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The Earth is subject to movements of various kinds. The main movements of the Earth" are defined with reference to the Sun and are: [Earth rotation | rotation]], [Translation of the Earth | translation]], precession, nutation, Chandler Wobble and perihelion precession.

Rotational movement

Main article: Earth's Rotation

Rotation movement.

It is a movement that the Earth performs by rotating on the Terrestial axis, which intersects the surface at two points called poles. This rotation is from west to east, meaning for an observer situated in space above the Earth's North Pole, this movement is Dextrorotation and Levorotation (counterclockwise). A complete rotation, taking the stars as reference, lasts 23 hours with 56 minutes 4.1 seconds and is called Sidereal day. If we take the Sun as a reference, the same meridian passes in front of our star every 24 hours, called solar day. The approximate 3 minutes and 56 seconds of difference are due to the fact that during that period-of-time, the Earth has progressed in its orbit and must rotate more than a sidereal day to complete a solar day.

The first reference point taken by humans was the Sun, whose apparent movement, originated in the rotation of the Earth which determines day and night, giving the impression that the sky rotates around the planet. In colloquial language, the word day is used to designate the period known in astronomy is called solar day, which corresponds to solar time

Translational Movement

It's the movement by which the planet Earth rotates in a elliptical orbit] around the Sun in 365 days and slightly less than 6 hours. For an observer located in space above the terrestrial North Pole, this movement is also Dextrorotation and Laevorotation (contrary to clockwise), and logically, seen from the terrestrial[[South] Pole], this movement is Dextrogyre (like the direction of the clock hands). As the calendar records 365 whole days, the beginning of each year advances, which is compensated for approximately by making one out of every slightly more than four years, known as a leap year, have 366 days. The cause of the translational movement is the action of gravity and generates a series of changes that, like the day, allow the measurement of time. Taking the Sun as a reference, it results in what is called a tropical year, the necessary period for the seasons of the year to repeat. Lasts 365 days, 5 hours, 48 ​​minutes, and 45 seconds. The movement it describes is an elliptical trajectory of 930 million kilometers, at an average distance from the Sun of nearly 150 million kilometers, 1 astronomical unit (astronomical unit: 149597871 km) or 8,317 light minutes. From this, Earth travels through its orbit at an average speed of 106,200 km\/h (29.5 km\/s).

The Earth's trajectory or orbit is elliptical. The Sun occupies one of the spotlights of the ellipse and, due to eccentricity of orbit, the distance between the Sun and the Earth varies throughout the year. In the first days of January, the maximum proximity to the Sun is reached, producing perihelion, when the distance is 147.5 million kilometers,<ref>Phillips, Tony «The Earth at Perihelion»' ' (2001). [http:\/\/ciencia.nasa.gov\/headlines\/y2001\/ast04jan_1.htm science nasa] Archived 2010-06-06 at the Wayback Machine}}}}}}}}}}}} <\/ ref> while in the first days of July the maximum remoteness is reached, called AFELIO, when the distance is 152.6 million kilometers.

As seen in the graph above, the Earth's axis forms an angle of about 23.5º relative to the normal of the ecliptic, a phenomenon called obliquity of the ecliptic. This inclination, combined with the Earth's orbit around the Sun, results in long periods of continuous months of continuous light and darkness at the geographic poles, as well as being the cause of the seasons, resulting from changes in the angle of incidence of solar radiation and the duration of daylight hours produced by that obliquity.

See also: Tropical year, Perihelion, Aphelion, and Kepler's Laws

File:Diagram of Earth's movements.png

Precession Movement of the Equinoxes

Main article: Precession

Precession angle.

The precession of the equinoxes (the slow and gradual change in the orientation of the Earth's rotation axis) is due to the precessional movement of the Earth caused by the torque exerted by the Earth-Sun system, depending on the inclination of the Earth's rotation axis with respect to the plane of the Earth's orbit (currently around 23°43'). This movement completes every 25, 776 years (so approximately every 130 [centuries] the seasons would reverse, but the difference between the sidereal year and the tropical year is incorporated and corrected by the Gregorian calendar) and an observer in space, situated over the North Pole, would see it as a turn dextrogyr (in a clockwise rotation).

