Ferro meridian
The Ferro meridian , also known as the Ferro meridian , was the most common prime meridian in Europe from ancient times until 1884 . The coordinates of numerous sea and land maps up to the 19th century are aligned with him. It refers to the Canary Island "Ferro" ( Spanish El Hierro ) at 17 ° 40 'west longitude of Greenwich. The meridian of Ferro is historically related to the meridian of Paris .
history
Definition
For the first time around 100, Marinos von Tire set the insulae fortunatae ( Canary Islands ), the western end of the then known world, as a reference point. However, this definition owes its implementation to the takeover by the important astronomer Claudius Ptolemy in 150. However, it was of more theoretical importance, since Ptolemy's work referred to his hometown Alexandria, whose position he set at 60.5 °, which in no way reflects the correct position of the Canaries. With the Middle Ages and its cycle maps , meridians became meaningless, the Canaries disappeared from the known world of Europe. The later postage cards did not show any geographic coordinates either.
With the rediscovery of the Canaries in the 14th century and the subsequent Renaissance , the Ptolemaic ideas were revived and the westernmost island Ferro (today El Hierro ) was established as the prime meridian. In connection with the voyages of discovery and the establishment of observatories in Europe, initially without lens instruments, the number of competing zero meridians rose from the 16th century. However, most of them only achieved local or national importance. The fact that the meridian of the magnetic pole , which initially appeared as a possible natural definition of the prime meridian, was apparently only a little to the west also helped Ferro's retention . Another advantage of this length count were positive values for all of Europe. In April 1634, a scholars' congress of all seafaring nations confirmed the prime meridian of Ferro and at the same time fixed it more precisely to Punta Orchilla , the western tip of the island.
Until then, the technical errors in determining the length had been several degrees: Ptolemy determined the length of the Mediterranean Sea to be 62 °, Mercator gave it in 1554 to be 52 °, in fact it is 42 °. The telescope, known from around 1610, made it possible to reduce the error to 10 to 12 minutes by observing astronomical events, especially the orbits of Jupiter's moon, for which tables were available from 1668, while observing at the reference point to 2 to 3 minutes. This made well-developed observatories on the reference meridian even more important. The forerunner was Brahe's Uranienburg ; the Paris Observatory from 1666 and the Royal Greenwich Observatory from 1676, all of which led to new meridian systems for practical reasons. The construction of a large observatory on Ferro was unthinkable. Since the Ferro meridian was still not to be abandoned, after Louis Feuillée determined the length difference to the Paris observatory in 1724 at 19 ° 52 'to 20 ° 06', the consensus was that Ferro should be exactly 20 ° west of the Paris observatory. Thus the prime meridian of Ferro had become a hidden prime meridian of Paris. Until then, a Paris – Ferro length difference of 22 ° 30 ′ had been calculated.
Replacement by Greenwich Prime Meridian
As a result, many national zero meridians were replaced by Ferro or traced back to Ferro, so that from the middle of the 18th century only Ferro and Paris on the one hand and, initially to a lesser extent, Greenwich on the other were more important. Shortly afterwards, from the last third of the 18th century, reliable length determination was also possible at sea by recording sufficiently accurate lunar distances in lunar tables and using sufficiently accurate chronometers . Exact length information on nautical charts was therefore also required. Since the sea power Great Britain was leading here, the prime meridian Greenwich prevailed on nautical charts. It was not until 1884 that Greenwich was agreed upon as an international recommendation as a reference point and then quickly established itself; it became binding at the 1913 International World Map Conference.
Use today
Even after the map series had been changed, the prime meridian was mostly still used by Ferro within the surveying authorities. In Germany, the prime meridian of Ferro was replaced by that of Greenwich in 1923 as part of the preparations for the transition of the national survey to Gauß-Krüger coordinates . For this purpose, the rounded value of 17 ° 40 ′ was subtracted from the previous length values in order to be able to retain the previous sheet section of the topographic maps. In Austria, all map series have already been converted to UTM with the reference meridian Greenwich, while the Austrian land surveying still refers to the prime meridian of Ferro ( Federal Office for Metrology and Surveying ). By referring to Ferro, you can get by with a total of three meridian stripe systems for all of Austria (28 °, 31 ° and 34 ° east of Ferro), with reference to Greenwich it would be four. The conversion to Greenwich lengths was done with the
- internationally standardized value of 17 ° 40 ′ 00 ″ (see also Hermannskogel and Rauenberg ),
- while the older value of 17 ° 39 ′ 46.02 ″ resulted from the European length adjustment by Theodor Albrecht (around 1890). Because of an absolute deviation from the perpendicular of 13 ″ to 14 ″ in Vienna and Berlin , the round value was ultimately determined.
literature
- Wolfgang Seidel : Great moments. The adventurous story of the discovery and measurement of the world . Eichborn, Cologne 2014, ISBN 978-3-8479-0574-5 ; therein the subchapter Ferro-Meridian , pp. 63–64.
- Gustav Forstner: Length errors and starting meridians in old maps and position tables. Dissertation, University of the Federal Armed Forces Munich, Faculty of Civil Engineering and Surveying, Geodesy and Geoinformation course, Neubiberg 2005 (= series of publications / Geodesy and Geoinformation course, University of the Federal Armed Forces Munich, issue 80. Also online as PDF , athene-forschung.unibw.de ).
Individual evidence
- ↑ Carte particulière des environs de Paris ... Map of the area around Paris from 1690, with the meridian of Paris at 22 ° 30 ′ of the Ferro meridian
- ↑ 3-D reference systems in Austria. Retrieved June 2, 2018 .
Web links
- Heinrich Busch: The zero meridian. seefunknetz.de, 2000 (with maps)