1.
Plymouth Sound
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Plymouth Sound, or locally just The Sound, is a bay on the English Channel at Plymouth in England. Its southwest and southeast corners are Penlee Point in Cornwall and Wembury Point in Devon and its northern limit is Plymouth Hoe giving a north-south distance of nearly 3 nautical miles. The Sound has three water entrances, the marine entrance is from the English Channel to the south, with a deep-water channel to the west of the Plymouth Breakwater. There are two inlets, one, from the northwest, is from the River Tamar via the Hamoaze and Devonport Dockyard. The other, at northeast, is from the River Plym disgorging into its narrow estuary, in addition to ships of the Royal Navy, large commercial vessels, including ferries to France and Spain use the Sound from Millbay Docks. Fishing vessels use it from Sutton Harbour beside the old town of Plymouth, there are marinas at Sutton Harbour, Mount Wise in the Hamoaze and at Turnchapel. Waterborne traffic in the Sound is controlled by the Queens Harbour Master for Plymouth, in the centre of the Sound, midway between Bovisand Bay and Cawsand Bay, is Plymouth Breakwater, which creates a harbour protecting anchored ships from the frequent south-western storms. The breakwater is around 1,700 yards long, stands in around 11 metres /36 feet of water and was built by John Rennie, the breakwater has a 23-metre-tall lighthouse on its western end and a 9-metre-tall beacon with a spherical cage on top at the eastern end. It is said that the cage is a device designed to keep wrecked sailors from drowning in the huge waves of a storm on the low-lying breakwater. Drakes Island is 400 metres long and around 100 metres wide and it was fortified to defend Drakes Channel, the only deep-water route to Devonport. The Bridge is a reef that links Drakes Island and the Cornish mainland. At low water the depth of the Bridge can be less than one metre, in World War I this natural barrier was supplemented by other obstructions to prevent submarines and small ships attacking the naval base. Mount Batten, a former Royal Air Force flying boat and search, T. E. Lawrence was stationed here as Aircraftman Shaw. Over the years, the Sound has been defended by Drakes Island, Picklecombe Fort, Cawsand Fort, a harbour and reservoir were built at Bovisand before the fort existed to supply men-o-war anchored in the Sound with fresh water. Joseph Whidbey supervised the building of the Breakwater from Bovisand Lodge, the Titanic was supposed to have docked here briefly on its return voyage to Britain, and the ship had a painting of Plymouth sound on board. This event caused a local and national sensation as thousands took to the water, several paintings in Londons National Maritime Museum document the event, such as the one shown here. The Sound has been the site of a number of crashes and shipwrecks, Die Fraumetta Catharina von Flensburg. The P&O ship Nepaul sank on the Shagstone in December 1890, a Short Sunderland flying boat crashed in March 1942 between the Breakwater Fort and the breakwater lighthouse killing five passengers
2.
United Kingdom
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The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom or Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain, Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state—the Republic of Ireland. The Irish Sea lies between Great Britain and Ireland, with an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world and the 11th-largest in Europe. It is also the 21st-most populous country, with an estimated 65.1 million inhabitants, together, this makes it the fourth-most densely populated country in the European Union. The United Kingdom is a monarchy with a parliamentary system of governance. The monarch is Queen Elizabeth II, who has reigned since 6 February 1952, other major urban areas in the United Kingdom include the regions of Birmingham, Leeds, Glasgow, Liverpool and Manchester. The United Kingdom consists of four countries—England, Scotland, Wales, the last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively. The relationships among the countries of the UK have changed over time, Wales was annexed by the Kingdom of England under the Laws in Wales Acts 1535 and 1542. A treaty between England and Scotland resulted in 1707 in a unified Kingdom of Great Britain, which merged in 1801 with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland. Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain, there are fourteen British Overseas Territories. These are the remnants of the British Empire which, at its height in the 1920s, British influence can be observed in the language, culture and legal systems of many of its former colonies. The United Kingdom is a country and has the worlds fifth-largest economy by nominal GDP. The UK is considered to have an economy and is categorised as very high in the Human Development Index. It was the worlds first industrialised country and the worlds foremost power during the 19th, the UK remains a great power with considerable economic, cultural, military, scientific and political influence internationally. It is a nuclear weapons state and its military expenditure ranks fourth or fifth in the world. The UK has been a permanent member of the United Nations Security Council since its first session in 1946 and it has been a leading member state of the EU and its predecessor, the European Economic Community, since 1973. However, on 23 June 2016, a referendum on the UKs membership of the EU resulted in a decision to leave. The Acts of Union 1800 united the Kingdom of Great Britain, Scotland, Wales and Northern Ireland have devolved self-government
3.
