This instrument is based on the earliest known extant mariner's astrolabe. It was discovered in 2014 as part of the archeological excavation of the wreck of two  Portuguese naus (heavy, 3-4 masted sailing vessels) the Esmeralda and the Sao Pedro, lost to a heavy wind in May 1503 off the coast of modern Oman.* The two ships were part of Vasco da Gama's fourth armada, departing Portugal for India in 1502. From the markings on the astrolabe and the date of departure for the armada, the authors of the description of this instrument date its manufacture between 1496 and 1501. This artifact is the only solid mariner's astrolabe with solid provenance and date. It is the earliest known mariner's astrolabe and the only instrument of this type decorated with national symbols.

Maker's Notes

The instrument is 175mm in diameter and 1.5–2mm thick (6.89" dia. & about 14G). In the paper describing this instrument the authors assume it is a casting due to the thickness at the decorations, however, I am assuming for my recreation that the decorations and center area were made separately from the body and later attached as seen commonly in European planispheric astrolabes made during the medieval period.

Laser scans of the original astrolabe found graduations at 5° intervals in the upper right quadrant of the disc. There were no minor graduations, nor was there evidence of circular arcs or figures. However, the poor condition of the surface due to corrosion leaves it uncertain as to the original  layout.l As a result, in my recreation I am "engraving" my astrolabe based on my literature research on both planispheric and mariner's astrolabes using images and descriptions to guess what the original astrolabe was likely to have looked like. I am also using my experience intuition as a recreator of early navigational and astronomical instruments to determine its final appearance. 

Design constraints/decisions:

• Full circles inscribed completely around the astrolabe to enclose graduations—in all of the examples of mariner's astrolabes the I have been able to look at good pictures of , the arcs for the graduations have extended to full circles whether the instrument is graduated around the full circle, just the upper two quadrants or only one of the quadrants. In addition, circles are traditional if only because of their special status as "perfect" shapes.d

• Graduations are made to five degrees for major graduations (about 1/2" long) and to one degree for minor graduations (about 1/8" long). In this case on the original artifact only five degree marks are discernable, with graduation lines up to about 13 mm (1/2") long.

• See Mearns, David L., Warnett, Jason M. and Williams Mark A. "An Early Portuguese Mariner's Astrolabe from the Sodre Wreck-site, Al Hallaniyah, Oman. The International Journal of Nautical Archeology (2019) 00.0: 1–12.