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This allowed mariners to figure out the time and magnetic variation in a single action. These are likewise called "sundial compasses". Structure and function [edit] The 3 rings are oriented with regard to the regional meridian, the world's equator, and a celestial item. The instrument itself can be used as a plumb bob to align it with the vertical.

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This fixes the orientation of the instrument in all three axes. The angle in between the vertical and the beam offers the solar elevation. The solar elevation is a function of latitude, time of day, and season. Any among these variables can be determined using huge rings, if the other 2 are understood.

Use as a calendar sundial [edit] When the solar time is precisely midday, or known from another clock, the instrument can be used to determine the time of year. The meridional ring can operate as the gnomon, when the rings are utilized as a sundial. A horizontal line aligned on a meridian with a gnomon dealing with the noon-sun is described a meridian line and does not show the time, however rather the day of the year.

A set meridional ring on its own can be used as an analemma calendar sundial, which can be read just at twelve noon. When The Latest Info Found Here of the rings are lined up so that they seem in the exact same, or nearly the exact same, location, the meridian determines itself. [] Meridional ring [edit] The ring is positioned vertically, then rotated (relative to the celestial object) till it is parallel to the regional north-south line.

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Since the instrument is often supported by the meridional ring, it is typically the outer ring, as it remains in the traveller's rings illustrated above. There, a sliding suspension shackle is connected to the top of the meridional ring, from which the entire gadget can be suspended. The meridional ring is marked in degrees of latitude (090, for each hemisphere).

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This tilts the equatorial ring so that it lies at the same angle to the vertical as the local equator. Equatorial ring [edit] The occupies an airplane parallel to the celestial equator, at right angles to the meridian. It is lined up by being connected to the meridional ring at the marking for latitude zero (see above) being lined up to the declension ring, which is lined up to the celestial item.