viernes, 28 de abril de 2017

The Earth

Know the Earth

The Earth is the fifth largest planet in the solar system and is the largest of the four terrestrial planets, formed about 4550 million years ago.

Know her friends

The Sun is the largest star located in the center of the solar system, but it is not the largest in the universe. The sun is the energy source of solar radiation that comes as light to Earth in 8 minutes and 19 seconds or 8.32 light minutes, This time is equivalent to the distance of 149 597 871 km that exists between the Earth and the sun. This energy allows the existence of life, through the process of photosynthesis performed by plants, algae and some bacteria, and conditions climatic and weather processes.
The moon, her only satellite, formed about 4530 million years ago, produces tides, stabilizes the tilt of its axis and gradually reduces the speed of rotation.

Where is the Earth located?

The Earth is spinning around its star, the sun, in the third orbit of the solar system; this system in turn is in the arm of Orion, one of the spirals that are concentrated within the gigantic milky way.

The Earth is round?

No, since if we imagine the Earth without water, it would look like a mass of rock that envelops its core presenting deviations on its surface, such as mountain ranges, abysses, volcanoes, etc. And if we fit this mass together with its mass of water into a sphere, it would fit perfectly into an oblate spheroid, idealizing the shape of the Earth as that of a sphere flattened at the poles, an approximation very close to its true form.

By this flattening is that it presents a bulge in the equator being 43 km of diameter longer than the diameter that exists between the two poles. In the equator its radius is 6371 km.

Earth Movements

Rotatory motion

Movement in which the Earth keeps rotating on its same imaginary axis (terrestrial axis) that passes through its poles. A complete return, taking as a reference to the stars, lasts 23 hours with 56 minutes 4 seconds and is called sidereal day; And taking as reference to the Sun, lasts 24 hours, called solar day. The 3 minutes and 56 seconds difference is the time it takes to advance in its orbit.

Translation movement

Movement in which the planet Earth rotates in an orbit around the sun, within a year, which is when the sun returns to its point of origin on the ecliptic.

The trajectory throughout its orbit is 930 million kilometers, at an average distance from the sun of 149 597 871 km (almost 150 000 000 km). The translation speed is about 106 200 km / h (29.5 km / s). The cause of this movement is the action of gravity, and causes a series of changes that, like the day, allow the measurement of time.
Two equivalent time periods are considered:
  • A tropical year, referring to the sun, which is the precise time to increase the average length of the Sun by 360 degrees above the ecliptic; that is to say, in completing one lap.

    Due to the precession of the equinoxes and to nutation, this time is different from that between two successive steps of the Sun by the so-called first point of Aries and by the spring equinox; its duration is 365.256363 solar days which is equal to 365 days 6 hours 9 minutes 9.7632 seconds.
  • A sidereal year, taken as a reference to the stars, is the time that elapses between two consecutive steps of the Earth by a same point of its orbit, since the sun is in a determined point of the sky with respect to the stars, until it returns to the same point again. Its duration is 365.255936 sidereal days.

The inclination of its axis, which is 23.4 ° with respect to the perpendicular of its orbital plane, a phenomenon known as obliquity of the ecliptic, makes the day and night prolongs for months at the poles, produces the seasons, which are different between the northern hemisphere and the southern hemisphere, thanks to the angle of incidence of solar radiation. The line that divides both hemispheres is the equator.

The more than 6 additional hours to the 365 days accumulate each year, after 4 years, it becomes 24 hours (1 day). Every four years there is a year that has 366 days, which is called a leap year.

Precession movement

The precession of the equinoxes is due to the precession movement of the Earth caused by the moment of force exerted by the Earth-Sun system as a function of the inclination of the Earth's rotation axis relative to the sun, about 23.43 ° and varies up to 27 ° thanks to natural phenomena. That is why the duration of a complete round of precession is never exact; nevertheless it is estimated that it is within an approximate range of between 25 700 and 25 900 years, denominated platonic year.

Nutation movement

Movement of oscillation of the axis of rotation downwards and upwards and accompanying that of precession.

This movement happens with any symmetrical or spheroid body rotating on its axis; like spinning, that after turning and before falling, the spike of the top rests on the ground with more force, so that increases the force of vertical reaction, that finally will become greater than the weight. When this happens, the center of mass of the spin begins to accelerate upwards. The process is repeated, and thus the movement is composed of a precession and a nutation.

For the case of the Earth, nutation is the periodic oscillation of the Earth's pole around its middle position in the celestial sphere, due to the external forces of gravitational attraction between the moon and the sun with the Earth.

Earth moves about 9 arc seconds every 18.6 years, and in a full precession round, Earth will have made 1385 loops.

Chandler wobble (Seth Carlo Chandler - 1891)

Almost imperceptible oscillation movement of the axis of rotation of the Earth that adds 0.7 seconds of arc in a period of 433 days to the precession of the equinoxes. They could be caused by climatic fluctuations that cause changes in the distribution of atmospheric mass, possible geophysical movements under the Earth's crust, variations in salt concentration in the sea, etc. Chandler Wobble together with these effects is called polar movement or variation of latitude, considered unpredictable in the long term. The Earth's poles move in an irregular circumference of 3 to 15 meters in diameter, in an oscillatory movement. This is an addition to the precession of the equinoxes, a greater oscillation that needs about 26,000 years to complete.

Structure of the Earth

The internal structure of the Earth, like that of other terrestrial planets (planets whose volume is mainly occupied by rocky material), is divided into layers of increasing density. The Earth has an outer shell of solidified silicates, a viscous mantle, and a core with two other layers, an outer solid, much more fluid than the mantle, and a solid inner. Many of the rocks that now form part of the crust were formed less than 100 million (1 × 108) years ago, during the Cretaceous period. However, the oldest known mineral formations have 4.4 billion (4.4 × 109) years, which indicates that at least the planet has had a solid crust since then.

The structure of the Earth could be established according to two different criteria. According to its chemical composition, the planet can be divided into bark, mantle and core (external and internal); According to their physical properties the lithosphere, the asthenosphere, the mesosphere and the nucleus (external and internal) are defined.

The division of the Earth into layers has been determined indirectly using the time it takes to travel the reflected and refracted seismic waves created by Earthquakes. The transverse (S, or secondary) waves can’t traverse the core, since they need a viscous or elastic material to propagate, whereas the propagation velocity is different in the other layers. Changes in velocity produce a refraction due to Snell's Law. Reflections are caused by a large increase in seismic velocity (propagation velocity) and are similar to reflected light in a mirror.

Live on the Earth

During a long process of geological and climatic changes, the atmosphere of the Earth was adapting the appropriate conditions for life, pioneering aquatic anaerobic microorganisms such as bacteria and archaea, and then, 3500 million years ago, the first beings Photosynthetics, cyanobacteria gave rise to the oxygenation of the atmosphere that generated the ozone layer 2400 million years ago and which led to the proliferation of aerobic microorganisms, which evolved into much more complex organisms and colonized the Earth's surface, finding life in both the sea, on Earth and in the air.

According to James Lovelock, the Earth is a living being where the atmosphere and the superficial part of planet Earth behave as a coherent whole where life, is responsible for regulating its essential conditions such as temperature, chemical composition and salinity in the case of the oceans. It is a self-regulating system, which fosters and maintains adequate conditions for itself. (Gaia Hypothesis).


1863, De Miranda A. Enciclopedia popular: Manual de Astronomía popular. ed rev. Hispano-Americana. Madrid. ES. 334p. Pag 324, 325.