Mariner's astrolabe

The Seeastrolabium, also called Seeastrolab, is an old nautical goniometer for measuring zenith distances of the stars.

Description

The mold used in the observatories of astrolabes with their closed Mater offered the wind far too much attack surface and were hard to keep in the correct plane. Therefore we developed the Seeastrolab for use on boats in rough water and high winds. A cast of heavy bronze, wheel-shaped device whose four spokes marked four quadrants. Really big, heavier bronze devices are known from the middle of the sixteenth century. By increasing the radius of the reading accuracy of the device was improved by the inertia of the large mass, the stability improved against wind and sea conditions. They usually also had a gimbal.

Rotating around the center of an alidade was mounted with a reticle ( visor). As the astrolabe used on land, his simple variant developed for navigation was kept up with hand on a specially mounted ring perpendicular to the meridian plane, whereby the reticle the star sighted ( left). This was only at night. On the day, when observing the sun, it was safer and easier that the shadows of the reticle with the alidade in line you brought ( top right).

Today Seeastrolabien are very rare devices. In 1988, only 65 copies were known worldwide. The majority of existing astrolabes were salvaged from shipwrecks, or found on beaches, washed up after a storm.