File:Post-Medieval nocturnal (FindID 529782).jpg

English: An incomplete cast copper alloy pocket nocturnal: "an astronomical instrument for telling the time at night" (MDA Archaeological Objects Thesaurus 1997, 101). The object which has been deliberately cut would have been circular in plan and is now triangular in plan and flat. There is a small perforation which would have been in the centre of the object for a needle. The needle is present and separate. One end which would have attached to the object is perforated. The needle is D-shaped in cross-section. The needle measures 18.34mm in length and is 5.30mm in width. File marks can be seen on the needle.

The upper surface is marked out with very finely incised radial lines. The object has a series five short lines which are divided by longer lines. When complete it would have been subdivided by concentric circles and radial lines, each containing the initial of a month of the year executed in punched dots and lower case black-letter script, arranged anti-clockwise. Between each pair of longer radial lines are inscribed letters which are the initials of the months. The rear of the object is flat. The object has a dark green patina.

Nocturnals were used as an instrument to tell the time at night with the help of the stars. One of the most important features of a nocturnal is the central hole.

It is likely that the nocturnal would have formed the lid of a compendium which also included an equatorial sundial and a magnetic compass. The markings served both to set the calendar date and also indicate the time (at night) in 20-minute divisions, (peers comm. Dr J Davis).