time, as you know - a relative term, and in some cases, and extensible.We are used to divide it into years, months, days, hours, minutes and seconds.But such a term as the afternoon - this is how long?It turns out that the answer to this question is not as easy as it seems at first glance.And if you say that afternoon - it is noon, you can make a mistake.Does this mean that the term as relyativen, like all human vremyaischislenie?Yes and no.Let's try to examine this issue more deeply.
Day
To answer the question, "Noon - is how long?", You need to know the measure of what it is.This constant is the astronomical definition for the middle of the day.And how do they differ from the date or day?In the English language, which, as we know, is more functional than the Russian, this is no analogue in the dictionary.The average man in the street says the day, which means "day".A rigorous notation days as such consume more accurate term - 24 hours.It is also common phrase day and night.In Slavic languages the word "day" or "Doba" comes from the word "meeting" and "joint".Thus, the new day begins at sunset, or after-burning, or at dawn, that is, when there are dark and daylight.Noon, as is clear from the etymology of the word, is the middle of the day.
solar and sidereal day
We used to think that the time unit is made up of twenty-four hours, but astronomers distinguish between solar and sidereal day, which are not equal to each other.Our planet rotates around its axis 24 hours, but due to the orbital motion of the Earth's sun moves, so the sidereal day lasts twenty-three hours and fifty-six minutes and four seconds.There is something to ponder!Moreover, as the Earth moves around the sun unevenly.To correct the error, regularly December 31 or June 30 introduced the so-called "leap second."To determine this afternoon - is how long - at the observatory in Greenwich date of the vernal or autumnal equinox.The upper edge of the solar disk should climb above the ground at 6 am and disappear from sight at 6pm.And in the middle of the afternoon the light is at the highest point in the sky - at its zenith.
Day and night
In everyday life we often substitute these two concepts.So, we say "the day of June 18," implying that entire period of time ranging from 0 to 23 hours, 59 minutes and 59 seconds.But not always the boundaries of the day served at midnight.The ancient Greeks, Egyptians and Slavic counted from the beginning of a new day dawn.In the Jewish tradition, "Yamama", ie day begins when the sky light up the first star (ie after sunset).Vestige of such calculation time was in the "Eves" in the celebration of major religious holidays, so it was difficult to compare two values.Noon - is how long?It could be like six hours and seventeen.Especially in the temperate latitudes of the daylight hours it depends on the season.And how then to determine the afternoon in the Arctic Circle, where our star may not appear for days?
constant and relative
It would seem that everything is simple.The sun at noon is at its zenith, ie, it reaches a maximum height in the sky.Light in our latitudes rises are not exactly in the east and slightly south, and moving it on the edge of the noonday sky.Thus, when it reaches the maximum height and starts its movement to set, the location can be defined as strictly southern.At the equator the afternoon - this is where the light shines evenly over the head.And in the southern hemisphere at this time the sun is visible even in the north.Time of day - the day, morning, evening and night - varies depending on the season.In the summer it gets dark later, somewhere there are white nights and early winter night descends.But the afternoon - it is constant.At this time, the shadows are the shortest (in the tropics, they are generally hidden under the feet), so easy to calculate the afternoon.Go on a flat area, broke into a vertical ground peg.Next set the compass.When the shadow of the peg will point exactly to the south, then came noon.
What prevents to determine the exact time
It's all theory.And what will happen if we do decide on this simple experiment?For example, we hold our experience in Berdyansk (Ukraine).The experimental result shows that there occurs at 11 noon hours and 40 minutes.And in Transcarpathia, the figure is shifted by half an hour in the other direction - 12:30.Why is noon on the clock does not correspond to the true solar zenith?Here in the laws of nature invaded by policy considerations.To avoid confusion in the schedule of transportation and other inconveniences, states seek to unite all their territories under one time zone, and the only power giants such as Russia or the United States, have to share the land with respect to time.Conventionally, the globe is divided into 24 time zones.Universal being tested GMT.This zero time zone (UT0).All of Western Europe, except Britain, Ireland and Portugal, lives in a zone UT + 1.At the same time the true noon, calculated for the territory located on the borders of Poland and Germany.Thus, in Spain sun culminates when the dial for about an hour of the day.
daylight saving time
If we carry out our experiment with a peg and a compass in the Russian Federation, we will need a lot of patience.Why is that?And you have forgotten a few years ago, the last Sunday of March, all the arrows moved forward one hour?The real time - the winter.And in the summer, even in Moscow comes at noon hour of the day.For the first time so-called "daylight savings" time to enter our territory in 1930 "to save energy."Then in the years of perestroika it was canceled.Then he entered.And then, finally, Russian doctors came to the strange conclusion that since the transition twice a year for the new time adversely affects the human body, it is necessary to leave the summer.Why not winter, left out of the equation.
What is the PM and AM
time a simple man in the street used to be measured in terms of before and after noon.Though we have made, and 24-hour division of the day, most people look at a round dial, divided into twelve sectors.And often indicated by the hour, which shows short needle.At the same time added to the clock.As it turns out, "two o'clock", "three days", "six in the evening."The British Empire was the time taken to indicate otherwise.Namely, guided by noon.Even so hello: «Good afternoon!» - This means "good poslepoludnya you."Such vremyaischislenie survived and now, moreover, it has been applied in the countries of former British colonies.That's where you can find such strange expressions as 8 AM and 3 PM.Translated into Russian, it means eight in the morning and three in the afternoon.Tradition divide time until noon and then come from the medieval Latin.This is evidenced by the abbreviation.Thus, AM is an abbreviation for ante meridiem (until noon).A PM, respectively, by the Decree of the time interval between 12 o'clock in the afternoon and midnight.
