Solar time

The term local is used to specify the time of day in several related meanings:

• In its oldest meaning is the local solar time used at a location on the Earth's surface. The indication of the time of day was originally directly related to the position of the sun in the sky and measured by a sundial. Since the solar time on the location on the earth's surface depends, different places (more precisely only places with varying degrees longitude) have a different time of day. Each place had its own, the local time of the place called day time. It is more accurately called also apparent time (LAT ) or true solar time.

• In the since about the end of the Middle Ages measured with mechanical watches day time is the " time team" in the little ones no longer the uneven solar time passing away, but the passing away evenly mechanical time. Time maker in the Great continues to be the sun or a fictitious or mean sun, which runs smoothly through the sky, but also indicates the time of day function of location ( in reality it does the mechanical clock ). It is called mean time (LMT ) or mean solar time.

• With the introduction of zone time, the role of the sun was reduced as a time -maker again. The time zone is at all locations within a time zone equal. Only when changing to a different time zone applies a different time of day, called in memory of the past next time zone and local time. The time zone can depending on how many degrees of longitude, the time zone stretches, differ significantly from the solar time.

The solar time and with it the WOZ and the MOZ change by ± 4 minutes when the longitude by 1 ° decreases to - respectively. After solar time and WOZ at each location 12, it is clock when the sun is going to be highest (more precisely, in the meridian ) is.

Compared to the uniformly moving artificial mean solar has the true Sun at only four days a year, no delay or no flow. In between, the maximum deviation is about -16, 4, -6 and 14 minutes. The corresponding difference between LAT and MOZ is specified by means of the equation of time ZG over the period of one year: ZG = WOZ - MOZ.

Before the introduction of the zone whose time MOZ was used as a standard or civil time in the vicinity of major cities or capitals. There was a hamburger, a Hanoverian, a Berliner, a Munich, a Viennese, a Bernese time and many others. Railway companies took over the default time of the starting city of their lines. Consequently, it was at the station in the target cities in addition to the other standard local time, for example, in Geneva, the Geneva time, the Bernese time for the coming of Bern and the Paris time for the coming of Paris railway. Remedy this deficiency was the main motive for the introduction of time zones with zone time.

The time zone is the legal time of a government, or larger region, is spoken of. It applies equally in all fields that belong to a time zone. A time zone extends in the ideal 15 ° difference in longitude. The difference from the adjacent zone time is usually ± 1 hour. At the edges of an ideal wide time zone, the time zone deviates more than ± ½ hour of solar time. In reality, there are sometimes significantly larger deviations because the time zone is broader and / or inappropriate to the solar time.

Local time (LAT )

The true time is 12 clock when the sun goes through the meridian of the site ( meridian passage ). It is in this moment exactly in the astronomical south and highest on their daily arc. From the North Pole to the South Pole, there is at the same longitude have the same apparent time.

She is also the time to a church steeple, indicating a sundial, as the adjacent sundial.

Because of the elliptical orbit of the Earth around the Sun and the tilt of Earth's axis to the Earth's orbital plane, the true solar time goes by not quite uniform.

Mean time (LMT )

The mean time (or mean solar time ) is a uniformly elapsed time in which, over the year by 12 clock, the average position of the sun over the meridian is exactly. The mean time was originally used only for astronomical observations. For every day they gained only gradually by the use of the invented at the end of the Middle Ages mechanical clock important. Although the mechanical clock was initially not very accurate, but it contains in principle a uniform time scale. Meanwhile, the word " mechanical clock " is considered almost as a synonym for the uniform running time.

With the use of the mean local time ( or the mean solar time ) is only slightly removed from the experienced on-site face the sun. The largest deviation is only about 16 ½ minutes in November ( "Sun 's going on " ) ½ or 14 minutes in February ( " Sun go ").

The artificial mean solar time can only be with an elaborate sundial with automatic correction measure ( see illustration ). An ordinary sundial shows the true solar time, which can be converted by means of, for example, tabulated in astronomical yearbooks values ​​of the equation of time in the mean solar time. The table parameter is the day (date) of the year. The equation of time changes only very slowly over the years.

Time zone

As long distances could be covered in a short time with the advent of the railroad, a uniform for their operators and passengers within a larger area time specification was necessary, the railway time. As such, first served most of the home station of the railway line specified by means of mechanical watches mean time. In the picture above, the deviation of the mean local time in Lauenfoerde / Weser from the reference location Berlin (city center) is specified, installed after 1848. Then there was a unified country time, the basis of most of the state capital, the mean time was ( for example, time in Berlin, Munich period (7 minutes difference), only Prague time then time in Vienna, Paris time, Athens time, Lisbon time, Madrid time, etc.).

The in North America across the continent extending railway lines gave rise to establish comparable time zones. The rail travelers no longer use a single local time, the impractical to several hours differed from the local solar time between the Atlantic and Pacific. They reached after a mean of 15 ° longitude difference a new time zone in which they had the clock to adjust by one hour. This American practice was a model for the global device to each other comparable legal zone times in all states. Due to the smaller expansions in Europe its western part, with the exception of Great Britain, Ireland and Portugal has the same legal time, namely in the time zone with respect longitude 15 ° East (CET). It is identical to the MOZ in places on the longitude.

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The reading on a sundial time was long the most accurate reproducible time scale. Until the beginning of the 19th century sundials were meant when they spoke of watches. Only observatories had high-precision pendulum clocks.

Even after the public use, the mean time had become established as standard, you had to rely on the sundial, as the mechanical watches were still too vague. We used a lunch Weiser (picture left), in order to judge once a day after the central sun. At noon analemma of Weiser could automatically corrected noon local solar time and clock up 12 local mean time read (12 clock WOZ ).

After the introduction of telegraphy was unnecessary lunch Weiser. From central locations for time characters were sent, with which one could correct the mechanical watches. The radio clocks used today are automatically synchronized by such central time signal transmitters with the international time scale highly accurate atomic clocks.