sundial

enUK

sun·di·al

S0886600 (sŭn′dī′əl, -dīl′)n. An instrument that indicates local apparent solar time by the shadow cast by a central projecting pointer on a surrounding calibrated dial.

sundial

(ˈsʌnˌdaɪəl) n (Horology) a device indicating the time during the hours of sunlight by means of a stationary arm (the gnomon) that casts a shadow onto a plate or surface marked in hours

sun•di•al

(ˈsʌnˌdaɪ əl, -ˌdaɪl)

n. an instrument that indicates the time of day by means of the position, on a graduated plate or surface, of the shadow of the gnomon as cast by the sun. [1570–80]

Thesaurus

Noun

sundial - timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dialgnomon - indicator provided by the stationary arm whose shadow indicates the time on the sundialhorologe, timepiece, timekeeper - a measuring instrument or device for keeping time

Translations

日昝

sun

(san) noun1. the round body in the sky that gives light and heat to the earth. The Sun is nearly 150 million kilometres away from the Earth.太阳2. any of the fixed stars. Do other suns have planets revolving round them?恒星3. light and heat from the sun; sunshine. We sat in the sun; In Britain they don't get enough sun; The sun has faded the curtains.日光 verb – past tense, past participle sunned – to expose (oneself) to the sun's rays. He's sunning himself in the garden.晒太阳ˈsunless adjective without sun, or lacking sunlight. a sunless room.无日光的ˈsunny adjective1. filled with sunshine. sunny weather.和煦的2. cheerful and happy. The child has a sunny nature.快乐的ˈsunniness noun 欢乐，和煦 ˈsunbathe verb to lie or sit in the sun, especially wearing few clothes, in order to get a suntan. 日光浴ˈsunbeam noun a ray of the sun. 一道阳光ˈsunburn noun the brown or red colour of the skin caused by exposure to the sun's rays. 晒伤ˈsunburned, ˈsunburnt adjectivesunburnt faces.晒伤的ˈsundial noun a device, usually in a garden, for telling time from the shadow of a rod or plate on its surface cast by the sun. 日昝ˈsundown noun (especially American) sunset. 日落ˈsunflower noun a type of large yellow flower with petals like rays of the sun, from whose seeds we get oil. 向日葵ˈsunglasses noun plural glasses of dark-coloured glass or plastic to protect the eyes in bright sunlight. 太阳眼镜ˈsunlight noun the light of the sun. The cat was sitting in a patch of sunlight.阳光ˈsunlit adjective lighted up by the sun. a sunlit room.阳光照射的ˈsunrise noun the rising of the sun in the morning, or the time of this. 日出ˈsunset noun the setting of the sun, or the time of this. the red glow of the sunset.日落ˈsunshade noun a type of umbrella for sheltering a person from the sun; a parasol. 遮阳伞ˈsunshine noun1. the light of the sun. The children were playing in the sunshine.阳光2. cheerfulness or happiness. 快乐ˈsunstroke noun a serious illness caused by being in very hot sunshine for too long. 日射病，中暑 ˈsuntan noun a brown colour of the skin caused by exposure to the sun. I'm trying to get a suntan.晒黑catch the sun to become sunburnt. 晒黑的under the sun in the whole world. I'm sure that he must have visited every country under the sun. 在世界上，天下

sundial

enUK

sundial,

instrument that indicates the time of day by the shadow, cast on a surface marked to show hours or fractions of hours, of an object on which the sun's rays fall. Although any object whose shadow is used to determine time is called a gnomon, the term is usually applied to a style, pin, metal plate, or other shadow-casting object that is an integral part of a sundial. Forerunners of the sundial include poles or upright stones used as gnomons; pyramids and obelisks were so used in Egypt. Both stationary and portable sundials were probably developed in Egypt or in Mesopotamia. The earliest extant sundial, an Egyptian instrument of c.1500 B.C., is a flat stone on which is fixed an L-shaped bar whose short vertical limb casts a shadow measured by markings on the longer horizontal limb. The sundial was greatly improved (c.1st cent. A.D.) by setting the gnomon parallel to the earth's axis of rotation so that the apparent east-to-west motion of the sun governs the swing of the shadow. The development of trigonometry permitted precise calculations for the marking of dials and stimulated the advance of gnomonics (dial marking). Although watches and clocks came into popular use in the 18th cent., sundials were long employed for setting and checking them. The heliochronometer, a highly accurate instrument in which the shadow is cast by a fine wire, was used until c.1900 to set the watches of French railwaymen. Solar (or apparent) time indicated by sundials and clock (or mean) time are different and must be correlated by the use of tables showing daily variations in sun time. A correction must also be made for the difference in longitude between the position of a sundial and the standard time meridian of a given locality. Although sundials are still used in many areas, including Japan and China, they are regarded today chiefly as adornments. The largest sundial in the world, constructed c.1724 in Jaipur, India, covers almost one acre (.4 hectare) and has a gnomon over 100 ft (30 m) high surmounted by an observatory. Notable collections of sundials are at the Adler Planetarium, the Metropolitan Museum of Art, and the Harvard College Observatory.

Bibliography

See F. W. Cousins, Sundials (1969); R. R. J. Rohr, Sundials (tr. 1970).

Sundial

an instrument for telling time by the sun. A sundial consists of a gnomon, which may be a rod or triangular plate, and a graduated plate on which the gnomon casts a shadow. The place on the dial plate where the shadow falls indicates the apparent solar time. Three types of sundials are distinguished according to the position of the dial plate: equatorial, horizontal, and vertical. In all three types, the rod or the edge of the gnomon is made parallel to the earth’s axis and intersects the dial plate at the dial’s “center,” which is the point from which the hour lines radiate. The line corresponding to noon is located in the plane of the meridian passing through this center.

In equatorial sundials, the plane of the dial plate is parallel to the plane of the celestial equator. The dial plate is calibrated with equally spaced graduations on the basis of 360° being equal to 24 hours.

In horizontal sundials, the dial plate is horizontal and is calibrated in accordance with the equation

tan x = (tan t)(sin φ)

where x is the angle formed at the center of the dial by the given hour line and the noon line, t is the hour angle of the sun (the apparent solar time), and φ is the geographic latitude of the place where the dial is located. The hour lines for6 A.M. and 6 P.M. are always perpendicular to the noon line.

Vertical sundials are usually found on the walls of various structures. Consequently, the plane of the dial plate may have any azimuth. In such sundials, the hour lines are symmetric with respect to the noon line only when the dial plate is perpendicular to the meridian. In this case, the equation for the calibration of the dial has the form

tan x = (tan t)(cos φ)

Various types of portable sundials are also known.

The position of the shadow on the dial plate indicates the apparent solar time. To obtain the mean solar time, the equation of time must be added to the apparent solar time. Standard, or zone, time can be obtained by taking into account an additional correction that depends on the time zone and the geographic longitude of the place where the sundial is located. The accuracy of sundial readings is generally not better than several minutes.

sundial

[′sən‚dīl] (horology) An instrument for telling time by the sun; it is composed of a stylus that casts a shadow and a dial plate, on which hour lines are marked and upon which the shadow falls.

sundial

sun·di·al

sundial

sun•di•al

sun

sundial

sundial,

Bibliography

Sundial

sundial

SUNDIAL

sundial

Words related to sundial

noun timepiece that indicates the daylight hours by the shadow that the gnomon casts on a calibrated dial

Related Words