Atmospheric optics
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Atmospheric optics deals with how the unique optical properties of the Earths atmosphere cause a wide range of spectacular optical phenomena. The blue color of the sky is a result of Rayleigh scattering which redirects higher frequency sunlight back into the field of view of the observer. Because blue light is scattered more easily than red light, the sun takes on a reddish hue when it is observed through a thick atmosphere, additional particulate matter in the sky can scatter different colors at different angles creating colorful glowing skies at dusk and dawn. Scattering off of ice crystals and other particles in the atmosphere are responsible for halos, afterglows, coronas, rays of sunlight, the variation in these kinds of phenomena is due to different particle sizes and geometries. Mirages are optical phenomena in which light rays are bent due to variations in the refraction index of air. Other optical phenomena associated with include the Novaya Zemlya effect where the sun appears to rise earlier or set later than predicted with a distorted shape. Rainbows are the result of a combination of reflection and dispersive refraction of light in raindrops. Because rainbows are seen on the side of the sky as the sun. He said that judging the distance of an object depends on there being a sequence of intervening bodies between the object and the observer. With the Moon, however, there are no intervening objects, therefore, since the size of an object depends on its observed distance, which is in this case inaccurate, the Moon appears larger on the horizon. For over 100 years, research on the Moon illusion has been conducted by scientists who invariably have been psychologists specializing in human perception. After reviewing the different explanations in their 2002 book The Mystery of the Moon Illusion, Ross. Light from the sky is a result of the scattering of sunlight, on a sunny day Rayleigh scattering gives the sky a blue gradient — dark in the zenith, light near the horizon. Light that comes in from overhead encounters 1/38th of the air mass that light coming along a horizon path encounters, so, fewer particles scatter the zenith sunbeam, and therefore the light remains a darker blue. The blueness is at the horizon because the light coming from great distances is also preferentially scattered. This results in a red shift of the far lightsources that is compensated by the hue of the scattered light in the line of sight. In other words, the red light scatters also, if it does so at a point a distance from the observer it has a much higher chance of reaching the observer than blue light. At distances nearing infinity the light is therefore white
4.
Ray (optics)
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In optics a ray is an idealized model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow. This allows even very complex systems to be analyzed mathematically or simulated by computer. Ray theory does not describe phenomena such as interference and diffraction, a light ray is a line that is perpendicular to the lights wavefronts, its tangent is collinear with the wave vector. Light rays in homogeneous media are straight and they bend at the interface between two dissimilar media and may be curved in a medium in which the refractive index changes. Geometric optics describes how rays propagate through an optical system, objects to be imaged are treated as collections of independent point sources, each producing spherical wavefronts and corresponding outward rays. Rays from each point can be mathematically propagated to locate the corresponding point on the image. There are many special rays that are used in modelling to analyze an optical system. These are defined and described below, grouped by the type of system they are used to model, an incident ray is a ray of light that strikes a surface. The angle between this ray and the perpendicular or normal to the surface is the angle of incidence, the reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the normal and the reflected ray is known as the angle of reflection. The Law of Reflection says that for a surface, the angle of reflection always equals the angle of incidence. The refracted ray or transmitted ray corresponding to an incident ray represents the light that is transmitted through the surface. The angle between this ray and the normal is known as the angle of refraction, and it is given by Snells Law. Conservation of energy requires that the power in the incident ray must equal the sum of the power in the ray, the power in the reflected ray. If the material is birefringent, the ray may split into ordinary and extraordinary rays. A meridional ray or tangential ray is a ray that is confined to the containing the systems optical axis. A skew ray is a ray that does not propagate in a plane that contains both the point and the optical axis. Such rays do not cross the optical axis anywhere, and are not parallel to it
5.
Sunlight
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Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earths atmosphere, and is obvious as daylight when the Sun is above the horizon, when the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, the World Meteorological Organization uses the term sunshine duration to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an Average over the earth of 164 Watts per square meter over a 24 hour day. The ultraviolet radiation in sunlight has both positive and negative effects, as it is both a principal source of vitamin D3 and a mutagen. Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface. Researchers may record sunlight using a sunshine recorder, pyranometer, or pyrheliometer, to calculate the amount of sunlight reaching the ground, both Earths elliptical orbit and the attenuation by Earths atmosphere have to be taken into account. In this formula dn–3 is used, because in modern times Earths perihelion, the closest approach to the Sun and, therefore, the value of 0.033412 is determined knowing that the ratio between the perihelion squared and the aphelion squared should be approximately 0.935338. The solar illuminance constant, is equal to 128×103 lx, the atmospheric extinction brings the number of lux down to around 100000. The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and it is about 3. 3% higher than average in January and 3. 3% lower in July. In terms of energy, sunlight at Earths surface is around 52 to 55 percent infrared,42 to 43 percent visible, and 3 to 5 percent ultraviolet. At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet, direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. This is higher than the efficacy of most artificial lighting, which means using sunlight for illumination heats up a less than using most forms of artificial lighting. Multiplying the figure of 1050 watts per square metre by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98000 lux on a surface at sea level. The illumination of a surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole, dividing the irradiance of 1050 W/m2 by the size of the suns disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. Multiplying this by π gives a limit to the irradiance which can be focused on a surface using mirrors,48.5 MW/m2
6.
