obliquity

Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally, "law of the stars") is the science of celestial objects and phenomena that originate outside the Earth's atmosphere, such as stars, planets, comets, galaxies, and the cosmic background radiation. It is concerned with the formation and development of the universe, the evolution and physical and chemical properties of celestial objects and the calculation of their motions. Astronomical observations are ...

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• Astronomy - Divisions
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• Astronomy - History of astronomy
• Astronomy - Timelines in astronomy
• Astronomy - Astronomy tools

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A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. A glacier is formed by multi-year ice accretion in sloping terrain. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers can be found on every continent except Australia. Geologic features associated with glaciers include end, lateral, ground and medial moraines that form from glacially tran ...

Including:

• Glacier - Types of glaciers
• Glacier - Formation of glaciers
• Glacier - Anatomy of a glacier
• Glacier - Glacial motion
• Glacier - Speed of glacial movement
• Glacier - Moraines
• Glacier - Drumlins
• Glacier - Glacial erosion
• Glacier - Glacial valleys
• Glacier - Arêtes and horns
• Glacier - Sheepback rock
• Glacier - Alluvial stratification
• Glacier - Deposits in contact with ice
• Glacier - Loess deposits
• Glacier - Isostatic rebound
• Glacier - Ice ages
• Glacier - Ice age divisions
• Glacier - Causes of ice ages
• Glacier - Plate tectonics

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An ice age is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ("glaciation"). Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ice age is used to refer to colder periods wit ...

Including:

• Ice age - Origin of ice age theory
• Ice age - Major ice ages
• Ice age - Interglacials
• Ice age - Causes of ice ages
• Ice age - Recent glacial and interglacial phases
• Ice age - Glaciation in North America
• Ice age - Reference

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As the Earth spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Although the curves have a large number of sinusoidal components, a few components are dominant. Milankovitch studied changes in the eccentricity, obliquity, and precession of Earth's movements. Such changes in movement and orientation change the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Changes near the north polar area are considered important due to the large amount of land, which reacts to such changes more quic ...

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Milankovitch cycles, Milankovitch cycles - Earth's movements, Milankovitch cycles - Orbital shape, Milankovitch cycles - Axial tilt, Milankovitch cycles - Axial orientation, Milankovitch cycles - Orbital inclination, Milankovitch cycles - Problems, Milankovitch cycles - 100 ky problem, Milankovitch cycles - 400 ky problem, Milankovitch cycles - Stage 5 problem, Milankovitch cycles - Effect exceeds cause, Milankovitch cycles - The unsplit peak problem, Milankovitch cycles - The transition problem, Milankovitch cycles - Present conditions, Milankovitch cycles - The future

Read more here: » Milankovitch cycles: Encyclopedia II - Milankovitch cycles - Earth's movements

The 19 reference ellipsoid models listed below have had utility in geodetic work and many are still in use. The older ellipsoids are named for the individual who derived them and the year of development is given. In 1887 the English mathematician Col Alexander Ross Clarke CB FRS RE was awarded the Gold Medal of the Royal Society for his work in determining the figure of the Earth. The international ellipsoid was developed by John Fillmore Hayford in 1910 and adopted by the International Union of Geodesy and Geo ...

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Figure of the Earth, Figure of the Earth - Ellipsoid of revolution, Figure of the Earth - Historical Earth ellipsoids, Figure of the Earth - More complicated figures, Figure of the Earth - Geoid, Figure of the Earth - Correlations to Geophysics and Geology, Figure of the Earth - Earth rotation and Earth's interior, Figure of the Earth - Global and regional gravity field, Figure of the Earth - Literature

Read more here: » Figure of the Earth: Encyclopedia II - Figure of the Earth - Historical Earth ellipsoids

The average energy density of solar radiation just above the Earth's atmosphere, in a plane perpendicular to the rays, is about 1367 W/m², a value called the solar constant (although it fluctuates by a few parts per thousand from day to day). The Earth receives a total amount of radiation determined by its cross section (π R2), but as the planet rotates this energy is distributed across the entire surface area (4 π R2). Hence, the average incoming solar radiation (known as "insolation") is 1/4th the solar constant or ~342 W/m². At any given location and time, the amount received at ...

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Solar radiation, Solar radiation - Climate effect of solar radiation

Read more here: » Solar radiation: Encyclopedia II - Solar radiation - Climate effect of solar radiation

Rocks and sediments are added to glaciers through various processes. Glaciers erode the terrain principally through two methods: abrasion and plucking. As the glacier flows over the bedrock's fractured surface, it softens and lifts blocks of rock that are brought into the ice. This process is known as plucking, and it is produced when subglacial water penetrates the fractures and the subsequent freezing expansion separates them from the bedrock. When the water expands, it acts as a lever that loosens the rock by lifting it. This way, sediments of a ...