The inclination of the earth's axis varies from 23 ° to 27 °, as it depends (among other causes) on the [Telluric movements]]. In February 2010, there was a variation in the Earth's axis of approximately 8 centimeters caused by the 8.8 ° earthquake Richter that affected Chile. While the tidal and consequent tsunami that hit the Southeast Asia in 2004, displaced 17.8 centimeters to the Earth's axis. Shortened Earth Days »(2010). [http:\/\/www.nasa.gov\/topics\/earth\/feathures\/earth-20100301.html nasa] . <\/ ref>

Nutation movement

Main article: Nutation

The precession is accompanied by an oscillation of the rotation axis upwards and downwards, which is called nutation.

The precession is even more complex if we consider a fourth movement: nutation. This happens with any symmetrical body or spheroid rotating on its axis; a spinning top (top) is a good example, because when it falls the precession begins. As a consequence of the falling movement, the tip of the spinning top is supported on the ground with more force, so the vertical reaction force increases, eventually becoming greater than the weight. When this happens, the center of mass of the spinning top begins to accelerate upwards. The process repeats itself, and the movement consists of a precession accompanied by an oscillation of the rotation axis up and down, which is called nutation.

In the case of the Earth, nutation is the periodic oscillation of the Earth's pole around its mean position on the celestial sphere, due to the external gravitational attraction forces between the Moon and the Sun with the Earth. This oscillation is similar to the movement of a spinning top (top) when it loses strength and is about to fall.<ref>Argüello, Luis (2003). «Mechanical». P. 190. <\/ ref>

The Earth shifts about nine arcseconds every 18.6 years, which means that in one complete precession cycle, the Earth will have completed 1,385 loops. To get an idea of this movement, let's imagine that while the axis of rotation describes the conical precession movement, it also traces a small ellipse or loop in a period of 18.6 years.

In a complete precession cycle (25,776 years) the Earth completes more than 1300 loops of nutation. The nutation movement of the Earth was discovered by the British astronomer James Bradley.

Chandler wobble

Main article: Chandler wobble

This is a small oscillation of Earth's rotation axis that adds 0.7 arcseconds over a period of 433 days to the [precession of the equinoxes]]. It was discovered by the American astronomer Seth Carlo Chandler in 1891, and currently, the causes that produce it are not known, although several theories have been proposed (climatic fluctuations causing changes in the distribution of atmospheric mass, possible geophysical movements beneath the Earth's crust, variations in salt concentration in the sea, etc.).<ref>Lambeck, K., 1980, The Earth's Variable Rotation: Geophysical Causes and Consequences, Cambridge University Press , London.<\/ref> The sum of the Chandler Wobble and other minor effects is called polar motion.

Precession movement of perihelion

Main article: Perihelion

Exaggerated artistic representation of apsidal precession

In the orbital motion, Earth describes an ellipse around the Sun, which occupies one of the foci of this ellipse, but the other focus is not static; it also rotates slowly by a small angle of 3 .84 arcseconds per century, around the Sun, in the same direction as the orbit. This rotation of the free focus of the ellipse is known as apsidal precession, precession, or advance of the perihelion, which is the moment of the Earth's closest approach to the Sun. Logically, the aphelion, or moment of the Earth's greatest distance from the Sun, also experiences this advance, which, although angularly equal, is even greater tangentially. This movement has a period of about 34,285,714 years.

Orbital variations

The orbital variations or Milankovitch cycles describe the combined effects of Earth's movements on the climate over thousands of years. The term was coined after studies conducted by the Serbian astronomer and geophysicist Milutin Milanković. In the 1920s, he theorized that the resulting variations caused cyclical changes in solar radiation reaching the Earth's surface, significantly influencing patterns of climate change on Earth.

Some similar astronomical theories had been anticipated during the 19th century by Joseph Adhemar, James Croll, and others. Still, their verification was complex due to the absence of relevant fossil data and because it was unclear which periods were important in the past to check.

Today, geological materials on Earth's surface that have remained unchanged for thousands of years are being studied by specialists to determine changes in Earth's climatology. Although many of them are consistent with the hypotheses of Milankovitch's theories, there is a set of them that predictable hypotheses cannot explain.

See also

• Land
• Orbital variations
• Kinematics of the rigid solid
• Polar movement

References

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Categories:

• Geophysics
• Earth