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This article is about the planet. For other uses, see Earth (disambiguation).
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Earth Astronomical symbol of Earth A planetary disk of white cloud formations, brown and green land masses, and dark blue oceans against a black background. The Arabian peninsula, Africa and Madagascar lie in the upper half of the disk, while Antarctica is at the bottom.
“The Blue Marble” photograph of Earth,
taken from Apollo 17
Designations
Alternative names Tellus or Terra,[note 1] Gaia
Orbital characteristics
Epoch J2000.0[note 2]
Aphelion 152,098,232 km
1.01671388 AU[note 3]
Perihelion 147,098,290 km
0.98329134 AU[note 3]
Semi-major axis 149,598,261 km
1.00000261 AU[1]
Eccentricity 0.01671123[1]
Orbital period 365.256363004 days[2]
1.000017421 yr
Average orbital speed 29.78 km/s[3]
107,200 km/h
Mean anomaly 357.51716°[3]
Inclination 7.155° to Sun’s equator
1.57869°[4] to invariable plane
Longitude of ascending node 348.73936°[3][note 4]
Argument of perihelion 114.20783°[3][note 5]
Satellites 1 natural (the Moon),
8,300+ artificial (as of 1 March 2001)[5]
Physical characteristics
Mean radius 6,371.0 km[6]
Equatorial radius 6,378.1 km[7][8]
Polar radius 6,356.8 km[9]
Flattening 0.0033528[10]
Circumference 40,075.017 km (equatorial)[8]
40,007.86 km (meridional)[11][12]
Surface area
510,072,000 km2[13][14][note 6] 148,940,000 km2 land (29.2 %)
361,132,000 km2 water (70.8 %)
Volume 1.08321×1012 km3[3]
Mass
5.97219×1024 kg[3]
3.0×10−6 Suns
Mean density 5.515 g/cm3[3]
Equatorial surface gravity 9.780327 m/s2[15]
0.99732 g
Escape velocity 11.186 km/s[3]
Sidereal rotation period 0.99726968 d[16]
23h 56m 4.100s
Equatorial rotation velocity 1,674.4 km/h (465.1 m/s)[17]
Axial tilt 23°26’21″.4119[2]
Albedo
0.367 (geometric)[3]
0.306 (Bond)[3]
Surface temp. min mean max
Kelvin 184 K[18] 288 K[19] 330 K[20]
Celsius −89.2 °C 15 °C 56.7 °C
Atmosphere
Surface pressure 101.325 kPa (MSL)
Composition 78.08% nitrogen (N2)[3] (dry air)
20.95% oxygen (O2)
0.93% argon
0.039% carbon dioxide[21]
About 1% water vapor (varies with climate)
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System’s four terrestrial planets. It is sometimes referred to as the world or the Blue Planet.[22]
Earth formed approximately 4.54 billion years ago, and life appeared on its surface within its first billion years.[23] Earth’s biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer, which together with Earth’s magnetic field blocked harmful solar radiation, and permitted formerly ocean-confined life to move safely to land.[24] The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. Estimates on how much longer the planet will be able to continue to support life range from 500 million years (myr), to as long as 2.3 billion years (byr).[25][26][27]
Earth’s lithosphere is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth’s poles are mostly covered with ice that is the solid ice of the Antarctic ice sheet and the sea ice that is the polar ice packs. The planet’s interior remains active, with a solid iron inner core, a liquid outer core that generates the magnetic field, and a thick layer of relatively solid mantle.
Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, the Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or one sidereal year.[note 7] The Earth’s axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet’s surface with a period of one tropical year (365.24 solar days).[28] The Moon is Earth’s only natural satellite. It began orbiting the Earth about 4.53 billion years ago (bya). The Moon’s gravitational interaction with Earth stimulates ocean tides, stabilizes the axial tilt, and gradually slows the planet’s rotation.
The planet is home to millions of species of life, including humans.[29] Both the mineral resources of the planet and the products of the biosphere contribute resources that are used to support a global human population.[30] These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including its personification as a planetary deity, its shape as flat, its position as the center of the universe, and in the modern Gaia Principle, as a single, self-regulating organism in its own right
from : http://en.wikipedia.org/wiki/Earth
This article is about the planet. For other uses, see Earth (disambiguation).
