THE EARTH'S MOVEMENTS: Rotation and Revolution.

The Earth is not still in space, it is moving around itself (rotation) and and around the Sun (revolution or translation). This two movements have important consequences for life in Earth.

The rotation of the Earth.
Definition: The rotation of the Earth is the turning of the Earth around its imaginary axis, from west to east.
The length of this movement is about 24 hours.
This movement has important consequences:

• Alternation of day and night. As a consequence of this movement the Sun gives light and warmth to one side of the Earth, while the other side of the Earth remains in darkness and cools down.

• The apparent movement of the Sun. As a consequence of the rotation of the Earth from West to East, the Sun "appears" from the East and "disappears from the West. The name of the apparition of the Sun over the horizon is dawn, whereas the name of its dessaparition is dusk. Remember: it is the Earth that it is moving not the Sun.
• Geographic coordinates. The Earth's rotation allow us to identify the cardinal points and locate the position of any point in Earth.
• The division of the day in 24 hous and the establishment of time zones:

1. The Earth takes 24 hours to rotate completely, because of that we can divide the 360º of the Earth's sphere into 24 time zones that have a separation of 15º. Every place that is situated in the same time zone has the same solar time. 
2. In order to calculate the hour in a time zone we take as a reference the Meridian 0 or Greenwich meridian. We put the clock forward one hour for every time zone we move toward the East and we put the clock back one hour for every time zone we move towards the west from the Meridian 0.

For example, we want to know what time is it in the point B, if in the point A (located near the Greenwich Meridian) is the 12 o'clock. The point B is located at the east of the Greenwich Meridian and there is a difference of five time zones, because of this we have to add five hours and in the point B the time is going to be the 17:00.
In the same way, the point C is located at the west of the Greenwich Meridian and there is a difference of five time zones, because of that we have to extract seven hours and in the point C, the hour is going to be the 5:00.

The translation of the Earth (orbit).

Definition: The translation is the movement of the Earth around the Sun, from West to East.
Video: Earth orbit.
The length of this movement is about 365 days, 6 hours and 9 minutes, because of that every four years we have a year of 366 days (leap year).
This movement also has important consequences:

• The aparition of the Seasons of the year.
• The different duration of days and nights. During the summer the Norhtern Hemisphere is facing the Sun. As a consequence the illuminated area is bigger than the dark area and days are longer than nights. On the other hand, during the winter the Northern Hemisphere is no facing the Sun, as a consequence the illumanted area is smoller than the dark are an nights are longer than days.

 

• The apparition of different climate zones. Depending on the latitude, the Sun's rays fall with a different inclination. As a consequence Earth is divided in several climate zones:

1. One warm zone.
2. Two temperate zones.
3. Two cold zones.

Activity: 

Try to calculate the time in the points marked in the map, if in the time zone of the Greenwich meridian is the 12'oclock.