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Because the earth rotates from west to east, it is sooner or later to see the sunrise in different areas at the same latitude. The time in the East is earlier than that in the West. This different time due to different longitudes is called local time. Because the time is early in the east and late in the west, it is 15 in the east and 1 hour in the west.

Two. Calculation of time zone

In order to facilitate the communication between different regions, the international time zone of 1884 is divided according to the unified standard, and the time-sharing method is implemented. According to this division method, every 15 on the earth is regarded as a time zone, and the world is divided into 24 time zones. The local time of the central meridian of each time zone is the standard time zone of that time zone. Time zone calculation is usually divided into the following steps:

1. Calculation of time zone:

If you need a longitude zone, you must first calculate the time zone where the longitude is located. The formula of longitude to convert time zones is: longitude ÷ 15 = m (quotient) -n (remainder) (when n < 7.5, the number of time zones = m, when n > 7.5, the number of time zones = m+65433.

2. Calculation of regional time difference:

If you know the time zone of place A and find the time zone of place B, you must first calculate the time zone difference between the two places. If the two places are on the same side of the middle time zone, subtraction should be used to calculate the time zone difference. For example, the East Eighth District is 6 districts away from the East Second District, and the West Ninth District is 7 districts away from the West Second District. If these two places are on both sides of the middle time zone, you should use addition to calculate the time zone difference. For example, the west sixth district is far from the east sixth district 12 district.

3. Calculation of time zone:

The calculation of time zone follows the principle of [East plus West minus]. When the time of A is known, the time of B is found. Then the time of B is equal to the time of A plus or minus the time difference between A and B (B is in the east of A and B is in the west of A, represented by [-")).

4. Processing of calculation results:

Because the whole day adopts the 24-hour system, if the calculation result is greater than 24 hours, 24 hours will be subtracted. Date plus one day is the required time, and if the calculation result is negative, 24 hours will be added. The date minus one day is the time required. Speaking of new year and month, we should pay attention to big month, small month, normal year and leap year.

Three. international date line

The date line is just the dividing line between today and yesterday. Starting from the prime meridian, if you go eastward to meridian 180, then meridian 180 is 12 hours earlier than the prime meridian. If you go west to longitude 180, then longitude 180 is later than the prime meridian 12 hours. This is longitude 180, but the time difference is 24 hours. Therefore, according to international regulations, longitude 180 is regarded as an international international date line. This is both a day. 12 area is one day earlier than western 12 area. It is worth noting that the international international date line and meridian 180 are not completely coincident. Due to the influence of various countries' territories, international date line in some places has to be changed and bent. The other date line is the 0: 00 date line (or the midnight date line). Between 0: 00 international date line and the meridian of 180 is "today". Go west to 65438.

4. Find the starting point of time calculation

When calculating the time, you can find the breakthrough point quickly and accurately, which can not only improve the speed of doing the problem, but also improve the accuracy of doing it. These methods are as follows:

1. When determining the position according to the termination line:

Because the equatorial region is equally divided day and night throughout the year, the time on the meridian where the equator intersects with the morning line is 6 o'clock, and the time on the meridian where the equator intersects with the dark line is 18 hour.

2. When determining the position according to the direct point of the sun:

That is, the time on the meridian where the direct point of the sun is located is 12, and the time on the other meridian opposite to it is 0 (24: 00).

3. Determine the date according to the end line:

If the terminator line coincides with the meridian, that is, the terminator line passes through the north and south poles, it can be judged that this day is around March 2 1 (vernal equinox) or September 23 (autumnal equinox), and the world is equally divided at night. The local time at all locations on the morning line is 6 o'clock. The local time of all points on the dark line is 18. When the termination line is tangent to the polar circle, if the arctic circle and its northern area are equal,

4. Calculate the length of day and night and the time of sunrise and sunset according to the termination line:

When the terminator line coincides with the meridian, the world is divided equally between day and night, with 12 hours in the day and 12 hours in the night. When the termination line intersects the meridian obliquely, the simple formula is: day length = day radian/15. Night length = night radian/15. Calculation of daily radian: calculate the latitude circle of the place in the daytime hemisphere, that is, the longitude from the intersection of the morning line and the latitude circle to the intersection of the faint line and the latitude circle. Sunrise and sunset.

Verb (abbreviation of verb) clarifies confused concepts.

1. Time zone and time zone:

Time zone is a spatial concept, representing the range of 15, that is, the range of the central meridian from east to west of 7.5. Time zone is a concept of time, which is the universal time of time zone. In this range, the local time of the central meridian is regarded as a time zone.

2. Local time and time zone:

Different meridians have different local time. The local time of the same meridian is the same. There are countless local times in the world, and the time zone is the common time in the same time zone. There are 24 balls.