highest point and the most warm, one might even say, scorches the ground.Let's try a little dip in astronomy and to understand in more detail in this expression, and how right our understanding of this statement.
Earth parallels
from a school program, we know that on this planet there are so-called parallel, which are invisible (imaginary) line.Their existence is due to basic laws of geometry and physics, and the knowledge of where did these parallels are necessary in order to understand the whole course of geography.Accepted provide three most important line - the equator, the tropics and the Arctic Circle.
Equator Equator called invisible (notional) line that divides our planet into two identical hemispheres - South and North.It has long been known that the Earth is not based on three pillars, believed in ancient times, and has a spherical shape and, in addition to motion around the Sun rotates on its axis.It turns out that parallel the longest in the world, having a length of about 40 thous. 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, which is located between the tropics, gets the most solar heat and light.This is due to the fact that this region of the Earth is always turned toward the sun, so the rays are falling almost vertically.It follows that the equatorial areas on the planet has the highest temperature and the moisture-laden air masses create a strong evaporation.The sun at its zenith at the equator is twice a year, that is absolutely shines straight down.For example, in Russia it never occurs such a phenomenon.
Tropical
on the globe, there are southern and northern tropics.It is noteworthy that the sun is at its zenith here only once a year - on the day of the solstice.When a so-called winter solstice - 22 December turned to the sun as much as possible is the southern hemisphere, and on June 22 - on the contrary.
Sometimes tropical South and North are named after the constellations of the zodiac, which is the path of the sun these days.For example, South conventionally called the Tropic of Capricorn and the North - Cancer (December and June, respectively).
Arctic Circle Arctic Circle is considered to be a parallel, above which there is such a thing as the polar night or day.Location latitude, which are the polar circles, also has quite a mathematical explanation, it is minus 90 ° axial tilt of the planet.For the Earth, this value is equal to the Arctic Circle 66,5 °.Unfortunately, the inhabitants of temperate latitudes can not observe these phenomena.But the sun is at its zenith in the parallel corresponding to the Arctic Circle, the event is absolutely natural.
well-known fact
Earth is not standing still and, in addition to motion around the sun every day is rotated around its axis.During the year, we observe how the changing length of the day, the air temperature outside the window, and the most attentive will note change in the position of stars in the sky.For 364 days the Earth passes the full path around the sun.
Day and night
When we have a dark, ie the night, this suggests that the Sun in the time span covers the other hemisphere.There is quite a logical question why the day is equal to the duration of the night.The fact that the plane of the trajectory is not at a right angle relative to the Earth's axis.Indeed, in this case, we would not have seasons in which the ratio of the length of the day and night changes.
In the 20 days of March the sun leans toward the North Pole.Then, at about noon on the equator, you can exactly say that the sun is at its zenith.The following are the days when more northern points observed a similar phenomenon.On 22 June the sun is at its zenith on the Tropic of Cancer in the northern hemisphere this day is considered to be the middle of summer, and has a maximum longitude.For us, the most familiar is the definition - the phenomenon of the solstice.
interesting that after that day everything happens again, only in reverse order, and continues until the line of the equator in the afternoon the sun is at its zenith again - this happens on 23 September.At this time, the middle of summer begins in the southern hemisphere.
From all this it follows that when the sun is at its zenith at the equator, around the globe the duration of the night - 12 hours to the same length of time equal to the day.We used to call this phenomenon the day of the autumn or spring equinox.
Although the correct explanation of the concept of "the sun at its zenith," we discussed, it is still more common for us to be the wording that implies a simple finding of the sun as high as possible on a given day.
