SESSION 4. THE EARTH'S ORBITING AROUND THE SUN

UNIT 1. PLANET EARTH

SESSION 4. THE EARTH IN MOTION

The  Earth’s orbiting around the Sun and its consequences

·         You have to Know…

Translation movement

It is the Earth’s movement 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 translation movement causes the four seasons.

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.

The change of seasons

Seasons 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.	Summer solstice
During the Summer solstice (June 21), in the Northern hemisphere is Summer and in the south is Winter. 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.

·         Aditional information

The existence of thermal zones:

·         Vocabulary

-          Equinoxes: when day and night are of equal length.

-          Solstices: the time of year when there is the greatest length of daylight (summer solstice) or the shortest (winter solstice)

-          Tropical: two imaginary circles running round the earth at about 23 degrees north ( Tropic of Cancer) or south ( Tropic of Capricorn) of the equator

-          Temperate: neither too hot nor too cold

-          Frigid: very cold.

-          Equator: an imaginary line (or one drawn on a map etc) passing round the globe, at an equal distance from the North and South pole

-          Season: one of the main divisions of the year according to the regular variation of the weather, length of day etc. There are four seasons: autumn. winter, spring and summer.

-          Demarcate: to show the limits of something

-          Length: the distance from one end to the other of an object, period of time etc

-          To find out: To discover or investigate something.

·         Exercises

1.    Write down the names of the Earth’s thermal zones, and the limits that demarcate them.

2.    Are the following statements true (T) or false (F)? Correct the false ones.

-          When one of the Earth’s hemispheres is turned away from the Sun, it is spring or autumn. (   )

-          At the solstices, day and night are of equal length in each hemisphere (   )

-          There are five seasons along the year (   )

-          The equator is in the frigid zone of the Earth (    )

3.    Why when it is summer in the northern hemisphere is winter in the southern?

·         Investigator’s corner

1.     Find out how many Kilometers per second the Earth travels during its revolution around the Sun, and how many kilometers it travels a day?