The York Minster astronomical clock is a memorial to the airmen operating from bases in

Yorkshire Yorkshire ( ; abbreviated Yorks), formally known as the County of York, is a historic county in northern England and by far the largest in the United Kingdom. Because of its large area in comparison with other English counties, functions have ...

Durham Durham most commonly refers to: *Durham, England, a cathedral city and the county town of County Durham *County Durham, an English county * Durham County, North Carolina, a county in North Carolina, United States *Durham, North Carolina, a city in N ...

, and

Northumberland Northumberland () is a county in Northern England, one of two counties in England which border with Scotland. Notable landmarks in the county include Alnwick Castle, Bamburgh Castle, Hadrian's Wall and Hexham Abbey. It is bordered by land ...

who were killed in action during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

, designed by R. Atkinson, and installed in

York Minster The Cathedral and Metropolitical Church of Saint Peter in York, commonly known as York Minster, is the cathedral of York, North Yorkshire, England, and is one of the largest of its kind in Northern Europe. The minster is the seat of the Arch ...

in 1955.

History

The clock was first conceived in 1944 and designed by Robert d'Escourt Atkinson, chief assistant at the Royal Greenwich Observatory. Atkinson based the design on the appearance of the sun and stars from the viewpoint of a pilot flying over York. The mechanism and two dials were constructed by A.C.S. Westcott and Royal Greenwich Observatory craftsmen, and installed in the north transept of

in 1955. Damage to the clock's mechanism was sustained during a fire, on 9 July 1984; after 10 years' work attempting repair,

verger A verger (or virger, so called after the staff of the office, or wandsman (British)) is a person, usually a layperson, who assists in the ordering of religious services, particularly in Anglican churches. Etymology The title of ''verger'' ...

s ceased winding it, owing to its inaccuracies of time-keeping.

Display dials

The front dial shows the locations of the Sun and certain navigational stars as would be seen by a pilot flying south above York Minster. To locate his position, a fixed circular plate, about 62 cm (slightly over 2

feet The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...

) in diameter and slightly dished, carries a ground plan of the Minster and surrounding markings representative of city walls, rivers, and principal roads. Since the edge of the plate represents the effective horizon, its centre identifies the pilot's

nadir The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direc ...

. Mounted behind the plate there is a star-

planisphere In astronomy, a planisphere () is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist ...

, based on a north pole stereographic zenithal projection (a projection from the

north pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...

onto a plane passing through the

south pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...

, and perpendicular to the solar axis). This rotates once in a

sidereal day Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coor ...

on an axis passing through its south celestial pole and located some 13 cm above the centre of the horizon plate. For decoration it carries a few basic star patterns (considerably distorted owing to the projection used) and an eccentric

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The pat ...

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...

/ calendar ring faced with silver, and restricted in width to the distance between the solstitial points. Associated with the ring is a rayed apparent-sun emblem whose supporting arm system moves to and fro relative to a main mean-motion arm by an amount corresponding to the

equation of time In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in F ...

, and also radially to represent changes in the sun's declination. Sun-emblem and horizon-plate therefore combine to show the times of the Sun's rising, southing, and setting throughout the year and, by means of the rays of the sun emblem, the extent of the twilight. To complete the front dial display, two sets of curved wires are mounted in front of the planisphere. One set of two wires indicates lines of equal altitude 36° and 59.5° and supplements the edge of the horizon plate (altitude 0°); they cross a vertical north–south wire to indicate the Sun's meridian altitude at the equinoxes and solstices respectively. The second set, in addition to the north–south element, forms a complete circle and the sectors of two larger circles; all four wires intersect at the centre of the horizon plate (nadir) and a point near the top of the north–south line (zenith). The rear

, similar in size to the one in the front but strictly circular, displays the brightest stars of the main circumpolar constellations (

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

Ursa Minor Ursa Minor (Latin: 'Lesser Bear', contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, ...

, and Cassiopeia). It is centred on the north celestial pole and, with its encircling silvered ring of 24 hour intervals, rotates once a sidereal day relative to a fixed meridian-index.

Gearing

The

is attached to a large wheel driven by a

worm gear A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminol ...

, which is connected to a gear box containing the wheel-train. The gear wheels have ratios , , and , producing a solar to sidereal ratio of = : This produces an approximation for the

mean tropical year A tropical year or solar year (or tropical period) is the time that the Sun takes to return to the same position in the sky of a celestial body of the Solar System such as the Earth, completing a full cycle of seasons; for example, the time f ...

of 365.24219447 days (compare to 365.24219265 days). The worm gear serving the similar wheel of the mean-sun arm is connected to the input end of the gear box, and also, through a 3000:1 reduction gear, to a 1500 synchronous electric motor, running off the main electricity supply. For the equation correction, a wheel on a lever associated with the mean solar arm rolls round an annular cam of sheet brass about 61 cm in diameter. Beneath the planisphere, three small dials show hours, minutes, and seconds of

Greenwich Mean Time Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a con ...

, and three similar and balancing dials give local sidereal time in degrees, minutes, and seconds of arc. An aperture indicates the name of the day of the week.

References

{{Astronomical clocks Astronomical clocks in the United Kingdom

Astronomical clock An astronomical clock, horologium, or orloj is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the Sun, Moon, zodiacal constellations, and sometimes major planets. Definition ...

Individual clocks in England Buildings and structures completed in 1955 World War II memorials in England 1955 establishments in the United Kingdom