MOVEMENTS OF THE EARTH
Rotational motion
a movement that made the Earth spinning on itself along an ideal axis called Earth Axis passing through its poles. A complete turn, with reference to the stars, lasts 23 hours 56 minutes and 4 seconds and is called sidereal day . If we take the Sun the same meridian passes in front of our star every 24 hours, called solar day. 3 minutes and 56 seconds apart are because in that period of time the Earth has moved in its orbit and must turn more than a sidereal day to complete a solar day.
The first reference made by man was the Sun, whose apparent movement, originated in the Earth's rotation determines the day and night, giving the impression that the sky turns around the planet. In colloquial use language uses the word days to describe this phenomenon, which is astronomy referred to as solar day and corresponds to the solar time .
As shown in the chart, the earth's axis forms a angle of 23.5 ° to the ecliptic normal phenomenon called obliquity of the ecliptic . This tilt produces long months of daylight and darkness in the geographic poles, as well as being the cause of the seasons caused by the change of angle of incidence of solar radiation .
See also: Earth's axis , Day sidereal , Day and obliquity of the ecliptic
Consequences of rotation:
. Succession of days and nights.
. apparent movement of the stars . The sun and stars appear to move in the sky from east to west, but in fact the Earth rotates on itself in the opposite direction.
. deviation of falling bodies . bodies falling from heights are diverted to the east.
. deviation of the winds and ocean currents , right, in the northern hemisphere and counterclockwise in the southern hemisphere.
. polar flattening. When the Earth was not yet solidified, the simultaneous action of centrifugal and centripetal forces generated by rotation, produced the polar flattening and widening equator.
. difference of hours instead of different length . land for this movement is present, in the course of the day, all meridies against the sun. That is the solar noon at 12 o'clock local time, but that presents inconvenuente nearby places of different lengths have different local time. To avoid that settled in the world time zones .
translational movement
Main article: Translating Earth
is a movement by which the Earth moves around the sun because of this movement is the action of gravity , originating changes, like the day, allow the measurement of time . Taking the Sun, is what is called the tropical year , time required to repeat the season. Lasts 365 days, 5 hours and 47 minutes. The movement described is an elliptical path 930 million kilometers, at an average distance of the Sun from virtually 150 million kilometers, or 1 AU (Astronomical Unit : 149 675 000 km). It follows that the Earth moves with an average speed of 106 200 km / h (29.5 km / s).
The path or orbit is elliptical . The Sun occupies one focus of the ellipse and, due to eccentricity of the orbit, the distance between the Sun and Earth varies throughout the year. In early January, the maximum is reached near the Sun, producing the perihelion, where the distance is 147.5 million km, [ a ] , while in the first days of July is almost the maximum distance, called aphelion , where the distance is 152.6 million km.
See also: Tropical Year , Perihelion, Aphelion and Kepler
Consequences of translational motion
The tilt of the Earth's spin also gives rise to the succession of the seasons. Seasonal changes are most pronounced in the middle latitudes and are always complementary to each of the hemispheres of the Earth. For example, while in Spain it is winter, it is summer in Chile and vice versa. These contrasts are not due to the Earth is more or less from the Sun, but because the translation of our planet causes throughout the year to reach sunlight each hemisphere with different inclination with the time of year.
precesses
precession movement, also called the precession of the equinoxes is because the Earth is not spherical but an ellipsoid flattened at the poles. If the Earth were perfectly spherical, would make only the movements described above.
One complete turn of precession lasts 25 767 years cycle called Platonic year , whose duration was estimated by the former Maya. CONSEQUENCES
precession
The precession of the equinoxes is the movement of north celestial pole, which describes a full circle around the north pole of the ecliptic with a period of 25 780 years (the period known as Platonic year). This movement is due to precession movement of the Earth caused by torque exerted by the sun on Earth.
Hipparchus (second century BC ) was the first to give the value of the precession of the Earth with a unique approach for the time.
[] wobble
Main article: Nutation
movement is also due to the flattening of the poles and the attraction of the Moon on the equatorial axis. Also in a sawing motion occurs during the movement of precession, This in turn runs a small ellipse (like a small vibration.) One way around the ellipse represent 18.6 years, which means that one complete revolution of Earth's precession loops have completed 1385.
nutation RESULT
Nutation movement was because the moon's orbit is inclined to the plane of the orbit of the Earth . This causes disturbances in the Earth's axis direction, resulting in small wavelets during the precession.
movement nutation cycles in 18 years and reaching amplitudes are very small. This makes it an imperceptible movement for all people except for astronomers
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