Astronomical Clock Today, there are three main astronomical system of time measurement:
- Earth's rotation on its axis - universal time UT
- of the Earth around the Sun - ephemeris time ET
- emission (absorption) of electromagnetic waves atoms or molecules of certain substances under certain conditions - the atomic time AT.
On Earth, using universal time is referred to as Greenwich Mean Time. It is a mean solar time to zero (Greenwich) meridian and as the basis of standard time. The mean solar time is set according to the observations of the stars, but not for the sun, and on the angular position of the Earth on its axis, regardless of the speed of its rotation. Ephemeris time is used in celestial mechanics, the study of the motion of celestial bodies.
Atomic time is used in cases demands an extremely accurate measurement of time intervals. Since the speed of rotation of the Earth around its axis is variable, universal time is not strictly uniformly against the ephemeris or atomic time.
The unit used in the daily practice of mean solar time is the mean solar day, which consists of 24 high sunshine hours. One mean solar hour consists of 60 minutes of mean solar, and one high solar minute - 60 of the mean solar seconds. It is assumed that the day starts at midnight.
Local time at a particular point on the Earth depends on its longitude. When moving to the west of the prime meridian, it lags behind the world for 1 hour every 15 degrees of longitude. Not to enter the local time for each degree, and put 24 time zones. When moving from one time zone to another for the minutes and seconds (time) are stored, and the hours vary.
In the North and South Poles meridians converge at one point, and the concept of time zones loses its meaning. Taken so that the poles are presented in the worldwide.
The speed of rotation of the Earth characterized by seasonal fluctuations, and therefore universal time is lagging behind, then ahead of the ephemeral. During the year, these deviations can reach 30 ms.
The amendments introduced in Universal Time Bih (Paris).
Control is performed over time using the clock. The most ancient are the water and the hourglass. The exact definition of time was made possible with the invention of the pendulum clock.
Since the 50s of the last century have given way to a pendulum clock with quartz and atomic clocks.
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The Astronomical Clock of Prague
Each hour a huge crowd gathers to watch this clock trot out its lively cast of characters - including death, avarice and vanity! For more: http://www.gypsynester.com/pc.htm
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