Local time


Locality When is a change in the form of the sun, he uses a consistent time in the specified longitude range, his consistency is only Depending on the accuracy of the measurement.

Local usually gradually be adopted from the beginning of the 19th century, and these regions no longer use local sun or daily time until each country will be customized in a variety of different forms. The standard time means that the same time is used in some areas - usually, not from the Greenwich standard time is the local time of the main area in the region as standard time. The difference between the local usual and the sun is equal to the equation of time.

Sun day

Sun day (English: Solar Day ) is based on the sun movement, the defined time can be divided For the , the sun day and Pingyang Day .

One of the sun days is called a "day", a "day" or a "day and night".

Local time

Looking at the Sun Day

The sun day is based on the true sun definition, that is, the real sun has two consecutive times. That is, the time interval from the upper day or down to the next day can be used to measure (upper day).

Due to the following two reasons, the length of the sun will constantly change every day.

  • First, the earth's track is an ellipse rather than a round circle, so when the earth is close to the sun, the speed will speed up, the speed is the fastest at the time of recent point; it will be reduced Slow, the speed is the slowest at the distance (refer to Coppler Planet Law).

  • Second, because the inclination angle of the earth's self-rotating axis, the sun running on the yellow road is sloping on the earth's oriental equator, when the sun is in two points, There is an angle when crossing the equator, so the running speed projected on the equator is smaller than the average speed; when the sun is in the point, his movement direction is parallel to the equator, so the projected running speed is higher than the average speed (reference Returning year). Therefore, depending on the sun day in March (26-27) and September (12-13), it is shorter than in June (18-19) or December (20-21). The length of these dates is gradually changing between points, points, far days, and near-days.

Pingyang Day

Pingyang Day is a reference point with a flat sun, with a flat sun for two consecutive times Under certain space, the time interval is taken, take 24 hours to turn 360 ° 59 '. More specifically, Pingyang Day is the time to display the clock via the average sun, the average sun is visual, and the average sun is viewed.

The length of the Pingyang Day is a fixed 24 hours, which will not change due to the change in day and night. Looking at the length of the sun, it will be different from the flat sun day (86,400 seconds), and the adjacent per day can be shorter for 22 seconds or 29 seconds. Because this extension or shortened will continue for a period of time, it will be a 17-minute or delayed 14 minutes earlier than the flat sun day. Because these periods are periodic, the difference between the time when the sun is sunny, and the difference in the sun is equal.

There are many ways to simulate (display) Pingnshi, the first use of leaks or water clocks, almost 4,000 years to the mid-2000. Before the year before the middle of the year, the water clock can only be adjusted on the sun day, so it is better than the day of continuing to use at night, it will not be better than the sunshine.

However, the sun relative to the star is always moving towards East in the zodiar, so the weekly mid-term motion relative to the stellar can be used to determine the premium day, The error rate of the clock. Babylonia's astronomers have known the average time difference and how to use the self-rotational rate, star of the star, to correct to obtain a more accurate time than the water clock. This ideal star is also used in the description of the planet, the moon and the sun.

In the early 20th century, the accuracy of the mechanical clock has not been accurate than the starry clock displayed by the earth, even if it is today, the accuracy of the atomic clock is more stable than the globe, the starry clock is still being Used to calibrate the sun day. At the end of the 20th century, the rate of self-rotation of the earth is changed to the radio power of the alien, and the ratio of the external wireless power supply is also converted. Difference between Pingyang and Coordinated the World Whether it is necessary to do a basis for leap second adjustment.

Related entries

  • Japanese

  • time zone

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