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Arctic Circle
The Arctic Circle is one of the two polar circles, and the northernmost of the five major circle of latitude, circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circle marks the southernmost latitude at which, on the winter solstice in the Northern Hemisphere, the Sun does not rise all day, and on the Northern Hemisphere's summer solstice, the Sun does not set. These phenomena are referred to as polar night and midnight sun respectively, and the further north one progresses, the more obvious this becomes. For example, in the Russian port city of Murmansk, three degrees north of the Arctic Circle, the Sun stays below the horizon for 20 days before and after the winter solstice, and above the horizon for 20 days before and after the summer solstice. The position of the Arctic Circle is not fixed and currently runs north of the Equator. Its latitude depends on Earth's axial tilt, which axial precession, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circle Of Latitude
A circle of latitude or line of latitude on Earth is an abstract east–west small circle connecting all locations around Earth (ignoring elevation) at a given latitude coordinate line. Circles of latitude are often called parallels because they are Parallel (geometry), parallel to each other; that is, planes that contain any of these circles never Intersection, intersect each other. A location's position along a circle of latitude is given by its longitude. Circles of latitude are unlike circles of longitude, which are all great circles with the centre of Earth in the middle, as the circles of latitude get smaller as the distance from the Equator increases. Their length can be calculated by a common sine or cosine function. For example, the 60th parallel north or 60th parallel south, south is half as long as the Equator (disregarding Earth's minor flattening by 0.335%), stemming from \cos(60^) = 0.5. On the Mercator projection or on the Gall-Peters projection, a circle of la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mirage
A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meaning "to look at, to wonder at". Mirages can be categorized as "inferior" (meaning lower), "superior" (meaning higher) and " Fata Morgana", one kind of superior mirage consisting of a series of unusually elaborate, vertically stacked images, which form one rapidly-changing mirage. In contrast to a hallucination, a mirage is a real optical phenomenon that can be captured on camera, since light rays are actually refracted to form the false image at the observer's location. What the image appears to represent, however, is determined by the interpretive faculties of the human mind. For example, inferior images on land are very easily mistaken for the reflections from a small body of water. Inferior mirage In an inferior mirage, the mirage im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atmospheric Refraction
Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. This refraction is due to the velocity of light through air decreasing (the refractive index increases) with increased density. Atmospheric refraction near the ground produces mirages. Such refraction can also looming and similar refraction phenomena, raise or lower, or stretch or shorten, the images of distant objects without involving mirages. turbulence, Turbulent air can make distant objects appear to twinkling, twinkle or shimmer. The term also applies to the refraction of sound. Atmospheric refraction is considered in measuring the position of both celestial and terrestrial objects. Astronomical or celestial refraction causes astronomical objects to appear higher above the horizon than they actually are. Terrestrial refraction usually causes terrestrial objects to Mirage#Superior ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solstice
A solstice is the time when the Sun reaches its most northerly or southerly sun path, excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around 20–22 June and 20–22 December. In many countries, the seasons of the year are defined by reference to the solstices and the equinoxes. The term ''solstice'' can also be used in a broader sense, as the day when this occurs. For locations not too close to the equator or the poles, the dates with the longest and shortest periods of daylight are the summer and winter solstices, respectively. Terms with no ambiguity as to which hemisphere is the context are "June solstice" and "December solstice", referring to the months in which they take place every year. Etymology The word ''solstice'' is derived from the Latin () and (), because at the solstices, the Sun's declination appears to "stand still"; that is, the seasonal movement of the Sun's sun path, daily path (as seen from Earth) paus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
December Solstice
The December solstice, also known as the southern solstice, is the solstice that occurs each December – typically on 21 December, but may vary by one day in either direction according to the Gregorian calendar. In the Northern Hemisphere, the December solstice is the winter solstice (the day with the shortest period of daylight), whilst in the Southern Hemisphere it is the summer solstice (the day with the longest period of daylight). During December solstice, the Sun is directly over the Tropic of Capricorn, located in the Southern Hemisphere. The December solstice is often seen as the middle of winter in the Northern Hemisphere and the middle of summer in the Southern Hemisphere. Solar year The December-solstice solar year is the solar year based on the December solstice. It is thus the length of time between adjacent December solstices. The length of the December-solstice year has been relatively stable between 6000 BC and AD 2000, in the range of 49 minutes 30 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