Stratocumulus cloud
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Weak convective currents create shallow cloud layers because of drier, stable air above preventing continued vertical development. Most often, stratocumulus produce no precipitation, and when they do, however, these clouds are often seen at either the front or tail end of worse weather, so they may indicate storms to come, in the form of thunderheads or gusty winds. Stratocumulus clouds are same in appearance to altocumulus and are mistaken for such. This often does not apply when stratocumulus is of a broken, fractus form, stratocumulus is also often, though not always, darker in colour than altocumulus. Stratocumulus clouds are the type of cloud that can produce crepuscular rays. Thin stratocumulus clouds are often the cause of corona effects around the Moon at night. All stratocumulus subtypes are coded CL5 except when formed from free convective mother clouds or when formed separately from co-existing, stratocumulus Stratiformis are extensive flat but slightly lumpy sheets that show only minimal convective activity. Stratocumulus Lenticularis are separate flat elongated seed-shaped clouds and they are typical for polar countries or warmer climate during winter seasons. They also can be formed by winds passing hills or mountains, such as Foehn winds, stratocumulus Castellanus have stronger convective activity due to the presence of increasingly unstable air. They are distinct from other stratocumulus by puffy tower-like formations atop the cloud layer, stratocumulus castellanus may develop into cumulus congestus under auspicious conditions. Any showers from stratocumulus castellanus are not usually as heavy as those from cumulus congestus, stratocumulus Opacus is a dark layer of clouds covering entire sky without any break. However, the sheet is not completely uniform, so that separate cloud bases still can be seen. This is the main precipitating type, however any rain is usually light, if the cloud layer becomes grayer to the point when individual clouds can’t be distinguished, stratocumulus turn into stratus clouds. Stratocumulus Perlucidus is a layer of clouds with small spaces, appearing in irregular pattern. Stratocumulus Translucidus consist of groups of stratocumulus clouds, with a clear sky visible between them. Stratocumulus Undulatus clouds appear as nearly parallel waves, rolls or separate elongated clouds, stratocumulus Duplicatus clouds appear as stratocumulus clouds with two or more layers or sheets. Stratocumulus duplicatus is common on species lenticularis or lenticular cloud, stratocumulus Lacunosus clouds are very uncommon. They only occur there are localized downdrafts striking through the stratocumuliform cloud
7.
Perspectivity
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In geometry and in its applications to drawing, a perspectivity is the formation of an image in a picture plane of a scene viewed from a fixed point. The science of graphical perspective uses perspectivities to make images in proper proportion. According to Kirsti Andersen, the first author to describe perspectivity was Leon Alberti in his De Pictura. In English, Brook Taylor presented his Linear Perspective in 1715, the Lines producing that Projection, taken all together, are called the System of Rays. And when those Rays all pass thro’ one and same Point, a special symbol has been used to show that points X and Y are related by a perspectivity, X ⩞ Y. In this notation, to show that the center of perspectivity is P, using the language of functions, a central perspectivity with center P is a function f P, ↦ defined by f P = Y whenever P ∈ X Y. This map is an involution, that is, f P = X for all X ∈, the existence of a perspectivity means that corresponding points are in perspective. The dual concept, axial perspectivity, is the correspondence between the lines of two pencils determined by a projective range, the composition of two perspectivities is, in general, not a perspectivity. A perspectivity or a composition of two or more perspectivities is called a projectivity, theorem, Any projectivity from a projective range to itself can be written as the composition of three perspectivities. Theorem, A projectivity between two distinct ranges which fixes a point is a perspectivity. The bijective correspondence between points on two lines in a plane determined by a point of that plane not on either line has higher-dimensional analogues which will also be called perspectivities, let Sm and Tm be two distinct m-dimensional projective spaces contained in an n-dimensional projective space Rn. Let Pn−m−1 be a subspace of Rn with no points in common with either Sm or Tm. For each point X of Sm, the space L spanned by X and this correspondence fP is also called a perspectivity. The central perspectivity described above is the case with n =2 and m =1, let S2 and T2 be two distinct projective planes in a projective 3-space R3. This composition is a map of the points of S2 onto itself which preserves collinear points and is called a perspective collineation. Let φ be a perspective collineation of S2, each point of the line of intersection of S2 and T2 will be fixed by φ and this line is called the axis of φ. Let point P be the intersection of line OO* with the plane S2, P is also fixed by φ and every line of S2 that passes through P is stabilized by φ. P is called the center of φ, the restriction of φ to any line of S2 not passing through P is the central perspectivity in S2 with center P between that line and the line which is its image under φ. T
8.
Twilight
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Twilight is the illumination of the Earths lower atmosphere when the Sun itself is not directly visible because it is below the horizon. Twilight is produced by scattering in the upper atmosphere, illuminating the lower atmosphere so that the surface of the Earth is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs, the further the Sun is below the horizon, the dimmer the twilight. When the Sun reaches 18 degrees below the horizon, the brightness is nearly zero. When the Sun again reaches 18 degrees below the horizon, nighttime becomes morning twilight, Twilight should not be confused with auroras, which can have a similar appearance in the night sky at high latitudes. By analogy with evening twilight, the word twilight is also used metaphorically, to imply that something is losing strength. For example, very old people may be said to be in the twilight of their lives, the collateral adjective for twilight is crepuscular which is sometimes applied to insects, fish, and mammals that are most active during that time. Twilight is defined according to the elevation angle θs, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight. Morning civil twilight begins when the center of the sun is 6° below the horizon. Evening civil twilight begins at sunset or when the center of the sun is 0°50′ below the horizon. In the United States military, the initialisms BMCT and EECT are used to refer to these periods, morning nautical twilight begins and evening nautical twilight ends when the geometric center of the sun reaches 12° below the horizon. Morning astronomical twilight begins and Evening astronomical twilight ends when the center of the Sun reaches 18° below the horizon. There are three established and widely accepted subcategories of twilight, civil twilight, nautical twilight, and astronomical twilight, under clear weather conditions, civil twilight approximates the limit at which solar illumination suffices for the human eye to clearly distinguish terrestrial objects. Enough sunlight renders artificial sources unnecessary for most outdoor activities, at civil dawn, the beginning of morning civil twilight, and at civil dusk, the end of evening civil twilight, sunlight clearly defines the horizon while the brightest stars and planets can appear. As observed from the Earth, sky-gazers know Venus, the brightest planet, law-makers have enshrined the concept of civil twilight. Such statutes typically use a period after sunset or before sunrise. The period may affect when pilots require a rating to fly aircraft
9.
