de Rojas-type astrolabe
Date1551
Inventory NumberDW0592
ClassificationAstrolabe
Subject
Maker
Anthoine Mestrel
fl 1551
Cultural Region
Place of Origin
Dimensions13.9 x 10.1 x 1.6 cm (5 1/2 x 4 x 5/8 in.)
pouch: 20.6 × 12.7 × 2.2 cm (8 1/8 × 5 × 7/8 in.)
pouch: 20.6 × 12.7 × 2.2 cm (8 1/8 × 5 × 7/8 in.)
Material
Accessoriesold velvet pouch
DescriptionThis brass astrolabe is of the de Rojas type and uses an orthographic projection of the celestial sphere. The orthographic projection of the celestial sphere was first applied to astrolabes by Regiomontanus, who may have learned of it from his teacher, Georg Peurbach. Regiomontanus called it the "organum Ptolemei." Juan de Rojas y Sarmiento studied with Gemma Frisius in Louvain, and published a book on this form of astrolabe in 1550.
On the front, there is a de Rojas orthographic projection of the celestial sphere between the Tropics of Cancer and Capricorn. The Arctic and Antarctic Poles are marked in Latin. The disk with the project has pointers at each pole and rotates . The pointers read of latitude along the limb. Latitude is marked from 90-0-90 degrees every 2 degrees. 0 is at the top below the throne. A bar goes across the projection on the disk and indicates the viewer's horizon and the lines of the rising sun, dawn, and dusk. A "TRIGONVS" has a hole for a plumb line (missing) and two sights for observing the sun's shadow.
The bolt is ornately shaped and pierced. The throne is engraved with a Celtic knot on a disk above a blank shield a scrolling acanthus leaf (or wing) on each side.
On the back of the astrolabe, the limb is divided into signs of the zodiac. Each sign is indicated by its symbol and subdivided into 0-30 degrees, every 2 degrees. These divisions also serve for the altitude measured by the alidade. Inside the zodiacal calendar circle and eccentric to it is a civil calendar circle divided into months. Each month is divided into days 0-30 (or 28 or 31) with divisions every 2 days. Months are labeled in initials.
In the upper right and left quadrant of the astrolabe, there are horary quadrants for unequal hours. They are marked 1-6 and 6-12. A sun face surrounded by stars fills in the center.
In the lower right and left quadrants is a shadow square with sides divided into 12 parts. It is labeled "VMBRA VERSA" (with a backwards "s") and "VMBRA RECTA."
On the front, there is a de Rojas orthographic projection of the celestial sphere between the Tropics of Cancer and Capricorn. The Arctic and Antarctic Poles are marked in Latin. The disk with the project has pointers at each pole and rotates . The pointers read of latitude along the limb. Latitude is marked from 90-0-90 degrees every 2 degrees. 0 is at the top below the throne. A bar goes across the projection on the disk and indicates the viewer's horizon and the lines of the rising sun, dawn, and dusk. A "TRIGONVS" has a hole for a plumb line (missing) and two sights for observing the sun's shadow.
The bolt is ornately shaped and pierced. The throne is engraved with a Celtic knot on a disk above a blank shield a scrolling acanthus leaf (or wing) on each side.
On the back of the astrolabe, the limb is divided into signs of the zodiac. Each sign is indicated by its symbol and subdivided into 0-30 degrees, every 2 degrees. These divisions also serve for the altitude measured by the alidade. Inside the zodiacal calendar circle and eccentric to it is a civil calendar circle divided into months. Each month is divided into days 0-30 (or 28 or 31) with divisions every 2 days. Months are labeled in initials.
In the upper right and left quadrant of the astrolabe, there are horary quadrants for unequal hours. They are marked 1-6 and 6-12. A sun face surrounded by stars fills in the center.
In the lower right and left quadrants is a shadow square with sides divided into 12 parts. It is labeled "VMBRA VERSA" (with a backwards "s") and "VMBRA RECTA."
Signedon back of the mater: PARIS 1551 / * ANTHOINE * / * MESTREL *
Curatorial RemarksXRF analysis of the metals was done by Katherine Eremin and Sara Schechner in August 2007.
FunctionThis form of astrolabe was used for time finding and surveying. One could also use it to measure the altitude of a celestial body.
ProvenanceDavid Wheatland acquired December 25, 1953.
Antonius Giamin
Date: early 20th Century
Object number: DW0590
Leon Barritt
Date: 1906
Accessories: 1937 booklet in file
Object number: DW0650