Equinox, me and my shadow. What time is midday?

Many will also recall that:

1. At noon, the shadows are the shortest, and at the equator they generally hide under your feet. This property of midday is remembered, if not from school, then at least from the name of the once popular movie “Shadows Fade at Noon”.

2. At noon, the sun is exactly in the south, which allows you to navigate in unfamiliar terrain, having a watch (or watching the shortening of the shadow).

It must be said that if we did not live in a particular state with its government, laws and decrees, but somewhere on an uninhabited island, preferably without contact with the outside world, then noon would really occur at twelve o'clock in the afternoon.

What makes it so clear? On the day of the spring or autumn equinox, the length of the day is equal to the length of the night. There are 24 hours in a day, of which 12 are light and 12 are dark. The sun rises at 6 in the morning and sets at 18 in the evening. 18 - 6 = 12. Here it is noon!

The next day after the equinox the sun rises a few minutes later (go earlier, depending on the season) and rolls as many minutes earlier (or later), but the middle will still have to be at 12 o'clock in the afternoon. And so all year round. On a desert island.

Simple common sense is good because it is easy to verify. So let's check when it is midday in our area. We use for this the properties of the half day 1 and 2.

At 11.45 we will hammer a long nail into the table, which is on a relatively flat surface, and we will set a precise compass away from the nail. At 11.50 we mark with a pencil on the surface of the table the position of the shade from the nailhead. And after that we will draw on the table a line pointing to the south. At 12.00, we will again mark the position of the nail shadow, the shadow has become a little shorter. But the sun is still far from the south! Suspicious. 12.10 - the shadow becomes even shorter! 12.20 - even shorter, 12.30 - still. It becomes clear that: either we are not on an uninhabited island, or the properties of the noon are “wrong”, or the afternoon has not yet arrived. Common sense tends to the last assumption (not to mention the first).

Inquisitive and patient will continue to measure the shadow, and he will need a lot of patience, because the shadow will be the smallest only in an hour and a half, and then the sun will crawl, finally, to the south. What is the matter?

First, we did not consider summer time. In the spring, everyone moved the clock forward an hour ahead and immediately forgot about it. Now, noon began to come (in summer time) at one o'clock. But even at one o'clock in the afternoon, our improvised observatory did not record the offensive of half a day.

Secondly, we forgot that we live in a country where the decree time is valid. What it is?

“The decree time was introduced by a resolution of the Council of People's Commissars of the USSR dated June 16, 1930 with the goal of more rational use of the light part of the day and corresponding energy savings. Decree time is more than 1 hour ” - quote from encyclopedia.

It turns out that noon comes in the summer only at two in the afternoon.

During perestroika, on the crest of change, the decree time was canceled (in March 1991). I remember this year very well, it was one of the happiest years in my life. I remember how it became dark in the fall not at four o'clock in the afternoon, as usual, but at three, and nobody liked it. Therefore, the maternity time in the same year was quietly returned, in the confusion of that time very few people noticed. Remember, once the clock was transferred not for an hour, but for two?

What do the data from our observatory show? At 14.00 the shadow is really close to the smallest size, and the sun is close to the southern direction, but again it is not quite accurate. What is the matter this time?

In time zones. Within the same time zone, for the convenience of residents, the time is considered the same. For example, at 14 o'clock Moscow time it happens at the same time in Vyatka and in Pskov, and between them more than 1000 km in latitude.

How much does the sun need to “crawl” a thousand kilometers? About an hour. Anyone who flew from the Far East to Moscow or St. Petersburg knows that “time” isn’t spent on a flight: he flew at ten in the morning local time and arrived at ten in the morning, but already Moscow time, although he sat in an airplane 7 hours And the plane flies at a speed of 900-1000 km / hour. Consequently, the sun moves at the same speed.

In the years of Prohibition, when alcohol was sold only from two o'clock in the afternoon, the “bridge across the Psou River” was known. This river separates Abkhazia from Russia (then the united state of the USSR). There are already two in Abkhazia, shops are trading, and in Sochi there is still only an hour, so the thirsty people run over the bridge over the Psou River. This is an example of how moving a few hundred meters changes the time by an hour.

So the testimony of your observatory, which measures the true time in your area, may not greatly coincide with the zone time of your region.

I carried out similar measurements on the longitude of Moscow, and it turned out that noon occurs between 13.35 and 13.45 (to get more accurate data, you need a very long nail and graph paper). Subsequently, I found data confirming the correctness of my measurements (the exact time of noon in Moscow is at 13.40).

And if you have a GPS satellite navigation device, it will easily tell you the exact onset of the noon time in your area.

So decide what is more interesting, spend time checking the laws of nature with the help of common sense, or spend this time to earn money for an expensive device. And how often do you need to know what time it will be noon?

Watch the video: Lahaina Noon, Subsolar Point - Zero Shadow Day (February 2020).


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