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Deutsches Technikmuseum - January

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The Websites of the donation Stiftung Deutsches Technikmuseum Berlin at a glance:

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The donation contains six locations:

Exhibit of the Month January 2014

Photo: The cylinder on the left is used to set the hour angle, the exact compass direction and the geographical longitude; the right one is for reading the height of the horizon, the elevation over the celestial equator, and the geographical latitude.

The operational Astra-Plot © SDTB / C. Kirchner

The Astra-Plot – a "three dimensional slide-rule" for celestial navigation, 1969

The company Anschütz, which is headquartered in Kiel, has been making nautical instruments since the 1920s after having gained worldwide recognition for their remarkable gyrocompasses. In 1969, Anschütz developed and produced the navigation sphere Astra-Plot.

Five specific data to specify the location of a ship

The device specifies the location of a ship to within one nautical mile without the need of any paper calculations. Five specific data are required: First, the approximate position of the ship as determined by the compass bearing and travel time; second, the height of a star above the horizon, preferably the sun, as measured by a sextant; third, the exact compass direction of that star as determined by an amplitude compass; fourth, its hour angle as determined by the time of day and a nautical chart and, fifth, the angular distance of the star to the celestial equator as determined by the nautical chart or the star map.

Following the "recipe book" type instructions exactly, those five data must be entered by turning two large configuration cylinders whereby the scales, vertical curves and the so-called meridian swing arm all engage with one another in an appurtenant way and move in unison. The eventual reading on the cylinder then shows the exact position of the ship. With a little practice, the whole operation could be completed in two minutes.

Terminus of classical star-based navigation

Only 30 Astra-Plots were built; they were to be sold at a purchase price of 30,000 German Marks each. However, they were never offered for sale because by the time they had been produced satellite navigation had already taken over the marine navigation market. In this respect, the Astra-Plot was the high point and the terminus of classical star-based navigation.

The Deutsches Technikmuseum purchased the device in a private sale in 2013.