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Cardinal Direction
The four cardinal directions or cardinal points are the directions north, east, south, and west, commonly denoted by their initials N, E, S, and W. East
East
and west are at right angles to north and south, with east being in the clockwise direction of rotation from north and west being directly opposite east. Points between the cardinal directions form the points of the compass. The intermediate (intercardinal or ordinal) directions are northeast (NE), southeast (SE), southwest (SW), and northwest (NW)
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Octans
Octans
Octans
/ˈɒktænz/ is a faint constellation located in the deep southern sky. Its name is Latin
Latin
for the eighth part of a circle, but it is named after the octant, a navigational instrument. The constellation was devised by French astronomer Nicolas Louis de Lacaille in 1752, and it remains one of the 88 modern constellations.Contents1 History and mythology 2 Notable features2.1 Stars3 Namesakes 4 References 5 External linksHistory and mythology[edit] Octans
Octans
was one of 14 constellations created by Nicolas Louis de Lacaille during his expedition to the Cape of Good Hope, and was originally named "l’ Octans
Octans
de Reflexion", French for “the reflecting octant”. It was part of his catalogue of the southern sky, the Coelum Australe Stelliferum, which was published posthumously in 1763
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Arc (geometry)
In Euclidean geometry, an arc (symbol: ⌒) is a closed segment of a differentiable curve. A common example in the plane (a two-dimensional manifold), is a segment of a circle called a circular arc. In space, if the arc is part of a great circle (or great ellipse), it is called a great arc. Every pair of distinct points on a circle determines two arcs
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Equation Of Time
The equation of time describes the discrepancy between two kinds of solar time. The word equation is used in the medieval sense of "reconcile a difference". 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
Sun
with noons 24 hours apart. Apparent solar time
Apparent solar time
can be obtained by measurement of the current position (hour angle) of the Sun, as indicated (with limited accuracy) by a sundial. Mean
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 resolve to zero.[1] The equation of time is the east or west component of the analemma, a curve representing the angular offset of the Sun
Sun
from its mean position on the celestial sphere as viewed from Earth
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Azimuth
An azimuth (/ˈæzɪməθ/ ( listen)) (from the pl. form of the Arabic noun "السَّمْت" as-samt, meaning "the direction") is an angular measurement in a spherical coordinate system. The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth. An example of azimuth is the angular direction of a star in the sky. The star is the point of interest, the reference plane is the local horizontal area (e.g. a circular area 5 km in radius around an observer at sea level), and the reference vector points north. The azimuth is the angle between the north vector and the star's vector on the horizontal plane.[1] Azimuth
Azimuth
is usually measured in degrees (°)
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Astronomy
Astronomy
Astronomy
(from Greek: ἀστρονομία) is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets; the phenomena include supernova explosions, gamma ray bursts, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere
Earth's atmosphere
are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe
Universe
as a whole.[1] Astronomy
Astronomy
is one of the oldest of the natural sciences
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Celestial Sphere
In astronomy and navigation, the celestial sphere is an abstract sphere, with an arbitrarily large radius, that is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location. The celestial sphere is a practical tool for spherical astronomy, allowing astronomers to specify the apparent positions of objects in the sky if their distances are unknown or irrelevant.Contents1 Introduction 2 Celestial coordinate systems 3 History 4 Star globe 5 Bodies other than Earth 6 See also 7 Notes 8 References 9 External linksIntroduction[edit]Celestial Sphere, 18th century. Brooklyn Museum.Because astronomical objects are at such remote distances, casual observation of the sky offers no information on their actual distances
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Celestial Pole
The north and south celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to an observer at the Earth's North Pole
North Pole
and South Pole, respectively. As the Earth
Earth
spins on its axis, the two celestial poles remain fixed in the sky, and all other points appear to rotate around them, completing one circuit per day (strictly, per sidereal day). The celestial poles are also the poles of the celestial equatorial coordinate system, meaning they have declinations of +90 degrees and −90 degrees (for the north and south celestial poles, respectively). The celestial poles do not remain permanently fixed against the background of the stars
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Long Exposure Photography
Long-exposure, time-exposure, or slow-shutter photography involves using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements. Long-exposure photography
Long-exposure photography
