General characteristics of our planet, and the two movements (rotation and revolution)

1. The Earth, our planet

2. What is the shape of the Earth?
• The Earth is not a perfect sphere. It is a geoid (an
imperfect sphere).

3. The Earth is divided into two hemispheres
A hemisphere is each of the two halves (*) planet Earth is divided
(*) Half: singular
Halves: plural

4. Life on Earth
• As far as we know, the Earth is the only planet in the Solar
System where life exists.
• Life is possible in our planet because:
- The temperature is ideal (not too hot, not too cold).
- The atmosphere has oxygen, and protects the Earth.
- There is water.

5. The outer structure of the Earth
• The Earth consists of three
parts:
- The atmosphere: gases
that surround the Earth.
- The hydrosphere: all the
water on Earth (salt or fresh).
- The lithosphere: the solid
rocks of the continents and
submerged under the oceans and
the seas.
The biosphere is the area of the Earth where life exists.

6. The two movements of the
Earth: rotation and revolution.

7. The Earth is moving all the time.
It moves in two ways:
• Rotation: The Earth spins from West to East on an
imaginary axis that goes from the North Pole to the South
Pole.
Axis

8. It takes approximately 24 hours (one
day) to complete one rotation

9. What are the
consequences of the
Earth’s rotation?

10. Consequence 1: The change from day to night
What would happen
if the Earth did not
rotate? What do you
think?

11. -One half of the Earth would be always lit
by the Sun, and it would be very hot!
-The other half would be dark and cold all
the time! Life would not be possible.

12. Consequence 2: The apparent (=not real)
movement of the Sun on the horizon
The Sun is a fixed star. It does not really move. But
during the day, it seems to move!
However, this is an illusion! It is our planet which
moves, not the Sun!
The Sun seems to move because the Earth rotates.

13. The sun rises (or appears) in the East
(dawn, or sunrise).
And it sets (or disappears) in the West
(dusk, or sunset)

14. According to the position of the sun,
we can identify the cardinal points
In order to know
where we are, we can
use a compass

15. Consequence 3: The existence of 24 time zones
Each time zone is the equivalent to one hour.
We use the Greenwich Meridian (0º) as a reference.
For example: when it’s 1 pm in
Spain, it is 7 am in New York.
(-6 hours)
And in Tokyo, it is 8 pm (+7
hours)

16. Second movement of the Earth: revolution

17. Revolution is the movement of the
Earth around the Sun
• The Earth revolves around the Sun. This movement is called
revolution.
• How long does it take? 365 days and 6 hours (one year).
• As each year has 365 days, every four years we add a day to
the month of February. That year is a leap year.

18. How does the Earth revolve?
• The Earth follows an elliptical trajectory called the orbit.
orbit
The Earth covers a
distance of 930
million km at a
speed of
106,000 km/h

19. The Earth’s axis is tilted! (=inclined)
The inclination of the Earth’s axis has important
consequences

20. Because the Earth revolves, each hemisphere
receives more or less heat and light
depending on the position of the Earth.
The Earth revolves
anticlockwise

21. There are two solstices: Winter (or December)
solstice, and Summer (or June) solstice.
In this position, the
Northern hemisphere
receives less light: it is
winter
The Southern
hemisphere receives
more light: it is
Summer
In this position,
the Northern
hemisphere
receives more
light: Summer
The Southern
hemisphere
receives less
light: Winter

22. The Equinoxes On March 21st, the day in
the Northern and the
Southern hemisphere have
the same length (12 hours)
On Sept. 23rd, the
day in the Northern
and the Southern
hemisphere have the
same length, too
Spring begins in
the North
Autumn begins
in the South
Autumn begins
in the North
Spring begins
in the South

23. Also, because of revolution and the
inclination of the axis…
the duration of day and night is different during the year
Here, days are longer
in the Northern
Hemisphere
Here, days are longer
in the Southern
Hemisphere