Chronometry

Timing ( timing ) is the indication of measures of time in clear reference units ( units). They often requires the increasingly sharp definition of a time system and includes

• Determining a point in time; In metrology, the determination of true time;
• In astronomy and geodesy to determine the local sidereal time and a location - see also timing

• For example, in physics and kinematics motions, velocities, etc.
• As run-time measurement of signals ( navigation, distance measurement, GPS, etc. )
• For the duration of tasks in everyday life and in the natural sciences
• In Sports measurements with mechanical stopwatch or with light barrier, see Timing

A time measurement is always a comparison of reference points, since there is no direct way to measure time on the basis of external influences, such as the current or the wind speed.

Earth's rotation and the stars

The natural and most important timer to date is the rotation of the earth with their regular alternation of day and night. Since the Babylonians, the day is divided into 24 hours, which since then - has prevailed on all continents - as well as the 7 -day week. The regulations for years and months, however, differ in different cultures.

The bourgeois day ( sunny ) follows from the rotation of the earth relative to the sun, from which arise the 365.24 days of the year. In reality, the Earth rotates 366.24 times a year. Your related to the star angle is called the sidereal time.

The sidereal time at the site is best determined by measurement of star passages in the north-south running meridian plane - about a meridian circle or an instrument passages. Approached this is also possible with a rotating star map. The difference between the sidereal time of two places corresponding to their geographical difference in length, with a longitude difference of the local sidereal time at that is defined at the zero meridian. Since the 18th century is regarded as zero meridian of the Greenwich Meridian (or more precisely the central meridian of the Royal Greenwich Observatory).

To get from the sidereal time on the astronomical local time ( or vice versa), you need the date and longitude. But are still small to make corrections because of the irregularity of the earth's rotation ( DUT 1 ). They are monitored for several decades by a global network of atomic clocks and measuring stations.

Technical timekeeping

More generally, the time measurement includes the methodology and instruments that help determine the absolute time, and the duration of a certain process is measured. Timepiece is generally referred to as clocks. Easiest timepiece as they have been used for thousands of years, for example, are sundials. Just walking watches are called chronometers.

In physics and engineering, it is often "only" measurement of time differences - for example when measuring short distances or for the laser measurement to the moon. Such short time differences are determined by the so-called interval counters.

In turn, companies can timekeeping in addition to technical aspects are also used to determine the working hours ( see Time Clock ), but also a better work scheduling (see Time - Organizer).

History

The first detectable clock was - apart from sundials - a water clock or clepsydra, as used by about 1380 BC in Egypt. It was later used by the Greeks and Romans to capture the time in court. Considered the first mechanical clock a 1250 at the court of Louis IX. developed in Paris device. Presumably, however, the pendulum oscillation processes are as has been used for measuring time thousands of years ago. From the 14th century, the hourglass was used in addition to mechanical mechanical clock as a simple non- mechanical timepiece.

More precise measurements began with Jost Bürgi clock of 1580 for the Observatory Kassel, who had a second hand for the first time - and especially with the development of precise clocks. The 1657 Christian Huygens patented escapement ( balance wheel and hairspring ) improved daily Watches transition to about 10 seconds. The Nuremberg egg was small and useful for everyday life, but about 100 times less accurate. First portable marine clocks developed in 1720 John Harrison; they reached temperature compensation one second per day, making English navigators were the first to stop the star heights accurately and determine the longitude of the vessel.

On Observatories reached around 1800, the exact Grandfather Clocks by evacuated pendant boxes daily range of accuracies of a few tenths of a second. With the eye -ear method as the star positions needed to arc seconds was determined accurately and precisely time systems are established. Portable watches this precision contrast, there was only 50 years later.

Nicolas Rieussec in 1821 developed the first clock with workable stop function, which, however, still had the size of a shoe box. As with Jost Bürgi was again the hobby of a nobleman impetus: the horse race of King Louis XVIII. With the seconds hand a pen recorder was coupled, from which the word chronograph was born: from the Greek chronos (time) and grafẽin (write). The step -accurate pocket watch in 1831 succeeded the Austrians Joseph Thaddeus Winnerl in the form of stopwatch " chronoscope ". Although she had no time display as today's " chronograph ", but next to the stop even a drag indicator for measuring lap times.

Around 1880, the Riefler swing improved time systems at observatories even further in the range of some 0.01 seconds and 1921 the Shortt clock in milliseconds; simultaneously by means of wireless technology (time signal transmitter) was made possible global synchronization of precision timepieces. Later television signals and the clocks of navigation satellites were used for accurate time comparisons. In the 1970s, temperature-stabilized quartz watches had already reached the microsecond, and today's atomic clocks have an accuracy of 10-15, which corresponds to 1 second in 30 million years.

Horology

Horology (from Greek ώρα, " hour, time ", and λόγος, logos, " word, speech, sense " ), and time metrology is the study of the measurement of time.

Time differences and time scales

But ultimately boils down almost every time measurement on detecting time differences. In a time scale ( continuous time, as described above), the current time is added up mostly by integration of elementary time steps - for example,

• By the relatively slow oscillations of the pendulum when the pendulum clock and transfer to gears and display
• By the rapid oscillations of the balance in the mechanical clock and transmission of the vibration amount on the gears (see anchor)
• In the piezoelectric resonant circuit of a quartz watch (see also oscillator )
• By the atomic physics effects in measles and atomic clocks

And even

• In the civil time and calendar calculations by counting the days and its fractions.