Noon mark
A lunch Weiser shows with the help of the sun at noon. The sun is - displayed in the central projection on a mostly flat surface - like a sundial.
A fixed lunch sage is used, among other things, to indicate the time of noon or the passage of the sun through the meridian. In general, the elevation angle of the noonday sun is measured with it, from which the anniversary date, as in the Solarium Augusti results. This instrument is called since its excavation Meridian, a term that has become established as a synonym for at least great lunch Weiser.
Using a portable lunch Weiser the south direction or the direction can be determined at noon. A corresponding measurement method is the Indian circle.
Often a lunch Weiser is also known as lunch sundial, although his mere display of noon ( ways of noon ) is not a function of a clock. View fairs and as a date but can be over the year variable height of the sun, for which a common name is Zodiakuhr.
A special variant of the lunch Weiser shows on a analemma scale -like loop at the Middle noon. This was until the beginning of the 20th century mechanical clocks - for example on railway stations - adjusted.
Gnomon
The oldest lunch Weiser was the gnomon. It was used to determine both the direction and as a main component of a permanently built astronomical instrument. In the first case ( portable lunch Weiser, Indian circle) he needed to insert only one sunny day in the soil. In the second case it was fixed in the soil and marked permanently with him certain north-south direction as a meridian line on the ground " smudge-proof ".
The astronomical measurement is made at the moment of the sun is. Is read off the shadow length of the gnomon as a value for the elevation angle of the sun h, from which the days of the solstices and equinoxes are the recognizable. From the extremes of the elevation angle gives the angle of the ecliptic. The elevation angle of the sun to the Äqinoktial - days is a measure of the latitude of the place of measurement.
From the astronomical instrument Gnomon later became a full sundial of the except the moment of noon all times of the day are read. With Gnomonik today is meant by the sundials primarily teaching.
Meridiana or Meridian
From the 16th to the 18th century monumental lunch Weiser were established in order to carry out astronomical measurements preferably in some Italian and French cathedrals. Such lunch Weiser is Meridiana Italian and French called Meridian. It was the time before and after the Gregorian calendar reform in the Catholic Church began to abandon their hostility towards science.
The image of the sun done with a local hole - gnomon, the high is located in a south wall under the ceiling. The scale ( meridian ) extends on the ground almost the entire length of the nave. A hole - gnomon is necessary because a light spot can produce more concentrated than a shadow point at great distances.
In Italy Meridianas were numerous. The in the cathedrals of Florence ( set of Toscanelli ) and Milan were set up in 1475 and 1786. The Dominican monk Egnatio Danti designed several Meridianas, the best known of him was the established about 1575 in the Basilica of San Petronio in Bologna. Due to a few millimeters in size hole gnomon in the dome of the basilica fell to a 70 -meter-long, recessed into the bottom brass band around noon a ray of sunshine. On the tape, one could read the calendar and the signs of the zodiac. The readings of Danti at such a meridian line data made the deviation of the Julian calendar from the sun's path clearly and directly led to the reform of the calendar by Pope Gregory XIII. The Meridiana by Danti in Bologna was faulty. On the occasion of conversions was the astronomer Giovanni Domenico Cassini in 1655 there a new install Meridiana, which still exists today.
Méridiennes for the same purpose are known from the churches of Saint Sulpice in Paris and Saint Michel in Brussels and from the Old Hospital in Tonnere / F. Confusion is possible with a larger number of simplified sundials on exterior walls, which originated in the 18th and 19th century in Alsace. They are referred to in the literature as Méridiennes.
Lunch Weiser for directing Clocks
The mechanical clock was not long repress despite their great advantage of the independent functioning of the weather, the sundial. The most important reason was that the sundial measure accurately. You had for a long time significantly before the judge or ENGAGED release blades watches with the help of a sundial.
As the judging was only necessary once per day, lunch Weiser were used the most were at a public building, such as churches, town halls and railway stations. They were until the advent of electrical communications technology in the 19th century in use. After that, specify a sufficiently precise mechanical clock central time of day could be made known nationwide. The use of the middle period was necessary at the latest, with the advent of the railway in the mid-19th century. Lunch Weiser were therefore also preferred because sundials, which are designed for Mean Time throughout the day were eliminated because of their complexity. This lunch Weiser were also provided with hole gnomon. In sundials it can not be applied because one would have to turn continues it during the day so that he is transverse to the sun.