THE EARTH
A.- WHAT IS IT?

  • A planet

The Earth is one of the planets of the solar system. It ranks third in proximity to the sun, which receives light and heat.It is approximately 150 millions of kilometres far from the sun.

  • Water and land

Most of its surface is water (75%) and its divided between oceans, seas, rivers and lakes. The remaining 25% is land distributed between continents and islands. The Earth colour seen from the space is blue, due to the sea water.

external image surfacedistribution.gif

  • Spherical in shape

The Earth planet is spherical in shape, but not perfect, as it is flattened by the poles.


An imaginary perpendicular line to the axis of the Earth, the Equator, divides it into two hemispheres: North and South.

  • An alive planet

The Earth is the only planet of the solar system where life exists. This is possible due to a number of factors:

  • Temperature: the Earth is far from the sun 150 million km, which allows life. external image -solarradiation.gif
  • Atmosphere: covers the Earth from pernicious solar radiation, protecting it and allowing life on it.
  • Liquid water: essential for plants and animals.


B.- MOVEMENTS OF THE EARTH



The earth is not static, it moves steadily through space, following two movements:*ROTATION
external image earthplanet.gif
It is the one which describes the Earth spinning around an imaginary axis, eastbound.The axis of rotation is tilted with respect to the plane of the orbit that describes the Earth around the sun.The day, the night and the hours**The rotary motion produces a succession of day and night, as well as the time difference between some areas of the Earth.As the Earth is spherical it is only illuminated on the face opposite to the sun. As it is turning on itself, the lighted face is not always the same. So the illuminated part (day) and the dark part (night) are constantly shifting.external image timezones.jpgConsequences of the rotation movement:
  • Day and the night
  • A uniform insolation of the Earth

***TRASLATION
It is the one that the Earth accomplishes around the Sun. It describes an elliptical orbit of 93 million km, maintaining a speed of 29.8 km / seconds
A year
  • In this tour the Earth spends 365 days and 6 hours. Those 6 hours which are accumulated each year, after 4 years, they are 24 (one day). Each four years there is one that has 366 days, called leap year.
  • The plane that determines the Earth's orbit is called the ecliptic circle and is the maximum that the Earth describes in its movement around the Sun.
The seasons
  • The traslation movement causes the four seasons.
The change of seasonsSeasons are changing alternately by the hemisphere which is closer to the sun. When the northern hemisphere is the farthest from the sun, it will be winter, while simultaneously, the southern hemisphere is closer and then it is summer there.There are 4 key positions in the movement of translation: Spring and Autumn (equinoxes) and Summer and Winter (solstices).
  • During the Spring equinox (March 21), in the northern hemisphere is Spring and in the Southern Hemisphere is Autumn.
  • During the Autumn equinox (Sept. 23), in the northern hemisphere is Autumn and in the Southern Hemisphere is Spring.
  • During the Winter solstice (Dec. 22) in the northern hemisphere is winter and in the south is Summer.

  • The stations are determined by the tilt of the earth's axis on the ecliptic. According to the position of the sun-earth connection, some areas receive more solar radiation than others.
  • Another effect of the inclination of the axis of the Earth on the ecliptic is the different duration of the day and the night, as Summer or Winter.
  • During the Summer solstice (June 21), in the Northern hemisphere is Summer and in the south is Winter.