The land It is our planet and the only one inhabited. It is located in the ecosphere, a space that surrounds the Sun and has the right conditions for life to exist.
And he has it. It is now dominated by some primates that have evolved to study astronomy. The earth is Planet of the Apes.
Our Earth is the largest of the four rocky planets. Its size makes it possible to retain a layer of gases, the atmosphere, which disperses sunlight and absorbs heat. By day it prevents our planet from getting too hot and, at night, to cool down.
Seven out of ten parts of the earth's surface are covered with Water. The seas and oceans also help regulate the temperature. The water that evaporates forms clouds and falls in the form of rain or snow, forming rivers and lakes. At the poles, which receive little solar energy, the water freezes and forms the polar caps. The one in the south is bigger and concentrates the largest reserve of fresh water.
The following table shows some measurements of the Earth. In the last column, the order that each data occupies between the planets of the Solar System.
|Basic data||The earth||Order|
|Size: equatorial radius||6,371 km.||5º|
|Average distance to the Sun||149,597,870 km.||3º.|
|Day: period of rotation on the axis||23.93 hours||5º.|
|Year: orbit around the Sun||365,256 days||3º.|
|Average surface temperature||15 º C||7º.|
|Surface gravity in the equator||9.78 m / s2||5º.|
Earth is not a perfect sphere, but it has pear shape. Calculations based on disturbances of the orbits of artificial satellites reveal that 21 km is thickened on the equator; the north pole is dilated 10 m and the south pole is sunk about 31 meters.
It was formed about 4.6 billion years ago, along with the entire Solar System.
Although the rocks older than 4,000 million years, meteorites, which correspond geologically with the Earth's core, give dates of about 4.5 billion years. The crystallization of the nucleus and the meteorite precursor bodies is believed to have occurred at the same time, some 150 million years after the Earth formed along with the entire Solar System.
After condensing from cosmic dust and gas by gravitational attraction, the Earth was almost homogeneous and quite cold. But the continued contraction of materials and the radioactivity of some of the heaviest elements made it warm up.
Later it began to melt under the influence of gravity, producing the differentiation between Cortex, he mantle and the nucleus, with lighter silicates moving up to form the crust and mantle, and heavier elements, especially iron and nickel, falling towards the center of the Earth to form the nucleus.
At the same time, the eruption of the numerous volcanoes caused the release of volatile and light vapors and gases. Some were trapped by Earth's gravity and formed the primitive atmosphere, while condensed water vapor formed the first oceans.
Earth behaves like a huge magnet. The English physicist William Gilbert was the first to point out terrestrial magnetism in 1600, although its effects had been used much earlier in primitive compasses.
The Earth is surrounded by a powerful magnetic field, as if our planet had a huge magnet inside, whose south pole was near the geographical north pole and vice versa. By parallel with the geographical poles, the Earth's magnetic poles are called magnetic north pole and magnetic south pole, although its real magnetism is of opposite sign to which their names indicate.
The magnetic north pole is located today near the west coast of Bathurst Island in the Northwest Territories in Canada. The magnetic south pole is at the end of the Antarctic continent in Tierra Adelia.
The positions of the magnetic poles are not constant and show remarkable changes from year to year. Variations in the Earth's magnetic field include the change in the direction of the field caused by the displacement of the poles. This is a periodic variation that is repeated every 960 years. There is also a smaller annual variation.
Following the Astronomy course, the following pages delve deeper into the Earth, its structure, its movements and its only natural satellite, Moon. In addition, here we leave some links with more information, among them, a whole section dedicated to our planet and its satellite.
• Planet Earth HD 3D
• Earth and Moon Sciences (section, 90 pages)
• Episodes of "This is how Earth was made" on DPLAY
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