The Gnomon - Sundial

C

Candlemas: the festival of the purification of the Virgin Mary, on 2nd February. It also corresponds to the Celtic festival of Imbolic, and is a cross-quarter day.

calendar: a system for counting days and defining the date.

Campbell-Stokes: see sunshine recorder.

Cancer: see tropics.

canting out: see wedging out.

Capricorn: see tropics.

cardinal point (of the compass): North, South, East or West [N, S, E or W]. These points are the intersections of the celestial meridian (N, S) and the prime vertical (E, W) with the horizon. Note that the Latin terms are Septentrio, Meridies, Oriens and Occidens, so that a compass rose on a mediaeval dial simply identifying "S" is ambi guous.

cartesian co-ordinates: see co-ordinates .

celestial equator: the intersection of the extended plane of the Earth's equator with the celestial sphere.

celestial latitude: see ecliptic latitude.

celestial longitude: see ecliptic longitude.

celestial pole: the points on the celestial sphere where it meets the Earth's axis. The stars appear to rotate around these poles.

celestial sphere: an imaginary sphere, arbitrarily large and co-centred with the Earth, on which all the stars appear to be fixed.

centre (of a dial): the point where all the hour lines, and a polar-pointing style, meet. This point does not always exist (e.g. on polar dial and direct E or W dials, the lines meet at infinity). In simple horizontal or vertical dials, this point coincides with the root of a (thin) gnomon. In the case of a thick gnomon having two styles, there are two centres to the dial. The centre is often, but not necessarily, the origin of the co-ordinate system used to describe the dial. See Figure 1.

chapter ring: the ring on a dial face carrying the hour numerals. The term is more widely used for clocks, but it also finds use, for example, on dials with several separate rings for different locations.

chilindrum: see Dial (types of); cylinder ~.

civil time: see Time (types of) civil~.

clinometer: an instrument for measuring the inclination or slope of a surface. Also called an inclinometer.

cloisonné: a term sometimes used to describe the technique of making metal dials by deeply etching the lines and numerals and then filling them with coloured material. It derives from the jewellery method of separating enamels into shallow compartments with metal edges.

co-latitude: equals 90° – latitude.

compass bowl: a bowl sunk into the dial plate of a (portable) horizontal dial to house a magnetic compass.

compass rose: a drawing of the compass directions, showing as a bare minimum the cardinal points, but more usually eight, sixteen or thirty-two points.

compendium: normally used to describe a collection of scientific instruments in one case. Also, Compendium: the journal of the NASS.

conic section: any of the range of geometric curves produced by the intersection of plane with a cone (i.e. circles, ellipses, parabolas and hyperbolas).

co-ordinates: a system of measurements used to describe any point in two or three dimensions.