Ledi's - Cross Staff & Back Staff Geocoin

reist immer mit mir

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The backstaff

is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon. When observing the sun, users kept the sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis who described it in his book Seaman's Secrets in 1594.

The cross staff

The term Jacob's staff, also cross-staff, a ballastella, a fore-staff, or a balestilha, is used to refer to several things. This can lead to considerable confusion unless one clarifies the purpose for which the object was named. In its most basic form, a Jacob's staff is a stick or pole with length markings; most staffs are much more complicated than that, and usually contain a number of measurement and stabilization features. The two most frequent uses are:

• in astronomy and navigation for a simple device to measure angles, later replaced by the more precise sextants;
• in surveying (and scientific fields that use surveying techniques, such as geology and ecology) for a vertical rod that penetrates or sits on the ground and supports a compass or other instrument.

The simplest use of a Jacob's staff is to make qualitative judgements of the height and angle of an object relative to the user of the staff.

The origin of the name of the instrument is not certain. Some refer to the Biblical patriarch Jacob, specifically Gen 32:11. It may also take its name after its resemblance to Orion, referred to by the name of Jacob on some medieval star charts. Another possible source is the Pilgrim's staff, the symbol of St James (Jacobus in Latin). The name cross staff simply comes from its cruciform shape.

The original Jacob's staff was developed as a single pole device in the 14th century that was used in making astronomical measurements. It was first described by the Jewish mathematician Levi ben Gerson of Provence. However, its invention was likely due to Jacob ben Makir who also lived in Provence in the same period.