Sea astrolabe
The sea astrolabe , also called sea astrolabe , is an old nautical goniometer for measuring the zenith distances of the stars .
description
.png)
The form of astrolabes used in the observatories with their closed mater offered the wind far too much surface to attack and could hardly be kept in the right plane. That is why the sea astrolab was developed for use on boats in rough water and in strong winds. A wheel-shaped device cast from heavy bronze with four spokes marking four quadrants. Really large, heavier bronze devices are known from the middle of the sixteenth century. By increasing the radius, the reading accuracy of the device has been improved, and the inertia of the large mass has improved stability against wind and swell . Most of them also had a gimbal suspension .
An alidade with a reticle (visor) was attached to rotate around the center . Like the astrolabe used on land, its simple variant developed for seafaring was also held vertically in the meridian plane by hand on a ring specially attached for this purpose , aiming at the star through the reticle (left picture). This only worked at night. During the day, when observing the sun, it was safer and easier to align the shadows of the reticles with the alidade (top right picture).
Today sea astrolabes are very rare devices. In 1988 only 65 specimens were known worldwide. The majority of existing astrolabes were recovered from shipwrecks or found on beaches washed up after a storm.
See also
literature
- Willem Janszoon Blaeu : Le Flambeav de la Navigation , Amsterdam, 1619 in Gallica
- Franz Adrian Dreier: Winkelmessinstrumenten , Kunstgewerbemuseum Berlin 1979, p. 61f
- Alan Stimson: The Mariner's Astrolabe , H & S Publishers, Utrecht, 1988, ISBN 90-6194-017-6 .
Web links
- NMM: Mariner's Astrolabe
- Handels- and Søfartsmuseet på Kronborg: Astrolab
- UNI Frankfurt / M .: Sea astrolab from Vasco da Gama
- Florida Memory: Astrolabe from the wreck of the "Atocha"
- ION Museum: Mariner's Astrolabe
- Maritime Museum in Lisbon: Nautical Astrolabe
Individual evidence
- ↑ University of St Andrews: Mariner's Astrolabe 1616 ( Memento of the original from April 29, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ A. Stimson: The Mariner's Astrolabe. A survey of known, surviving sea astrolabes. Hes & De Graff Pub BV, (March 1988), ISBN 978-9061940173
- ↑ Numismatic News: Mariner's Astrolabe in Sedwick Treasure Auction
