Planisphere Mk. 1

Astronomy

Accession Number: 2018.ast.60.1-3 (DAA-0059)

Description:

These are three nearly identical planispheres stored in flat black faux-leather cases. Two of the three cases (60.1-2) are marked “PLANISPHERE” in silver lettering. Each planisphere consists of a variable number of pieces. Each contains a backing piece, which is a metal square with a folded over rim to allow the mounting of other pieces into it. Each of these has a rotating plastic disk mounted in the centre which depicts a number of celestial objects and constellations. Around the edge of this disk, a scale is divided into 360 degrees.

The other plastic pieces, of which there are between four and one in each case, are roughly square, with a roughly semi-circular cutout at the top. This is to enable the rotating disk to be turned when these pieces are overlaid on the top. Each of these pieces has a clear elliptical panel onto which are printed elliptical rings and degree divisions for every ten degrees.

Each overlay piece gives instructions for its use and indicates which latitudes the overlay is for use in. The latitudes on the surviving planisphere overlays are: N25°-35°, N45°-55° and N55°-65°.

Primary Materials: Metal: Iron Alloy; Plastic

Markings:

On two of three of the case, in silver printing: “REF. No. 6B/153
PLANISPHERE MK.1A
THE BRITISH ENGRAVING AND NAME PLATE MANUFACTURING CO.
SERIAL No.3979/40”

On each of the overlay pieces: “

Dimensions (cm):

Cases: Height = 3, Width = 33, Length = 34.

Function:

A planisphere is an analogue computing instrument design to aid with navigating using the stars. The clear plastic overlays for each latitude are laid over the star chart, which can be turned to show the sky in any direction at a certain time of year.

Condition:

Poor: The faux-leather (plastic) cases of each of the planispheres is decaying and, with 60.2 and 60.3, has become adhered to the contents. With 60.1, the back of the case at one point was lying on paper and paper has become adhered to the back surface of the case.

60.1’s planisphere pieces are intact, although the overlays for one latitude set is missing. The plastic of these pieces is weeping and should be handled with care to avoid smudging of the ink. The plastic of each piece is warped. It is flexible, not brittle, but delicate.

Manufacturer:

British Engraving & Nameplate Manufacturing Company

Date of Manufacture: 1938-1964

Provenance:

The labelling on the cases and parts of the planisphere indicate that these pieces were manufactured for, or once in the ownership of, the British Air Ministry.

This object was likely moved from the David Dunlap Observatory in Richmond Hill in 2008, upon the sale of the observatory. It was stored at the Department of Astronomy and Astrophysics until 2017, when it was moved to a new storage location in McLennan Physical Laboratories.