UNIT 1. PLANET EARTH

1. THE EARTH AND THE UNIVERSE. 

1. 1. The universe.

The universe appeared 14 billion years ago with the “Big Bang”, the explosion of a small mass which contained all the existing matter and energy.
The universe contains:
•       Stars, huge balls of gas which produces its own light and heat.
•       celestial bodies:
Ø  planets, a celestial body which rotates around a star and does not produces its own light and heat.
Ø  satellites, a celestial body which rotates around a planet.
•    Comets, a celestial body made of ice and dust and with a tail of gas.
•    Asteroid, a small celestial body made of rock.

1. 2. The Milky Way.

•    A galaxy is a group of millions or billions of stars.
•    In the universe, there are millions galaxies.
•    One of them is the Milky Way, in which the Solar System is located.
•    The Milky Way is part of a group of 20 galaxies called the Local Group.
•    The Milky Way is spiral shaped. The solar system is located in one of its arms. 

1. 3. The Solar System.

The Solar System is the planetary system to which the Earth Belongs.

It consists of eight planets and another celestial bodies (asteroids, satellites and comets) which move around a star of average size, the Sun.

2. 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.

2. 1. 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. 

Consequences:

• Alteration of day and night.

The Sun gives light and warm to one side of the Earth, while the other side of the side of the Earth remains in darness and cools down.

• The apparent movement of the Sun.

It is the Earth that it is moving, not the Sun
Dawn: The Sun “appears” in the East”.
Dusk: The Sun “disappears in the West”.

• Apparition of the time zones.

The Earth takes 24 hours to rotate completely, because of this we can divide Earth into 24 time zones.
A time zone is one of the 24 divisions of the Earth's globe which have the same solar time.
What time is it in another time zone?

We put the clock forward one hour for every time zone we move towards the east
We put the clock back one hour for every time zone we move towards the west 

   2. 2. The translation of the Earth (orbit).

Definition: The translation is the movement of the Earth around the Sun, from West to East.

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 Northern 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 illuminated area is smaller 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.

3. THE SEASONS: Solstices and equinoxes.

The Earth's axis is gently inclined (about 23º) but always points in the same direction (in the direction of the Polar Star, because of that the Axis orientation do not change even though the Earth is rotantig around the Sun but its position in relation to the Sun does.

3. 1. The seasons of the year.

As a consequence of the orbit of the Earth, during different moments of the year the quantity of light and heat that the different parts of the Earth receive from the Sun is going to change :

During summer and winter, the rays of Sun falls directly on one hemisphere while the other receives them with a strong inclination, making it winter. Nevertheless, during spring and autumn, the rays fall on both hemispheres with the same inclination.

When the rays of the Sun are inclined, the same amount of heat is projected onto a larger area, and there is less concentration of heat.

3. 2. Equinox and solstice.

Equinox: is the time of the year when the Sun's rays falls perpendicular to the Equator. The Sun iluminates the North Pole and the South Pole for the same number of hours. There are two equinox:

• The spring equinox (March 21), it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
• The autumn equinox (September 21). it is autum in the Southern Hemisphere and spring in the Southern Hemisphere.

Solstice: is the time of the year when the Sun's rays fall perpendicular to one of the tropics. There are two solstices:

• The Summer solstice (June 21): the Sun is facing the Tropic of Cancer. It is summer in the Northern Hemisphere and winter in the Southern Hemisphere.
• The Winter solstice (december 21): the Sun is facing the Tropic of Capricorn. It is summer in the Southern Hemisphere and winter in the Northern Hemisphere.

Video about the Earth's rotation and revolution:

Video about the Seasons:

4. Planet Earth: shape and dimensions.

The Egyptians were the first to try to determine the shape and size of the Earth.
The Greeks established the first scientific theories about its shape and size.
Today, artificial satellites allow us to obtain a very detailed information about Earth's size and size.

4. 1. The shape of Earth.

Is not a perfect sphere, because It is slightly flattened at the poles (geoid).
We can divide the earth into two hemispheres: one of the two halves into which we can divide the Earth.
Northern Hemisphere or continental hemisphere, because contains more land.
Southern Hemisphere or maritime hemisphere, because it is mostly made up of oceans.
71% of the Eearth is covered by water.

4. 2. The size of the Earth.

The equatorial circunference of the Earth is about 40.070 km.
The polar diameter is 12.756 km.
The equatorial diameter 12.714 km.

5. THE GEOGRAPHIC GRID: LATITUDE AND LONGITUDE.

4. 1. The geographic grid.

The Geographic grid is the system of coordinates that we use in order to locate any point in the Earth’s surface.
Both extremes of the Earth´s axis are connected to two fixed points: the poles
From these points we trace imaginary lines that cross with others to form a grid.

4. 2. Parallels and meridians.

This system is based in two types of imaginary lines: parallels and meridians:

Parallels: Imaginary lines that encircle the Earth, perpendicular to its axis.

The main parallel is the Equator which divides the Earth into two halves. Another important parallels are the Tropic of Cancer, located in the Northern Hemisphere and the Tropic of Capricorn, located in the Southern Hemisphere.

Meridians: Imaginary semicircles traced from pole to pole.

The most important meridian is the meridian 0º or Greenwich meridian, which runs through Greenwich, near London.

4. 3. Latitude and longitude.