captures one element that conventional photography does not: an extended period of time. The paths of bright moving objects become clearly visible. Clouds form broad bands, head and tail lights of cars draw bright streaks, stars leave trails in the sky, and water waves appear smoothened. Only bright objects will leave visible trails, whereas dark objects usually disappear. Boats in long exposures will disappear during daytime, but will draw bright trails from their lights at night.Contents1 Technique1.1 Night photography 1.2 Light painting 1.3 Water and long exposure2 Solargraphy 3 References 4 External linksTechnique[edit]A long exposure photo of a watch in the dark
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Shutter (photography)
In photography, a shutter is a device that allows light to pass for a determined period, exposing photographic film or a light-sensitive electronic sensor to light in order to capture a permanent image of a scene. A shutter can also be used to allow pulses of light to pass outwards, as seen in a movie projector or a signal lamp. A shutter of variable speed is used to control exposure time of the film. The shutter is so constructed that it automatically closes after a certain required time interval
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Darkness
Darkness, the polar opposite to brightness, is understood as a lack of illumination or an absence of visible light. Humans are unable to distinguish color in conditions of either high brightness or darkness.[1] In conditions of insufficient light, perception is achromatic and ultimately, black. The emotional response to darkness has generated metaphorical usages of the term in many cultures. Complete darkness
Complete darkness
is when the sun is more than 18 degrees below the horizon.Contents1 Scientific1.1 Perception 1.2 Physics 1.3 Technical2 Cultural2.1 Artistic 2.2 Literature2.2.1 Religion 2.2.2 Philosophy 2.2.3 Poetry 2.2.4 Language2.3 Greek mythology3 See also 4 References 5 External linksScientific[edit] Perception[edit]Stare at the image for a minute, then look away. The image of Jesus in inverted color will appear.The perception of darkness differs from the mere absence of light due to the effects of after images on perception
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Photograph
A photograph or photo is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic medium such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of what the human eye would see. The process and practice of creating photographs is called photography
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Concentric
In geometry, two or more objects are said to be concentric, coaxal, or coaxial when they share the same center or axis. Circles,[1] regular polygons[2] and regular polyhedra,[3] and spheres[4] may be concentric to one another (sharing the same center point), as may cylinders[5] (sharing the same central axis).Contents1 Geometric properties 2 Applications and examples 3 See also 4 References 5 External linksGeometric properties[edit] In the Euclidean plane, two circles that are concentric necessarily have different radii from each other.[6] However, circles in three-dimensional space may be concentric, and have the same radius as each other, but nevertheless be different circles. For example, two different meridians of a terrestrial globe are concentric with each other and with the globe of the earth (approximated as a sphere)
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Centre (geometry)
In geometry, a centre (or center) (from Greek κέντρον) of an object is a point in some sense in the middle of the object. According to the specific definition of centre taken into consideration, an object might have no centre. If geometry is regarded as the study of isometry groups then a centre is a fixed point of all the isometries which move the object onto itself.Contents1 Circles, spheres, and segments 2 Symmetric objects 3 Triangles 4 Tangential polygons and cyclic polygons 5 General polygons 6 See also 7 ReferencesCircles, spheres, and segments[edit] The centre of a circle is the point equidistant from the points on the edge. Similarly the centre of a sphere is the point equidistant from the points on the surface, and the centre of a line segment is the midpoint of the two ends. Symmetric objects[edit] For objects with several symmetries, the centre of symmetry is the point left unchanged by the symmetric actions
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Daylight Saving Time
Daylight saving time
Daylight saving time
(abbreviated DST), sometimes referred to as daylight savings time in US, Canadian and Australian speech,[1][2] and known as British Summer Time
British Summer Time
(BST) in the UK and just summer time in some countries, is the practice of advancing clocks during summer months so that evening daylight lasts longer, while sacrificing normal sunrise times. Typically, regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time.[3] George Hudson proposed the idea of daylight saving in 1895.[4] The German Empire
German Empire
and Austria-Hungary
Austria-Hungary
organized the first nationwide implementation, starting on April 30, 1916
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Degree (angle)
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit
SI unit
of angular measure is the radian, but it is mentioned in the SI brochure as an accepted unit.[4] Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians.Contents1 History 2 Subdivisions 3 Alternative units 4 See also 5 Notes 6 References 7 External linksHistory[edit] See also: DecansA circle with an equilateral chord (red). One sixtieth of this arc is a degree. Six such chords complete the circle.The original motivation for choosing the degree as a unit of rotations and angles is unknown
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