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Sundials
A sundial is a horology, horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the position of the Sun, apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate (the ''dial'') and a gnomon, which casts a shadow onto the dial. As the Sun diurnal motion, appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The ''style'' is the time-telling edge of the gnomon, though a single point or ''nodus'' may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be polar alignment, parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude. The term ''sundial'' can r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equation Of Time
The equation of time describes the discrepancy between two kinds of solar time. The two times that differ are the apparent solar time, which directly tracks the diurnal motion of the Sun, and mean solar time, which tracks a theoretical mean Sun with uniform motion along the celestial equator. Apparent solar time can be obtained by measurement of the current position (Hour angle#Solar hour angle, hour angle) of the Sun, as indicated (with limited accuracy) by a sundial. ''Mean'' solar time, for the same place, would be the time indicated by a steady clock set so that over the year its differences from apparent solar time would have a mean of zero. The equation of time is the east or west component of the analemma, a curve representing the angular offset of the Sun from its mean position on the celestial sphere as viewed from Earth. The equation of time values for each day of the year, compiled by astronomical observatory, observatories, were widely listed in almanacs and ephemeri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Analemmatic Sundial
Analemmatic sundials are a type of horizontal sundial that has a vertical gnomon and hour markers positioned in an elliptical pattern. The gnomon is not fixed and must change position daily to accurately indicate time of day. The time of day is read by the position of the shadow on the ellipse."Analemmatic sundials: How to build one and why they work" C.J. Budd and C.J. Sangwin, maths.org, 1 June 2000 Like most sundials, analemmatic sundials mark rather than clock time. Description An analemmatic sundial is completely defined by: * The size of its ellipse (chosen by the designer). * The |
Gnomon
A gnomon (; ) is the part of a sundial that casts a shadow. The term is used for a variety of purposes in mathematics and other fields, typically to measure directions, position, or time. History A painted stick dating from 2300 BC that was excavated at the archeological site of Taosi is the oldest gnomon known in China. The gnomon was widely used in ancient China from the second millennium BC onward in order to determine the changes in seasons, orientation, and geographical latitude. The ancient Chinese used shadow measurements for creating calendars that are mentioned in several ancient texts. According to the collection of Zhou Chinese poetic anthologies ''Classic of Poetry'', one of the distant ancestors of King Wen of the Zhou dynasty used to measure gnomon shadow lengths to determine the orientation around the 14th century BC. The ancient Greek philosopher Anaximander (610–546 BC) is credited with introducing this Babylonian instrument to the Ancient Greeks. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Daylight Saving Time
Daylight saving time (DST), also referred to as daylight savings time, daylight time (Daylight saving time in the United States, United States and Daylight saving time in Canada, Canada), or summer time (British Summer Time, United Kingdom, Summer time in Europe, European Union, and others), is the practice of advancing clocks to make better use of the longer daylight available during summer so that darkness falls at a later clock time. The standard implementation of DST is to set clocks forward by one hour in spring (season), spring or late winter, and to set clocks back by one hour to standard time in the autumn (or ''fall'' in North American English, hence the mnemonic: "spring forward and fall back"). Overview As of 2023, around 34 percent of the world's countries use DST. Some countries observe it only in some regions. In Canada, all of Yukon Time Zone, Yukon, most of Time in Saskatchewan, Saskatchewan, and parts of Nunavut, Ontario, British Columbia and Quebec do not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Time
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based on astronomical observations: #Apparent solar time, apparent solar time and #Mean solar time, mean solar time (discussed in this article), and ''sidereal time'', which is based on the apparent motions of stars other than the Sun. Introduction A tall pole vertically fixed in the ground casts a shadow on any sunny day. At one moment during the day, the shadow will point exactly north or south (or disappear when and if the Sun moves directly overhead). That instant is called solar noon, ''local apparent noon'', or 12:00 local apparent time. About 24 hours later the shadow will again point north–south, the Sun seeming to have covered a 360-degree arc around Earth's axis. When the Sun has covered exactly 15 degrees (1/24 of a circle, both a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the center (geometry), ''center'' of the sphere, and the distance is the sphere's ''radius''. The earliest known mentions of spheres appear in the work of the Greek mathematics, ancient Greek mathematicians. The sphere is a fundamental surface in many fields of mathematics. Spheres and nearly-spherical shapes also appear in nature and industry. Bubble (physics), Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is spherical Earth, often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres rolling, roll smoothly in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oculus (architecture)
An oculus (; ) is a circular opening in the center of a dome or in a wall. Originating in classical architecture, it is a feature of Byzantine architecture, Byzantine and Neoclassical architecture. A horizontal oculus in the center of a dome is also called opaion (; ). Oeil-de-boeuf An ''oeil-de-boeuf'' (; ), also ''œil de bœuf'' and sometimes anglicized as ''ox-eye window'', is a relatively small ellipse, elliptical window, typically for an upper storey, and sometimes set in a roof slope as a dormer, or above a door to let in Daylighting (architecture), natural light. These are relatively small windows, traditionally oval. The term is increasingly used for circular windows (in which case it could also be called an oculus), but not for holes in domes or ceilings. Windows of this type are commonly found in the grand architecture of baroque architecture, Baroque France. The term is also applied to similar round windows, such as those found in Georgian architecture in Great B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equatorial Sundial Topview
Equatorial may refer to something related to: *Earth's equator **the tropics, the Earth's equatorial region **tropical climate *the Celestial equator **equatorial orbit **equatorial coordinate system **equatorial mount An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, called ''polar axis'', parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescope mount, tel ..., of telescopes * equatorial bond, a type of chemical bond orientation See also * * Equator (other) {{Disambiguation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Greenwich
Greenwich ( , , ) is an List of areas of London, area in south-east London, England, within the Ceremonial counties of England, ceremonial county of Greater London, east-south-east of Charing Cross. Greenwich is notable for its maritime history and for giving its name to the Prime meridian (Greenwich), Greenwich Meridian (0° longitude) and Greenwich Mean Time. The town became the site of a royal palace, the Palace of Placentia, from the 15th century and was the birthplace of many House of Tudor, Tudors, including Henry VIII of England, Henry VIII and Elizabeth I. The palace fell into disrepair during the English Civil War and was demolished, eventually being replaced by the Greenwich Hospital (London), Royal Naval Hospital for Sailors, designed by Sir Christopher Wren and his assistant Nicholas Hawksmoor. These buildings became the Old Royal Naval College, Royal Naval College in 1873, and they remained a military education establishment until 1998, when they passed into the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Longitude
Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west. Because of the Earth's rotation, there is a close connection between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
True North
True north is the direction along Earth's surface towards the place where the imaginary rotational axis of the Earth intersects the surface of the Earth on its Northern Hemisphere, northern half, the True North Pole. True south is the direction opposite to the true north. It is important to make the distinction from ''magnetic'' north, which points towards North magnetic pole, an ever changing location close to the True North Pole determined Earth's magnetic field. Due to fundamental limitations in map projection, true north also differs from the grid north which is marked by the direction of the grid lines on a typical printed map. However, the geographic coordinate system, longitude lines on a globe lead to the true poles, because the three-dimensional representation avoids those limitations. The celestial pole is the location on the imaginary celestial sphere where an imaginary extension of the rotational axis of the Earth intersects the celestial sphere. Within a margin of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
