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Learn about Earth, the third planet from the Sun and the only place with life. Find out about its features, climate, atmosphere, history, and more.
- History
While the Earth was in its earliest stage (Early Earth), a...
- Earth's rotation
Earth's rotation or Earth's spin is the rotation of planet...
- Internal structure
Geological cross section of Earth, showing the different...
- History
Learn about the natural history of Earth from its formation to the present day, covering geological and biological events, time scales, and eons. Explore the evidence of life, evolution, extinction, and climate change on Earth.
Learn about Earth, the third planet from the Sun and the only one with life. Find out about its orbit, rotation, surface, atmosphere, history, and more.
- History
- Periods
- Changes
- Origin
- External Links
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Among the ancient Greeks, several of the Pythagorean school believed in the rotation of Earth rather than the apparent diurnal rotation of the heavens. Perhaps the first was Philolaus (470–385 BCE), though his system was complicated, including a counter-earthrotating daily about a central fire. A more conventional picture was supported by Hicetas, ...
True solar day
Earth's rotation period relative to the Sun (solar noon to solar noon) is its true solar day or apparent solar day. It depends on Earth's orbital motion and is thus affected by changes in the eccentricity and inclination of Earth's orbit. Both vary over thousands of years, so the annual variation of the true solar day also varies. Generally, it is longer than the mean solar day during two periods of the year and shorter during another two.[n 2] The true solar day tends to be longer near perih...
Mean solar day
The average of the true solar day during the course of an entire year is the mean solar day, which contains 86,400 mean solar seconds. Currently, each of these seconds is slightly longer than an SI second because Earth's mean solar day is now slightly longer than it was during the 19th century due to tidal friction. The average length of the mean solar day since the introduction of the leap second in 1972 has been about 0 to 2 ms longer than 86,400 SI seconds. Random fluctuations due to core-...
Stellar and sidereal day
Earth's rotation period relative to the International Celestial Reference Frame, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86 164.098 903 691 seconds of mean solar time (UT1) (23h 56m 4.098903691s, 0.99726966323716 mean solar days).[n 3] Earth's rotation period relative to the precessing mean vernal equinox, named sidereal day, is 86164.09053083288 seconds of mean solar time (UT1) (23h 56m 4.09053083288s, 0.99726956632908 mean solar da...
In rotational axis
Earth's rotation axis moves with respect to the fixed stars (inertial space); the components of this motion are precession and nutation. It also moves with respect to Earth's crust; this is called polar motion. Precession is a rotation of Earth's rotation axis, caused primarily by external torques from the gravity of the Sun, Moon and other bodies. The polar motion is primarily due to free core nutation and the Chandler wobble.
Measurement
The primary monitoring of Earth's rotation is performed by very-long-baseline interferometry coordinated with the Global Positioning System, satellite laser ranging, and other satellite geodesy techniques. This provides an absolute reference for the determination of universal time, precession and nutation.The absolute value of Earth rotation including UT1 and nutation can be determined using space geodetic observations, such as very-long-baseline interferometry and lunar laser ranging, wherea...
Ancient observations
There are recorded observations of solar and lunar eclipses by Babylonian and Chinese astronomers beginning in the 8th century BCE, as well as from the medieval Islamic worldand elsewhere. These observations can be used to determine changes in Earth's rotation over the last 27 centuries, since the length of the day is a critical parameter in the calculation of the place and time of eclipses. A change in day length of milliseconds per century shows up as a change of hours and thousands of kilo...
Earth's original rotation was a vestige of the original angular momentum of the cloud of dust, rocks and gas that coalesced to form the Solar System. This primordial cloud was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements ejected by supernovas. As this interstellar dustis heterogeneous, any asymmetry during g...
Learn about the rotation of Earth around its own axis and how it affects the length of a day, the seasons, and the orientation of the poles. Explore the history of the idea of Earth's rotation and its challenges and evidence from ancient to modern times.
Learn about the layers and properties of Earth's interior, from the crust and lithosphere to the core and mantle. Find out how scientists use various methods to study the chemical composition, density, and magnetic field of Earth.
Learn about Earth's features, history, and potential for life from NASA's science website. Find out how Earth differs from other planets in size, orbit, rotation, moon, rings, and formation.
Learn about the major geological events in Earth's past based on the geological time scale, from the formation of the Solar System to the present. Explore the Precambrian, the Phanerozoic and the ice ages, and see how Earth's surface and atmosphere evolved over billions of years.