We use this imaginary lines in order to establish the latitude and the longitude of a point located in the Earth’s surface.

Latitude: The distance, measured in degrees, from any given point to parallel oº or the equator. The maximum latitude is 90º and can be either north or south.

Longitude: The distance, measured in degrees, from any given point to meridian 0º or Greenwich

The maximum longitude is 180º and can be either east or west.

Remember: every degree (º) can be divided into 60 minutes (') and every minute can be divided into 60 seconds (''), the same way than an a hour. For example, the geographic coordinates of the IES Cervantes High School are: 40º 24' and 12" N and 3º 42' 8" W.

5. Representing the Earth.

It is imposible to translate a sphere into a flat Surface. 
The best way to represent the Earth is a Earth globe, but for practical reason sometimes we need representations of the Earth in a flat surface, like a planisphere.

Earth globe.

Planisphere

5. 1. Maps and projections.

A map is a simplified representation of the spherical surface of the Earth, or a par of it, on a flat surface. In order to make a map we need three things:

• a system of projection.
• a scale
• a key.

5. 2. System of projection.

 A system of projection is one of the different ways that allow us to represent a spherical surface in a flat surface with as little distorsion as possible. . A projection can meet  two or three conditions necessary to have a  but never the three at the same time:

• Conformal: preserving correct shapes.
• Equidistant: preserving correct distances.
• Equivalent: preserving correct sizes.

The most important systems of projection three are:

• Cylindrical projection projects the grid of parallels and meridians into a cylinder. It is the best method to represent the low latitudes between the equator and the tropics.
• Conical projection projects the grid of parallels and meridians into a cone, which touch the Earth in one parallel.The most appropriate to represent the mid-latitudes.
  
•  Flat projection projects the grid of parallels and meridians into a plane. It is the best way to represent the poles or one hemisphere. 

5. 3. Scale.

The scale is the method that we use to indicate the relation between a distance drawn on the map and the same distance on the ground. There are two types of scale:

• Numeric scale, use a fraction. The numerator indicates the distance on a map and the denominator its equivalent on the ground. 

•  Graphic scale. It consists of a straigh line divided into segments. Every segment is equivalent to a real distance in the ground.

• Legend or key of the map: is a set of colours, standar signs or symbols used to represent reality in the map in a simplified form.

An example of map key.

 ACTIVITIES.

1. Indicate the latitude and the longitude of the letters that appear in the following map.

2. Write down the concepts that correspond to the definitions in the table.

UNIT 1. THE EATRH AND ITS REPRESENTATION

With an A	The envelope of gases surrounding the Earth.
With a C	A system of projection that translates the meridians and parallels onto a cone. It is the most appropriate way to represent the mod-latitudes, between the tropics and the polar circles.
With a C	A projection system that translate the parallels and meridians onto a cylinder. It is the best method to represent the low latitudes between the equator and the tropics.
With a D	The time each morning at which daylight first begins. Sunrise.
With an E	A line notionally drawn on the earth equidistant from the poles, dividing the earth into northern and southern hemispheres and constituting the parallel of latitude 0.
Contains an F	The different shapes that the surface of the Earth has adopted over millions of year, as a result of internal forces.
With a G	A coordinate system that allows us to find every location on the Earth by its latitude and longitude.
With a G	A scale that use a graduated ruler to indicate the equivalent to ground distance.
With a H	Half of the earth, usually as divided into northern and southern halves by the equator, or into western and eastern halves by an imaginary line passing through the poles.
Contains an I	The time of year when the Sun´s rays fall perpendicular to one of tropics. A 24-hour night takes place in one of the poles while the other has a 24-hours day.
Contains  a K	The darker stage of twilight, especially in the evening. To become or make dark or dusky.
With an L	The distance, measured in degrees, from any given point to parallel 0º or the equator.
With an L	A year, occurring once every four years, which has 366 days including 29 February as an intercalary day. It is due to the orbit movement.
With a M	A representation of the spherical surface of the Earth, or a part of it, on a flat surface.
With an M	Imaginary semicircles traced from pole to pole. We use them to measure the longitude.
With an N	A scale that use a fraction to indicate the equivalent to ground distance. The numerator designates the distance on the map, and the denominator tells us its equivalent on the ground.
With an O	The movement of the Earth around the sun.
With a P	A celestial body moving in an elliptical orbit around a star.
With a P	A projection system that translates the meridians and parallels onto a plane that touches the Earth on one of the poles. It is the most appropriate method to represent the polar areas.
With a P	Imaginary lines that encircle the Earth, perpendicular to its axis. We use them to measure the latitude.
With an R	The turning of the Earth around its imaginary axis.
With an S	The number or graphic that indicates the relation between a distance drawn on the map and the same distance on the ground.
With a T	Any of the 24 longitudinal divisions of the earth's surface in which a standard time is kept.
With a T	A type of map that represents in detail the physical and human aspects of the territory: relief, water, flora, communication routes, land use etc.
With a T	A type of map that represents a specific geographical aspect such as climate, relief, population, etc.
Contains a  U	A distance, measured in degrees, from any given point to meridian 0º or Greenwich.
Contains an X	The time of year when the Sun´s rays fall perpendicular to the equator. The Sun illuminates the North Pole and the South Pole for the same number of hours.
Contains a Y	A sun with planets, asteroids, comets, etc. in orbit around it.

  

You can find the solutions here .