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Glacier, Glacier - Types of glaciers, Glacier - Formation of glaciers, Glacier - Anatomy of a glacier, Glacier - Glacial motion, Glacier - Speed of glacial movement, Glacier - Moraines, Glacier - Drumlins, Glacier - Glacial erosion, Glacier - Glacial valleys, Glacier - Arêtes and horns, Glacier - Sheepback rock, Glacier - Alluvial stratification, Glacier - Deposits in contact with ice, Glacier - Loess deposits, Glacier - Isostatic rebound, Glacier - Ice ages, Glacier - Ice age divisions, Glacier - Causes of ice ages, Glacier - Plate tectonics

Read more here: » Glacier: Encyclopedia II - Glacier - Glacial erosion

The cause of ice ages remains controversial for both the large-scale ice age periods and the smaller ebb and flow of glacial/interglacial periods within an ice age. The general consensus is that it is a combination of up to three different factors: atmospheric composition (particularly the fraction of CO2 and methane), changes in the Earth's orbit around the Sun known as Milankovitch cycles (and possibly the Sun's orbit around the g ...

See also:

Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Causes of ice ages

In ancient Greece and other early civilizations, astronomy consisted largely of astrometry, measuring positions of stars and planets in the sky. Later, with the work of astronomers Kepler and Newton, whose work led to the development of celestial mechanics, the mathematical prediction of the motions of celestial bodies interacting gravitationally became the focus of astronomy. This was applied to solar system objects in particular. Motions and positions of objects are now more easily determined, and modern astronomy is more concerned with observing and understanding the actua ...

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Astronomy, Astronomy - Divisions, Astronomy - By subject or problem addressed, Astronomy - Ways of obtaining information, Astronomy - History of astronomy, Astronomy - Timelines in astronomy, Astronomy - Astronomy tools

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Since the Earth is in fact flattened slightly at the poles and bulges somewhat at the equator, the geometrical figure used in geodesy to most nearly approximate the shape of the Earth is an ellipsoid of revolution. The ellipsoid of revolution is the figure which would be obtained by rotating an ellipse about its shorter axis. An ellipsoid of revolution describing the figure of the Earth is called a reference ellipsoid. An ellipsoid of revolution is uniquely defined by specifying two dimensions. Geodesists, by convention, use the semim ...

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Figure of the Earth, Figure of the Earth - Ellipsoid of revolution, Figure of the Earth - Historical Earth ellipsoids, Figure of the Earth - More complicated figures, Figure of the Earth - Geoid, Figure of the Earth - Correlations to Geophysics and Geology, Figure of the Earth - Earth rotation and Earth's interior, Figure of the Earth - Global and regional gravity field, Figure of the Earth - Literature

Read more here: » Figure of the Earth: Encyclopedia II - Figure of the Earth - Ellipsoid of revolution

The possibility that the Earth's equator is an ellipse rather than a circle and therefore that the ellipsoid is triaxial has been a matter of scientific controversy for many years. Modern technological developments have furnished new and rapid methods for data collection and since the launching of the first Russian Sputnik, orbital data has been used to investigate the theory of ellipticity. A second theory, more complicated than triaxiality, proposed that observed long periodic orbital variations of the first Earth satellites indicat ...

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Figure of the Earth, Figure of the Earth - Ellipsoid of revolution, Figure of the Earth - Historical Earth ellipsoids, Figure of the Earth - More complicated figures, Figure of the Earth - Geoid, Figure of the Earth - Correlations to Geophysics and Geology, Figure of the Earth - Earth rotation and Earth's interior, Figure of the Earth - Global and regional gravity field, Figure of the Earth - Literature

Read more here: » Figure of the Earth: Encyclopedia II - Figure of the Earth - More complicated figures

It was stated earlier that measurements are made on the apparent or topographic surface of the Earth and it has just been explained that computations are performed on an ellipsoid. One other surface is involved in geodetic measurement: the geoid. In geodetic surveying, the computation of the geodetic coordinates of points is commonly performed on a reference ellipsoid closely approximating the size and shape of the Earth in the area of the survey. The actual measurements made on the surface of the Earth with certain instruments are however r ...

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Figure of the Earth, Figure of the Earth - Ellipsoid of revolution, Figure of the Earth - Historical Earth ellipsoids, Figure of the Earth - More complicated figures, Figure of the Earth - Geoid, Figure of the Earth - Correlations to Geophysics and Geology, Figure of the Earth - Earth rotation and Earth's interior, Figure of the Earth - Global and regional gravity field, Figure of the Earth - Literature

Read more here: » Figure of the Earth: Encyclopedia II - Figure of the Earth - Geoid

The Wisconsinan glaciation has had a considerable effect on the landscape of the Northern Hemisphere. In North America, the Great Lakes and the Finger Lakes were carved by ice's deepening of old valleys, and most of the lakes in Minnesota and Wisconsin were gouged out by glaciers, to be filled with water later when the glaciers melted. The old Teays River drainage system was radically altered and largely reshaped into the Ohio River drainage system. Other rivers were dammed and diverted to new channels, such as the Niagara, which formed a dr ...