June Solstice
The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar. In the Northern Hemisphere, the June solstice is the summer solstice (the day with the longest period of daylight), while in the Southern Hemisphere it is the winter solstice (the day with the shortest period of daylight). It is also known as the northern solstice or summer solstice. During June solstice, the Sun is directly over the Tropic of Cancer, located in the northern hemisphere. Solar year The June solstice solar year is the solar year based on the June solstice. It is thus the length of time between adjacent June solstices. The length of the day on June solstice See also Astronomy * March equinox * September equinox * December solstice Holidays * Inti Raymi * Kupala Night * Midnight sun * Midsummer * We Tripantu * World Humanist Day References {{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Calenda ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polar Night
Polar night is a phenomenon that occurs in the polar regions of Earth, northernmost and southernmost regions of Earth when the Sun remains below the horizon for more than 24 hours. This only occurs inside the polar circles. The opposite phenomenon, polar day or midnight sun, occurs when the Sun remains above the horizon for more than 24 hours. There are multiple ways to define twilight, the gradual transition to and from darkness when the Sun is below the horizon. "Civil" twilight occurs when the Sun is between 0 and 6 degrees below the horizon. Nearby planets like Venus and bright stars like Sirius are visible during this period. "Nautical" twilight continues until the Sun is 12 degrees below the horizon. During nautical twilight, the horizon is visible enough for navigation. "Astronomical" twilight continues until the Sun has sunk 18 degrees below the horizon. Beyond 18 degrees, refracted sunlight is no longer visible. True night is defined as the period when the sun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Midnight Sun
Midnight sun, also known as polar day, is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When midnight sun is seen in the Arctic, the Sun appears to move from left to right. In Antarctica, the equivalent apparent motion is from right to left. This occurs at latitudes ranging from approximately 65°44' to exactly 90° north or south, and does not stop exactly at the Arctic Circle or the Antarctic Circle, due to refraction. The opposite phenomenon, polar night, occurs in winter, when the Sun stays below the horizon throughout the day. Geography Because there are no permanent human settlements south of the Antarctic Circle, apart from research stations, the countries and territories whose populations experience midnight sun are limited to those crossed by the Arctic Circle: Canada (Yukon, Nunavut, and Northwest Territories), Finland, Greenland, Ic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axial Tilt Vs Tropical And Polar Circles
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Axial may refer to: * one of the anatomical directions describing relationships in an animal body * In geometry: :* a geometric term of location :* an axis of rotation * In chemistry, referring to an axial bond * a type of modal frame, in music * axial-flow, a type of fan * the Axial Age in China, India, etc. * Axial Seamount and submarine volcano off Oregon, USA * Axial, Colorado, a ghost town See also *Axiality (other) *Axis (other) An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bear
Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout most of the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, and Eurasia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails. While the polar bear is mostly carnivorous, and the giant panda is mostly herbivorous, the remaining six species are omnivorous with varying diets. With the exception of courtship display, courting individuals and mothers with their young, bears are typically solitary animals. They may be diurnality, diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perseus Digital Library
The Perseus Digital Library, formerly known as the Perseus Project, is a free-access digital library founded by Gregory Crane in 1987 and hosted by the Department of Classical Studies of Tufts University. One of the pioneers of digital libraries, its self-proclaimed mission is to make the full record of humanity available to everyone. While originally focused on the ancient Greco -Roman world, it has since diversified and offers materials in Arabic, Germanic, English Renaissance literature, 19th century American documents and Italian poetry in Latin, and has sprouted several child projects and international cooperation. The current version, Perseus 4.0, is also known as the Perseus Hopper, and is mirrored by the University of Chicago. Purpose The Perseus Digital Library was created to provide access to materials of the history of humanity to everyone, with Gregory Crane, the editor-in-chief of the library, stating that "access to the cultural heritage of humanity is a righ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