Anticrepuscular rays
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Anticrepuscular rays or antisolar rays are similar to crepuscular rays, but seen opposite the sun in the sky. Anticrepuscular rays are near-parallel, but appear to converge at the point because of linear perspective. Anticrepuscular rays are most frequently visible near sunrise or sunset, crepuscular rays are usually much brighter than anticrepuscular rays. This is because for crepuscular rays, seen on the side of the sky as the sun. Although anticrepuscular rays appear to converge onto a point opposite the sun, the rays are in fact parallel, and their apparent convergence is to the vanishing point at infinity
10.
Florida
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Florida /ˈflɒrᵻdə/ is a state located in the southeastern region of the United States. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia, to the east by the Atlantic Ocean, Florida is the 22nd-most extensive, the 3rd-most populous, and the 8th-most densely populated of the U. S. states. Jacksonville is the most populous municipality in the state and is the largest city by area in the contiguous United States, the Miami metropolitan area is Floridas most populous urban area. The city of Tallahassee is the state capital, much of the state is at or near sea level and is characterized by sedimentary soil. The climate varies from subtropical in the north to tropical in the south, the American alligator, American crocodile, Florida panther, and manatee can be found in the Everglades National Park. It was a location of the Seminole Wars against the Native Americans. Today, Florida is distinctive for its large Cuban expatriate community and high population growth, the states economy relies mainly on tourism, agriculture, and transportation, which developed in the late 19th century. Florida is also renowned for amusement parks, orange crops, the Kennedy Space Center, Florida has attracted many writers such as Marjorie Kinnan Rawlings, Ernest Hemingway and Tennessee Williams, and continues to attract celebrities and athletes. It is internationally known for golf, tennis, auto racing, by the 16th century, the earliest time for which there is a historical record, major Native American groups included the Apalachee, the Timucua, the Ais, the Tocobaga, the Calusa and the Tequesta. Florida was the first part of the continental United States to be visited and settled by Europeans, the earliest known European explorers came with the Spanish conquistador Juan Ponce de León. Ponce de León spotted and landed on the peninsula on April 2,1513 and he named the region La Florida. The story that he was searching for the Fountain of Youth is a myth, in May 1539, Conquistador Hernando de Soto skirted the coast of Florida, searching for a deep harbor to land. He described seeing a wall of red mangroves spread mile after mile, some reaching as high as 70 feet. Very soon, many smokes appeared along the whole coast, billowing against the sky, the Spanish introduced Christianity, cattle, horses, sheep, the Spanish language, and more to Florida. Both the Spanish and French established settlements in Florida, with varying degrees of success, in 1559, Don Tristán de Luna y Arellano established a settlement at present-day Pensacola, making it the first attempted settlement in Florida, but it was abandoned by 1561. Spain maintained tenuous control over the region by converting the tribes to Christianity. The area of Spanish Florida diminished with the establishment of English settlements to the north, the English attacked St. Augustine, burning the city and its cathedral to the ground several times. Florida attracted numerous Africans and African-Americans from adjacent British colonies who sought freedom from slavery, in 1738, Governor Manuel de Montiano established Fort Gracia Real de Santa Teresa de Mose near St
11.
Antisolar point
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The antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun from the viewpoint of an observer. This means that the point lies above the horizon when the Sun is below it. On a sunny day, the point can be easily found. The antisolar point forms the center of several optical phenomena, including rainbows, glories. Occasionally, during sunset or sunrise, anticrepuscular rays can be seen to converge at the point near the horizon. This is an illusion, however, caused by perspective. In reality, the rays run parallel to each other, also, on a moonless night away from city lights, it is often possible to see the gegenschein at that point, arising from the back-scattering of light by interplanetary dust. In astronomy, when the moon or planets are in opposition, the anthelic point is often used as a synonym for the antisolar point, but the two should be differentiated. There are several phenomena that are centered on or converge on the anthelic point, such as the anthelion, Wegener arcs, Tricker arcs
12.
Rayleigh scattering
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Rayleigh scattering does not change the state of material and is, hence, a parametric process. The particles may be atoms or molecules. It can occur when light travels through transparent solids and liquids, Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, the particle therefore becomes a small radiating dipole whose radiation we see as scattered light. Rayleigh scattering of sunlight in the atmosphere causes diffuse sky radiation, which is the reason for the color of the sky. The amount of scattering is proportional to the fourth power of the wavelength. This can lead to changes in the state of the molecules. Furthermore, the contribution has the same wavelengths dependency as the elastic part. Scattering by particles similar to, or larger than, the wavelength of light is treated by the Mie theory. Rayleigh scattering applies to particles that are small with respect to wavelengths of light, on the other hand, anomalous diffraction theory applies to optically soft but larger particles. The size of a particle is often parameterized by the ratio where r is its characteristic length. The wavelength dependence is characteristic of dipole scattering and the volume dependence will apply to any scattering mechanism, objects with x ≫1 act as geometric shapes, scattering light according to their projected area. At the intermediate x ≃1 of Mie scattering, interference effects develop through phase variations over the objects surface, Rayleigh scattering applies to the case when the scattering particle is very small and the whole surface re-radiates with the same phase. For example, the constituent of the atmosphere, nitrogen, has a Rayleigh cross section of 5. 1×10−31 m2 at a wavelength of 532 nm. This means that at atmospheric pressure, where there are about 2×1025 molecules per cubic meter, the strong wavelength dependence of the scattering means that shorter wavelengths are scattered more strongly than longer wavelengths. This results in the blue light coming from all regions of the sky. Rayleigh scattering is an approximation of the manner in which light scattering occurs within various media for which scattering particles have a small size. A portion of the beam of light coming from the sun scatters off molecules of gas, here, Rayleigh scattering primarily occurs through sunlights interaction with randomly located air molecules
13.
