Noon

The lunch is the time of passage of the sun through the meridian middle of a location on Earth. At this moment the sun reaches its daily peak ( in the nautical " zenith ") and is the zenith of the next.

However, the general use of language usually refers to the time 12:00 clock or a small period of time on both sides.

Astronomical noon

Highest sun ( zenith )

The elevation angle h (or the zenith distance z ) of the sun at noon depends on the season ( the solar declination δ ) and on the latitude of the location B from:

H = 90 ° - z = 90 ° - | B - δ | (angle 90 ° - B is called Kobreite or polar distance ), or   z = 90 ° - h = | B - δ | with -23.45 ° ≤ δ ≤ 23.45 ° For places near the equator (more precisely, between the tropics ( | B | < 23.45 ° ) ), the sun rises twice a year exactly through the zenith, for places within the Arctic Circle, it is also to " lunch " days to months under the horizon.

The shadow of a vertical gnomon ( rod of a sundial ) is at noon at the shortest and assigns north of the Tropic of Cancer due north or south of the Tropic of Capricorn due south. Between the tropics, it depends on the time of year, whether the shade at noon north or south falls.

Time of true noon

The timing of the astronomical noon, the true noon, so 12h apparent time depends firstly on the location and its geographical (more precisely, astronomical ) in length, and secondly, the equation of time is in the calculation (an effect due to the obliquity and the elliptical shape of Earth's orbit ) considered.

Specifically, can the true noon calculated as follows:

Example of Munich city center (geographic latitude 11.6 ° east) on 12 July 2008 ( Z = -5 min): 12:00 00:04 · clock ( 15 to 11.6 ) - ( -0:05 h ) 1:00 = 13:19 CEST clock.

Lunch in other contexts

Commonly, the term is also an intuitive time interval, for example, from 12:00 clock to 14:00 clock. Especially in hot climates, this period includes the midday rest or siesta. Among other things, in the USA and the Federal Republic of Germany, the term is lunch ( noon ) used for the exact Time 12:00 clock, such as opening times ( open: noon - 7 pm ).

The former public timekeeping was predominantly regulated on the basis of astronomical determinations of time for which it, inter alia, in many places was the so-called noon cannon.

In meteorology is not those registered as midday temperature at 12:00 clock, but in most countries, at 14:00 clock. Around this time (or summer time at 15:00 clock ) occurs on average a maximum temperature because warm soil and air only gradually.

In geophysics are magnetic and charge effects the upper atmosphere strongly related to time of day - for example,

• The magnetic Sq variation and
• The ion and electron density of the ionosphere ( TEC see ), which reaches its maximum shortly after the local noon and
• Also for the radio traffic and the cosmic geodesy is important ( eg, GPS and VLBI, monitored including by regular measurement campaigns of the IVS ).