The earth

   1. The earth

   The Earth is one of the nine planets in the Solar System . In the olden days, some people thought that the Earth was flat but other people imagined it was square. Nowadays, we know that its shape is similar to an orange, that is, as a sphere with flattened poles. This form is called the geoid.

   In the upper picture, we see that a vessel gets away from the coast with a man and a lighthouse. At the begining the man hides out and later the lighthouse is no longer seen. This shows that the earth's surface is circular.

   2. Lines and circles of the globe

   To locate a particular point on the Earth's surface, It has been found that on the globe exist a number of imaginary points, lines and circles. These are:

   - The axis: it is the line where the Earth spins around. It runs from the North Pole to the South Pole and it is tilted with reference to the plane of the earth's orbit around the Sun.

   - The Equator: it is the great circle perpendicular to the earth's axis. It divides the earth into two equal parts called hemispheres: the northern or boreal hemisphere and the southern or austral hemisphere.

   - - The Meridians: they are semi-circles passing through the poles. They are vertical lines.

   - The parallels: they are circles parallel to the Equator . They have different sizes : the biggest are close to the Equator and the smallest are close to the Poles . The most important parallels are four: the Tropic of Cancer and the Arctic Circle in the northern hemisphere and the Tropic of Capricorn and the Antarctic circle in the Southern Hemisphere.

   3. Answer with one of the imaginary lines: axis, Equator, meridian or parallel:

The Arctic Circle

The line between the North Pole and the South pole

The Tropic of Cancer

What form the hemispheres

The Antarctic Circle

The Semi circle passing through the poles

The Tropic of Capricorn

   4. Earth's movements: Earth's Rotation
   At first sight, it seems that the earth does not move, but it really has two movements: the earth's rotation and the earth's orbit.
   The Earth rotates around the axis every 24 hours.
   As we see in the picture, while the rays of the sun reach only half of the Earth's surface producing the day, in the other half occurs the night.
   The time difference is another consequence of the earth's rotation. As the movement is from west to east, the Sun appears sooner in places situated to the east, where the day starts early. The Earth is divided into 24 sections called time zones. Europe comprises three time zones: the Western, Central and Eastern Europe. Spain belongs to the first. When we go from one time zone to another, the clock must set one hour forward or backward. Check this presentation presentación

   5. Indicate if these sentences are true or false:

The Earth does not move

The Earth rotates around the axis every 24 hours

It is day when the rays of the sun do not reach the Earth's surface

The Earth rotates from west to east

There are 28 time zones

The Sun appears sooner in the east

   6. Earth's orbit
   The Earth revolves around the sun in an elliptical orbit, and this orbit lies in a specific plane called the ecliptic. It takes 365 days and a little more, that is, one year. To correct the difference, it is added one day every four years. It is known as the leap year with 29 days in February.
   The Earth's orbit has two consequences:
   - The inequality of days and nights. This is because the equatorial plane does not coincide with the ecliptic plane. In the northern hemisphere, the days are longer in summer than in winter and nights are shorter than days. In the Equator, the days are equal to the nights.
   - The seasons are four:
   Spring: it goes from March 21 to June 21.
   Summer: it goes from June 21 to September 23.
   Autumn: it goes from 23 September to 22 December.
   Winter: it goes from December 22 to March 21.
 There are two days a year when the days and nights are of equal duration: the equinox. March 21 is the spring equinox and September 22 is the autumnal equinox.
   There are also two days that are totally unequal: The longest Day (June 21) is the summer solstice and the shortest day (December 22) is the winter solstice.

   7. Indicate if these sentences are true or false:

The leap year has 365 days

The orbit of the Earth is called Ecliptic

In the Equator, the days and nights are equal

Spring goes from March to December

Summer goes from June to September

Equinox: equal days and nights

The spring equinox is in September

Solstice: unequal days and nights

The shortest day is in June

   8. Climate Zones
   The amount of heat that receives the Earth's surface varies according to the inclination of the surface with respect to the rays of sunlight. We distinguish the following zone:

   - Torrid or tropical zone, between the Tropic of Cancer and the Tropic of Capricorn. Temperatures are high.

   - Temperate zones between the tropics and the polar circles, one in the northern hemisphere and the other in the southern hemisphere. The temperature is lower.

   - Frigid or polar zones between the polar circles and the poles. It is very cold.

    9. The orientation

   To orient ourselves, we must find the four cardinal directions: North (N), South (S), East (E) and West (W). The intermediate points are: Northeast (NE), Northwest (NW), Southeast (SE) and Southwest (SW).

   There are several ways to orient ourselves:

  a) The Sun rises in the east and sets in the west. As we see in the picture, if we put the right arm where the sun rises, we will find the East. The left arm will indicate the West, the North will be forward and the South will be behind.

   b) The compass is an instrument that always indicates the north.

   c) At night, the Polar Star shows us the North.


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