Backstay
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A backstay is a piece of standing rigging on a sailing vessel that runs from the mast to either its transom or rear quarter, counteracting the forestay and jib. It is an important sail trim control and has an effect on the shape of the mainsail. Backstays are generally adjusted by block and tackle, hydraulic adjusters, backstays may be permanent or running. A permanent backstay is attached to the top of the mast, running backstays appear in pairs attached about two-thirds of the way up the mast. In general, most modern sailboats will have a permanent backstay, backstays are not always found on all vessels, especially smaller ones. A permanent backstay is attached at the top of the mast, in a masthead rig, tensioning the permanent backstay will directly tension the forestay. This control is used to adjust the amount of sag in the headsail, increased mast bend tends to reduce the draft of the mainsail. A running backstay always attaches to the mast at a point below the top of the mast and is used in conjunction with a permanent backstay. Running backstays are found on both masthead rigs and fractional rigs, there are some rigs for which running backstays may be used without a permanent backstay. This occurs most often where the mainsail has a significant roach or a large mainsail. Gaff rigged boats invariably have running backstays with no permanent backstay, in both of these cases the mainsail extends aft of a line from masthead to stern, and so a permanent backstay would interfere with the operation of the sail. As a direct consequence of its attachment point a running backstay is always adjustable because it must be engaged and disengaged during every tack or jibe. Adjusting the tension on the running backstay has two effects, First, the forestay is tensioned and Second, mast bend is increased, the overall effect of tensioning the running backstay is a shallower mainsail combined with a reduction in headsail sag. Both effects are desirable as the wind increases
14.
Jacob's Ladder
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It has since been used as a symbolic reference in various other contexts. The description of Jacobs ladder appears in Genesis 28, 10-19, Jacob left Beersheba and he came to the place and stayed there that night, because the sun had set. Taking one of the stones of the place, he put it under his head and lay down in that place to sleep. And he dreamed, and behold, there was a set up on the earth, and the top of it reached to heaven, and behold. Behold, I am with you and will keep you wherever you go, then Jacob awoke from his sleep and said, Surely the Lord is in this place, and I did not know it. And he was afraid, and said, This is none other than the house of God, afterwards, Jacob names the place, Bethel. The classic Torah commentaries offer several interpretations of Jacobs ladder, according to the Midrash, the ladder signified the exiles which the Jewish people would suffer before the coming of the Messiah. First the angel representing the 70-year exile of Babylonia climbed up 70 rungs, then the angel representing the exile of Persia went up a number of steps, and fell, as did the angel representing the exile of Greece. Only the fourth angel, which represented the final exile of Rome/Edom, Jacob feared that his children would never be free of Esaus domination, but God assured him that at the End of Days, Edom too would come falling down. Another interpretation of the keys into the fact that the angels first ascended. The Midrash explains that Jacob, as a man, was always accompanied by angels. When he reached the border of the land of Canaan, the angels who were assigned to the Holy Land went back up to Heaven, when Jacob returned to Canaan he was greeted by the angels who were assigned to the Holy Land. Yet another interpretation is this, The place at which Jacob stopped for the night was in reality Mount Moriah, the ladder therefore signifies the bridge between Heaven and earth, as prayers and sacrifices offered in the Holy Temple soldered a connection between God and the Jewish people. Moreover, the ladder alludes to the giving of the Torah as another connection between heaven and earth. In this interpretation, it is significant that the Hebrew word for ladder, sulam. The Hellenistic Jewish philosopher Philo, born in Alexandria, presents his interpretation of the ladder in the first book of his De somniis. There he gives four interpretations, which are not mutually exclusive, The angels represent souls descending to, in the second interpretation the ladder is the human soul and the angels are Gods logoi, pulling the soul up in distress and descending in compassion. In the third view the dream depicts the ups and downs of the life of the practiser, finally the angels represent the continually changing affairs of men
15.
Ancient Greece
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Ancient Greece was a civilization belonging to a period of Greek history from the Greek Dark Ages of the 12th-9th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and this was followed by the period of Classical Greece, an era that began with the Greco-Persian Wars, lasting from the 5th to 4th centuries BC. Due to the conquests by Alexander the Great of Macedonia, Hellenistic civilization flourished from Central Asia to the end of the Mediterranean Sea. Classical Greek culture, especially philosophy, had a influence on ancient Rome. For this reason Classical Greece is generally considered to be the culture which provided the foundation of modern Western culture and is considered the cradle of Western civilization. Classical Antiquity in the Mediterranean region is considered to have begun in the 8th century BC. Classical Antiquity in Greece is preceded by the Greek Dark Ages and this period is succeeded, around the 8th century BC, by the Orientalizing Period during which a strong influence of Syro-Hittite, Jewish, Assyrian, Phoenician and Egyptian cultures becomes apparent. The end of the Dark Ages is also dated to 776 BC. The Archaic period gives way to the Classical period around 500 BC, Ancient Periods Astronomical year numbering Dates are approximate, consult particular article for details The history of Greece during Classical Antiquity may be subdivided into five major periods. The earliest of these is the Archaic period, in which artists made larger free-standing sculptures in stiff, the Archaic period is often taken to end with the overthrow of the last tyrant of Athens and the start of Athenian Democracy in 508 BC. It was followed by the Classical period, characterized by a style which was considered by observers to be exemplary, i. e. classical, as shown in the Parthenon. This period saw the Greco-Persian Wars and the Rise of Macedon, following the Classical period was the Hellenistic period, during which Greek culture and power expanded into the Near and Middle East. This period begins with the death of Alexander and ends with the Roman conquest, Herodotus is widely known as the father of history, his Histories are eponymous of the entire field. Herodotus was succeeded by authors such as Thucydides, Xenophon, Demosthenes, Plato, most of these authors were either Athenian or pro-Athenian, which is why far more is known about the history and politics of Athens than those of many other cities. Their scope is limited by a focus on political, military and diplomatic history, ignoring economic. In the 8th century BC, Greece began to emerge from the Dark Ages which followed the fall of the Mycenaean civilization, literacy had been lost and Mycenaean script forgotten, but the Greeks adopted the Phoenician alphabet, modifying it to create the Greek alphabet. The Lelantine War is the earliest documented war of the ancient Greek period and it was fought between the important poleis of Chalcis and Eretria over the fertile Lelantine plain of Euboea. Both cities seem to have suffered a decline as result of the long war, a mercantile class arose in the first half of the 7th century BC, shown by the introduction of coinage in about 680 BC
16.