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Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Glaciation in North America

In between ice ages, there are multi-million year periods of more temperate, almost tropical, climate, but also within the ice ages (or at least within the last one), temperate and severe periods occur. The colder periods are called 'glacial periods', the warmer periods 'interglacials', such as the Eemian interglacial era. We are in an interglacial period now, the last retreat ending about 10,000 years ago. There appears to be a folk wisdom that "the typical interglacial period lasts ~12,000 years" but this is hard to substantiate fro ...

See also:

Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Interglacials

The idea that, in the past, glaciers had been far more extensive was folk knowledge in some alpine regions of Europe (Imbrie and Imbrie, p25, quote a woodcutter telling Jean de Charpentier of the former extent of the Swiss Grimsel glacier). No single person invented the idea [1]. Between 1825 and 1833, Charpentier assembled evidence in support of this idea. In 1836 Charpentier convinced Louis Agassiz of the theory, and Agassiz published it ...

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Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Origin of ice age theory

Figure of the Earth - Earth rotation and Earth's interior. Dertermining the exact figure of the Earth is not only a geodetic operation or a task of geometry, but is also related to geophysics. Without any idea of the Earth's interior, we can state a "constant density" of 5.5 g/cm³ and, according to theoretical arguments (see Leonhard Euler, A. Wangerin, etc.), such a body rotating like the Earth would have an obliquity of 1:230. In fact the measured flattening is 1:298.25, which is more similar to a spher ...

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Figure of the Earth, Figure of the Earth - Ellipsoid of revolution, Figure of the Earth - Historical Earth ellipsoids, Figure of the Earth - More complicated figures, Figure of the Earth - Geoid, Figure of the Earth - Correlations to Geophysics and Geology, Figure of the Earth - Earth rotation and Earth's interior, Figure of the Earth - Global and regional gravity field, Figure of the Earth - Literature

Read more here: » Figure of the Earth: Encyclopedia II - Figure of the Earth - Correlations to Geophysics and Geology

In early times, astronomy only comprised the observation and predictions of the motions of the naked-eye objects. Aristotle said that the Earth was the center of the Universe and everything rotated around it in orbits that were perfect circles. Aristotle had to be right because people thought that Earth had to be in the center with everything rotating around it because the wind would not scatter leaves, and birds would only fly in one direction. For a long time, people thought that A ...

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Astronomy, Astronomy - Divisions, Astronomy - By subject or problem addressed, Astronomy - Ways of obtaining information, Astronomy - History of astronomy, Astronomy - Timelines in astronomy, Astronomy - Astronomy tools

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The snow which forms glaciers is subject to repeated freezing and thawing, which changes it into a form of granular ice called névé. Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacial ice contains minute air bubbles as a result, giving it a distinctive blue tint due to Rayleigh scattering. The lower layers of glacial ice flow and deform plastically under the pressure, allowing the glacie ...

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Glacier, Glacier - Types of glaciers, Glacier - Formation of glaciers, Glacier - Anatomy of a glacier, Glacier - Glacial motion, Glacier - Speed of glacial movement, Glacier - Moraines, Glacier - Drumlins, Glacier - Glacial erosion, Glacier - Glacial valleys, Glacier - Arêtes and horns, Glacier - Sheepback rock, Glacier - Alluvial stratification, Glacier - Deposits in contact with ice, Glacier - Loess deposits, Glacier - Isostatic rebound, Glacier - Ice ages, Glacier - Ice age divisions, Glacier - Causes of ice ages, Glacier - Plate tectonics

Read more here: » Glacier: Encyclopedia II - Glacier - Formation of glaciers

In between ice ages, there are multi-million year periods of more temperate climate, but also within the ice ages (or at least within the last one), temperate and severe periods occur. The colder periods are called 'glacial periods', the warmer periods 'interglacials', such as the Eemian interglacial era. We are in an interglacial period now, the last retreat ending about 10,000 years ago. There appears to be a folk wisdom that "the typical interglacial period lasts ~12,000 years" but this is hard to substantiate from the evidence of ...

See also:

Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Interglacials

There have been at least four major ice ages in the Earth's past. The earliest hypothesized ice age is believed to have occurred around 2.7 to 2.3 billion (109) years ago during the early Proterozoic Age. Main article: Snowball Earth. The earliest well-documented ice age, and probably the most severe of the last 1 billion years, occurred from 800 to 600 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended t ...

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Ice age, Ice age - Origin of ice age theory, Ice age - Major ice ages, Ice age - Interglacials, Ice age - Causes of ice ages, Ice age - Recent glacial and interglacial phases, Ice age - Glaciation in North America, Ice age - Reference

Read more here: » Ice age: Encyclopedia II - Ice age - Major ice ages