Page semi-protected
Earth Astronomical symbol of Earth A planetary disk of white cloud formations, brown and green land masses, and dark blue oceans against a black background. The Arabian peninsula, Africa and Madagascar lie in the upper half of the disk, while Antarctica is at the bottom.
“The Blue Marble” photograph of Earth,
taken from Apollo 17
Designations
Alternative names Tellus or Terra,[note 1] Gaia
Orbital characteristics
Epoch J2000.0[note 2]
Aphelion 152,098,232 km
1.01671388 AU[note 3]
Perihelion 147,098,290 km
0.98329134 AU[note 3]
Semi-major axis 149,598,261 km
1.00000261 AU[1]
Eccentricity 0.01671123[1]
Orbital period 365.256363004 days[2]
1.000017421 yr
Average orbital speed 29.78 km/s[3]
107,200 km/h
Mean anomaly 357.51716°[3]
Inclination 7.155° to Sun’s equator
1.57869°[4] to invariable plane
Longitude of ascending node 348.73936°[3][note 4]
Argument of perihelion 114.20783°[3][note 5]
Satellites 1 natural (the Moon),
8,300+ artificial (as of 1 March 2001)[5]
Physical characteristics
Mean radius 6,371.0 km[6]
Equatorial radius 6,378.1 km[7][8]
Polar radius 6,356.8 km[9]
Flattening 0.0033528[10]
Circumference 40,075.017 km (equatorial)[8]
40,007.86 km (meridional)[11][12]
Surface area
510,072,000 km2[13][14][note 6] 148,940,000 km2 land (29.2 %)
361,132,000 km2 water (70.8 %)
Volume 1.08321×1012 km3[3]
Mass
5.97219×1024 kg[3]
3.0×10−6 Suns
Mean density 5.515 g/cm3[3]
Equatorial surface gravity 9.780327 m/s2[15]
0.99732 g
Sidereal rotation period 0.99726968 d[16]
23h 56m 4.100s
Equatorial rotation velocity 1,674.4 km/h (465.1 m/s)[17]
Axial tilt 23°26’21″.4119[2]
Albedo
0.367 (geometric)[3]
0.306 (Bond)[3]
Surface temp. min mean max
Kelvin 184 K[18] 288 K[19] 330 K[20]
Celsius −89.2 °C 15 °C 56.7 °C
Atmosphere
Surface pressure 101.325 kPa (MSL)
Composition 78.08% nitrogen (N2)[3] (dry air)
20.95% oxygen (O2)
0.93% argon
0.039% carbon dioxide[21]
About 1% water vapor (varies with climate)
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System’s four terrestrial planets. It is sometimes referred to as the world or the Blue Planet.[22]
Earth formed approximately 4.54 billion years ago, and life appeared on its surface within its first billion years.[23] Earth’s biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer, which together with Earth’s magnetic field blocked harmful solar radiation, and permitted formerly ocean-confined life to move safely to land.[24] The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. Estimates on how much longer the planet will be able to continue to support life range from 500 million years (myr), to as long as 2.3 billion years (byr).[25][26][27]
Earth’s lithosphere is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth’s poles are mostly covered with ice that is the solid ice of the Antarctic ice sheet and the sea ice that is the polar ice packs. The planet’s interior remains active, with a solid iron inner core, a liquid outer core that generates the magnetic field, and a thick layer of relatively solid mantle.
Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, the Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or one sidereal year.[note 7] The Earth’s axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet’s surface with a period of one tropical year (365.24 solar days).[28] The Moon is Earth’s only natural satellite. It began orbiting the Earth about 4.53 billion years ago (bya). The Moon’s gravitational interaction with Earth stimulates ocean tides, stabilizes the axial tilt, and gradually slows the planet’s rotation.
The planet is home to millions of species of life, including humans.[29] Both the mineral resources of the planet and the products of the biosphere contribute resources that are used to support a global human population.[30] These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including its personification as a planetary deity, its shape as flat, its position as the center of the universe, and in the modern Gaia Principle, as a single, self-regulating organism in its own right
from : http://en.wikipedia.org/wiki/Earth
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