Evaporation
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Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substance. The other type of vaporization is boiling, which is characterized by bubbles of saturated vapor forming in the liquid phase, steam produced in a boiler is another example of evaporation occurring in a saturated vapor phase. Evaporation that occurs directly from the solid phase below the melting point, on average, a fraction of the molecules in a glass of water have enough heat energy to escape from the liquid. The water in the glass will be cooled by the evaporation until an equilibrium is reached where the air supplies the amount of heat removed by the evaporating water, in an enclosed environment the water would evaporate until the air is saturated. With sufficient temperature, the liquid would turn into vapor quickly, when the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with energy to escape. Evaporation is an part of the water cycle. The sun drives evaporation of water from oceans, lakes, moisture in the soil, in hydrology, evaporation and transpiration are collectively termed evapotranspiration. Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor, when only a small proportion of the molecules meet these criteria, the rate of evaporation is low. Since the kinetic energy of a molecule is proportional to its temperature, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid decreases. This phenomenon is also called evaporative cooling and this is why evaporating sweat cools the human body. Evaporation also tends to proceed quickly with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure. For example, laundry on a line will dry more rapidly on a windy day than on a still day. Three key parts to evaporation are heat, atmospheric pressure, on a molecular level, there is no strict boundary between the liquid state and the vapor state. Instead, there is a Knudsen layer, where the phase is undetermined, because this layer is only a few molecules thick, at a macroscopic scale a clear phase transition interface cannot be seen. It is just that the process is slower and thus significantly less visible. If evaporation takes place in an area, the escaping molecules accumulate as a vapor above the liquid. Many of the return to the liquid, with returning molecules becoming more frequent as the density
17.
Sunburst
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A sunburst is a design or figure commonly used in architectural ornaments and design patterns. It consists of rays or beams radiating out from a disk in the manner of sunbeams. Sometimes part of a sunburst, a semicircular or semi-elliptical shape, is used, in architecture, the sunburst is often used in window designs, including fanlights and rose windows, as well as in decorative motifs. The sunburst motif is characteristic of Baroque church metalwork, especially monstrances and votive crowns, a sunburst is frequently used in emblems and military decorations. In information visualization, a sunburst diagram or sunburst chart is a pie chart used to represent the proportion of different values found at each level in a hierarchy
18.
Volumetric lighting
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Volumetric lighting is a technique used in 3D computer graphics to add lighting effects to a rendered scene. It allows the viewer to see beams of light shining through the environment, seeing sunbeams streaming through a window is an example of volumetric lighting. The term seems to have been introduced from cinematography and is now applied to 3D modelling and rendering especially in the field of 3D gaming. Volumetric lighting requires two components, a light space shadow map, and a depth buffer, starting at the near clip plane of the camera, the whole scene is traced and sampling values are accumulated into the input buffer. For each sample, it is determined if the sample is lit by the source of light being processed using the map as a comparison. Only lit samples will affect final pixel color and this basic technique works, but requires more optimization to function in real time. One way to optimize volumetric lighting effects is to render the lighting volume at a coarser resolution than that which the graphics context is using. This creates some bad aliasing artifacts, but that is easily touched up with a blur and you can also use stencil buffer like with the shadow volume technique. Another technique can also be used to provide usually satisfying, if inaccurate volumetric lighting effects, the algorithm functions by blurring luminous objects away from the center of the main light source. Generally, the transparency is reduced with each blur step. Note that this requires a source of light. Crepuscular rays Airglow 3D graphics terms dictionary at Tweak3D. net
19.
