Celestial Planisphere Called Astrolabe for Latitude 41

This small,,square paper instrument is the oldest surviving Anglo-American star map. It was drawn by hand in 1780 by Simeon de Witt, geographer to George Washington and the Continental army. It shows the bright stars visible in Ringwood, New Jersey, where he was stationed.

The upper section of the instrument consists of three parts. The topmost is a rotating disc with an oval cut out of it. The four cardinal points are indicated on the oval. The edge is divided to degrees, with every 10 degrees marked. Below the oval opening is a perpetual calendar for the years 1781 to 1826. This is labeled: 1780 (/) Simeon DeWitt fecit. (/) The Days of the Months for ever. Below the top disc is a rotating disc, attached to the base, that has a star map on it. The map shows first through fifth magnitude stars (first magnitude stars are indicated by a seven-pointed star, second magnitude by a six-pointed star, 3rd magnitude by a five-pointed star, fourth magnitude by a x and fifth magnitude by a dot). Stars are arranged in constellations. In additiion to Ptolemaic constellations, the constellations Lynx, Columba Noachi, Leo Min, Monocerus, Camelopardalis, Mons Menalus, and Antonius are represented. The 1596 Nova in Cetus and the Via Lactea also are shown. The ecliptic, polar circle, Tropic of Cancer, equator, and Tropic of Capricorn are represented by circles. The edge of the disc has two scales, one of days of the year and the second of degrees of the zodiac.

The third part of the instrument is a square base marked at the top "ASTROLABE FOR Lat. 41." On the left side is a list of sixteen stars of first magnitude. On the right is a list of the constellations that contain these stars. The reverse of the base contains a disc allowing one to determine phases of the moon for dates from 1781 to 1834.

Reference:

P.A. Kidwell, "The astrolabe for latitude 41°N of Simeon de Witt: an early American celestial planisphere," Imago Mundi, 2009, 61, pp. 91-96.

Currently not on view