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Parts of the Astrolabe:
The Back

Mater: The body of the astrolabe on whose back side are engraved calendar and degree scales, diverse instruments, and sometimes tables.

Zodiacal calendar: A circular scale divided up into the signs of the Zodiac and their degrees through which the Sun moves during the year.

Civil calendar: A circular scale divided into months and days. It is offset (eccentric) to the Zodiacal calendar.

Circle of degrees: A divided scale along the edge of the mater used with the alidade in measuring the angle between two objects, such as the altitude of a star above the horizon or the angle between two landmarks.

Alidade: A sighting ruler that rotates around the bolt. It has a pair of pinhole sights that stand perpendicular to it. It is used as an index to align civil dates with Zodiacal signs and degrees, and as a sighting device to observe the positions of objects and measure the angles.

Shadow square: A surveying instrument used with the alidade to measure relative proportions of one length to another—for example the height of a tower to the distance of the observer from its base.

Horary quadrant for unequal hours: Used with the alidade to find the time using a system of seasonal, unequal hours that divide every day and night into twelve hours.


Inv Number: DW0594
Date: second half of 16th century?
Maker: French

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