Antelope Canyon
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Antelope Canyon is a slot canyon in the American Southwest. It is located on Navajo land east of Page, Arizona, Antelope Canyon includes two separate, scenic slot canyon sections, referred to individually as Upper Antelope Canyon or The Crack, and Antelope Canyon or The Corkscrew. The Navajo name for Upper Antelope Canyon is Tsé bighánílíní, which means the place where water runs through rocks, Lower Antelope Canyon is Hazdistazí, or spiral rock arches. Both are located within the LeChee Chapter of the Navajo Nation, Antelope Canyon was formed by erosion of Navajo Sandstone, primarily due to flash flooding and secondarily due to other sub-aerial processes. Rainwater, especially during monsoon season, runs into the basin above the slot canyon sections, picking up speed. Over time the passageways eroded away, making the corridors deeper, flooding in the canyon still occurs. A flood occurred on October 30,2006, that lasted 36 hours, Antelope Canyon is a popular location for photographers and sightseers, and a source of tourism business for the Navajo Nation. Private tour companies have been permitted to offer tours since 1987 and it has been accessible by tour only since 1997, when the Navajo Tribe made it a Navajo Tribal Park. Photography within the canyons is difficult due to the exposure range made by light reflecting off the canyon walls. Upper Antelope Canyon is called Tsé bighánílíní, the place where water runs through rocks by the Navajo and it is the most frequently visited by tourists for two reasons. First, its entrance and entire length are at ground level, second, beams are much more common in Upper than in Lower. Beams occur most often in the months, as they require the sun to be high in the sky. Winter colors are a more muted like the photo displayed here. Summer months provide two types of lighting, light beams start to peek into the canyon March 20 and disappear October 7 each year. Lower Antelope Canyon, called Hazdistazí, or spiral rock arches by the Navajo Indians, are located a few miles away, prior to the installation of metal stairways, visiting the canyon required climbing along pre-installed ladders in certain areas. Even following the installation of stairways, it is a difficult hike than Upper Antelope. It is longer, narrower in spots, and even footing is not available in all areas, at the end, the climb out requires several flights of stairs. Despite these limitations, Lower Antelope Canyon draws a number of photographers
20.
Arizona
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Arizona is a state in the southwestern region of the United States. It is also part of the Western United States and the Mountain West states and it is the sixth largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix, Arizona is one of the Four Corners states. It has borders with New Mexico, Utah, Nevada, California, and Mexico, Arizonas border with Mexico is 389 miles long, on the northern border of the Mexican states of Sonora and Baja California. Arizona is the 48th state and last of the states to be admitted to the Union. Historically part of the territory of Alta California in New Spain, after being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase, Southern Arizona is known for its desert climate, with very hot summers and mild winters. There are ski resorts in the areas of Flagstaff, Alpine, in addition to the Grand Canyon National Park, there are several national forests, national parks, and national monuments. To the European settlers, their pronunciation sounded like Arissona, the area is still known as alĭ ṣonak in the Oodham language. Another possible origin is the Basque phrase haritz ona, as there were numerous Basque sheepherders in the area, There is a misconception that the states name originated from the Spanish term Árida Zona. See also lists of counties, islands, rivers, lakes, state parks, national parks, Arizona is in the Southwestern United States as one of the Four Corners states. Arizona is the sixth largest state by area, ranked after New Mexico, of the states 113,998 square miles, approximately 15% is privately owned. The remaining area is public forest and park land, state trust land, Arizona is well known for its desert Basin and Range region in the states southern portions, which is rich in a landscape of xerophyte plants such as the cactus. This regions topography was shaped by volcanism, followed by the cooling-off. Its climate has hot summers and mild winters. The state is well known for its pine-covered north-central portion of the high country of the Colorado Plateau. Like other states of the Southwest United States, Arizona has an abundance of mountains, despite the states aridity, 27% of Arizona is forest, a percentage comparable to modern-day France or Germany. The worlds largest stand of pine trees is in Arizona
21.
Airglow
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Airglow is a faint emission of light by a planetary atmosphere. In the case of Earths atmosphere, this phenomenon causes the night sky never to be completely dark, even after the effects of starlight. The airglow phenomenon was first identified in 1868 by Swedish physicist Anders Ångström, since then, it has been studied in the laboratory, and various chemical reactions have been observed to emit electromagnetic energy as part of the process. Scientists have identified some of those processes that would be present in Earths atmosphere and it is not noticeable during the daytime because of the scattered light from the sun. Even at the best ground-based observatories, airglow limits the sensitivity of telescopes at visible wavelengths, partly for this reason, space-based telescopes such as the Hubble Space Telescope can observe much fainter objects than current ground-based telescopes at visible wavelengths. The airglow at night may be enough to be noticed by an observer and is generally bluish in colour. Very low down, however, atmospheric extinction reduces the apparent brightness of the airglow, one airglow mechanism is when an atom of nitrogen combines with an atom of oxygen to form a molecule of nitric oxide. In the process, a photon is emitted and this photon may have any of several different wavelengths characteristic of nitric oxide molecules. The free atoms are available for process, because molecules of nitrogen and oxygen are dissociated by solar energy in the upper reaches of the atmosphere. Other species that can create air glow in the atmosphere are hydroxyl, atomic oxygen, the sky brightness is typically quoted in units of astronomical magnitudes per square arcsecond of sky. 0×10−12 W cm−2 µm−1.5 × S0 × B h ν. This gives the number of photons from airglow, Na, N a =10 −23 /2, a hypothetical 8 m Hubble telescope would take about 30 minutes. A space telescope isnt restricted by the field, since they are not impacted by airglow. Scientific experiments have been conducted to induce airglow by directing high-power radio emissions at the Earths ionosphere and these radiowaves interact with the ionosphere to induce faint but visible optical light at specific wavelengths under certain conditions. SwissCube-1 is a Swiss satellite operated by Ecole Polytechnique Fédérale de Lausanne, the spacecraft is a single unit CubeSat, which was designed to conduct research into airglow within the Earths atmosphere and to develop technology for future spacecraft. Though SwissCube-1 is rather small and weighs less than 1 kg, the first SwissCube-1 image came down on February 18,2011 and was quite black with some thermal noise on it. The first airglow image came down on March 3,2011 and this image has been converted to the human optical range from its near-infrared measurement. This image provides a measurement of the intensity of the phenomenon in the near-infrared. The range measured is from 500 to 61400 photons, with a resolution of 500 photons, the Venus Express spacecraft contains an infrared sensor which has detected near-IR emissions from the upper atmosphere of Venus
22.
