Columbus Astrolabe

Replicas and Restorations of Early Instruments by Richard A. Paselk

Richard Paselk, Curator

Columbus Astrolabe

Transitional Mariner's Astrolabe

R. Paselk 1990

Copper and Brass sheet

Since the complex planispheric astrolabe is much earlier than the Mariner's astrolabe, the Mariner's astrolabe is considered to be derived from it. The transitional form of astrolabe would then have the altitude reading scales and an alidade. Only later, with experience, would the cutouts appear to reduce the effects of wind when taking readings on the open sea.

The instrument here is modeled after one claimed to have belonged to Christopher Columbus. It is known the he had an astrolabe, but he apparently found it unusable and navigated without it. Details about the original instrument, including scale drawings, may be found in Alan Stimson's book in References. His scale drawings were used in making this instrument, after scaling them up to life-size. The resulting instrument has the same dimensions and appearance of the original, excepting the thickness of the metal: the mater of mine is made from 14 G copper sheet rather than the thick castings normally used in mariner's astrolabes. A recent article describing the earliest known Portuguese astrolabe found in a 1503 shipwreck from the Fleet of Vasco da Gama shows an instrument only 1.5 mm thick (close to 14 gauge), so my replica may be more accurate than I thought!*

In the discussion below the numbers refer to the parts in the exploded view below:

photo of Columbus astrolabe parts with labels

Materials:

Mater (body of instrument-1): 8 3/4" diameter 14 G copper sheet.
Alidade (2): 14 G brass sheet.
Horse (3): 10 G brass sheet.
Sights (6): 3/16" plate.
Axis pin (4) and rivet for hanger (8): 3/8" dia brass rod.
Suspension ring (7): 1/4".
Washers (5): commercial 1/4" brass.

Construction:

The outline of the mater (1) was transferred from a life size photocopy of the scale drawing from Stimson's book using dividers, after first marking the center with a deep punch prick. It was then cut out using a high quality power "jig-saw" with a metal cutting blade. The final outline was accomplished by hand filing.
The sights (6) were soldered to the alidade (2) with lead/tin solder (I had not yet mastered silver soldering when I made this instrument).
The rivet (8) and axis pin (4) were turned on a lathe to 1/4" leaving a 3/8" head on one end. Two holes were then drilled through the shaft of the pin and expanded and shaped with files to fit the horse.

*David L. Mearns, David Parham, Bruno Frohlich. (2016) "A Portuguese East Indiaman from the 1502–1503 Fleet of Vasco da Gama off Al Hallaniyah Island, Oman: an interim report. " International Journal of Nautical Archaeology. 45. pp 331–350.