Light beam
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A light beam or beam of light is a directional projection of light energy radiating from a light source. Sunlight forms a light beam when filtered through media such as clouds, foliage, to artificially produce a light beam, a lamp and a parabolic reflector is used in many lighting devices such as spotlights, car headlights, PAR Cans and LED housings. Light from certain types of laser has the smallest possible beam divergence. From the side, a beam of light is visible if part of the light is scattered by objects, tiny particles like dust, water droplets, hail, snow, or smoke. If there are objects in the light path, then it appears as a continuous beam. In any case, this scattering of light from a beam, flashlight, beam directed by hand Headlight, forward beam, the lamp is mounted in a vehicle, or on the forehead of a person, e. g. The difference between the two is that the fog itself is also a visual effect, Laser lighting display- Laser beams are often used for visual effects, often in combination with music. This also used to be done for movie premieres, the waving searchlight beams are still to be seen as an element in the logo of the 20th Century Fox movie studio
23.
Tyndall effect
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The Tyndall effect, also known as Tyndall scattering, is light scattering by particles in a colloid or else particles in a very fine suspension. It is named after the 19th-century physicist John Tyndall and it is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth power of the frequency, so blue light is scattered much more strongly than red light. An example in everyday life is the colour sometimes seen in the smoke emitted by motorcycles. Under the Tyndall effect, the light is more transmitted while the shorter-wavelength light is more reflected via scattering. e. Somewhat below or near the wavelength of visible light, Rayleigh scattering is defined by a mathematical formula that requires the light-scattering particles to be far smaller than the wavelength of the light. For a dispersion of particles to qualify for the Rayleigh formula, the particle sizes need to be below roughly 40 nanometres, colloidal particles are bigger, and are in the rough vicinity of the size of a wavelength of light. Tyndall scattering, i. e. colloidal particle scattering, is more intense than Rayleigh scattering due to the bigger particle sizes involved. The importance of the particle size factor for intensity can be seen in the large exponent it has in the statement of the intensity of Rayleigh scattering. If the colloid particles are spheroid, Tyndall scattering can be analyzed in terms of Mie theory. Light scattering by particles of complex shape are described by the T-matrix method, a blue iris in an eye is due to Tyndall scattering in a translucent layer in the iris. Brown and black irises have the same layer except with more melanin in it, in the absence of melanin, the layer is translucent and a noticeable portion of the light that enters this translucent layer re-emerges via a scattered path. That is, there is backscatter, the redirection of the back out to the open air. Scattering takes place to an extent at the shorter wavelengths. The longer wavelengths tend to pass straight through the translucent layer with unaltered paths, and then encounter the next layer further back in the iris, thus, the longer wavelengths are not reflected back to the open air as much as the shorter wavelengths are. Because the shorter wavelengths are the wavelengths, this gives rise to a blue hue in the light that comes out of the eye. The blue iris is an example of a color, in contradistinction to a pigment color. The complete absence of pigment in eyes causes the eye to appear red, on a day when the sky is overcast, the sunlight passes through the turbid layer of the clouds, resulting in scattered, diffuse light on the ground. This does not exhibit Tyndall scattering because the droplets are larger than the wavelength of light
24.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
25.
Wikimedia Commons
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Wikimedia Commons is an online repository of free-use images, sound, and other media files. It is a project of the Wikimedia Foundation, the repository contains over 38 million media files. In July 2013, the number of edits on Commons reached 100,000,000, the project was proposed by Erik Möller in March 2004 and launched on September 7,2004. The expression educational is to be according to its broad meaning of providing knowledge. Wikimedia Commons itself does not allow fair use or uploads under non-free licenses, for this reason, Wikimedia Commons always hosts freely licensed media and deletes copyright violations. The default language for Commons is English, but registered users can customize their interface to use any other user interface translations. Many content pages, in particular policy pages and portals, have also translated into various languages. Files on Wikimedia Commons are categorized using MediaWikis category system, in addition, they are often collected on individual topical gallery pages. While the project was proposed to also contain free text files. In 2012, BuzzFeed described Wikimedia Commons as littered with dicks, in 2010, Wikipedia co-founder Larry Sanger reported Wikimedia Commons to the FBI for hosting sexualized images of children known as lolicon. Wales responded to the backlash from the Commons community by voluntarily relinquishing some site privileges, over time, additional functionality has been developed to interface Wikimedia Commons with the other Wikimedia projects. Specialized uploading tools and scripts such as Commonist have been created to simplify the process of uploading large numbers of files. In order to free content photos uploaded to Flickr, users can participate in a defunct collaborative external review process. The site has three mechanisms for recognizing quality works, one is known as Featured pictures, where works are nominated and other community members vote to accept or reject the nomination. This process began in November 2004, another process known as Quality images began in June 2006, and has a simpler nomination process comparable to Featured pictures. Quality images only accepts works created by Wikimedia users, whereas Featured pictures additionally accepts nominations of works by third parties such as NASA, the three mentioned processes select a slight part from the total number of files. However, Commons collects files of all quality levels, from the most professional level across simple documental, files with specific defects can be tagged for improvement and warning or even proposed for deletion but there exists no process of systematic rating of all files. The site held its inaugural Picture of the Year competition, for 2006, all images that were made a Featured picture during 2006 were eligible, and voted on by eligible Wikimedia users during two rounds of voting
