The Earth, like the rest of the planets in the Solar System, moves around the Sun. It also moves on its own axis.
The Sun is not located in the middle of ellipse because the distance between the Earth and the Sun varies as it moves along its orbit.
Because takes a little more than 365 days to complete its revolution (almost a quarter of a day more), we have to add a day to the month of February every 4 years. This is called a leap year.
Characteristics of the Earth's revolution cause the amount and intensity of sunlight that hits a part of the Earth to vary during the year.
These variations cause the seasons.
During the summer, the sun's rays hit the Tropic of Cancer in the Northern Hemisphere and the Tropic of Capricorn in the Southern Hemisphere perpendicularly.
Due to the tilt of the Earth's axis with respect to the ecliptic plane, the sun's rays hit the Northern Hemisphere directly and the Southern Hemisphere at an oblique angle. This is why when it is summer in one hemisphere, it is winter in the other.
In spring and summer, the sun's rays hit the Equator perpendicularly.
The change from one season to the next is marked by the length of day and night. The first day of summer is the longest day of the year and the first night is the shortest.
Winter begins with the longest night. These days when the difference between the length of night and the length of day is the biggest, are called solstices.
The day and night that mark the beginning of spring and autumn are the same length. They are called equinoxes.
Because the Earth is a sphere, not all the areas of the planet receive sunlight at the same time. As a result, the time of the day varies between some continents and even between countries of the same continent or between cities in the same country.
To unify time, in the 19th century, the Earth was divided into 24 meridians. These are imaginary lines that go from pole to pole, in semicircles. Each area between two meridians was called a time zone.
All the countries and cities that belonged to the same time zone had the same time. Later, the time zones were changed so they were adjusted to borders of countries or regions. This is why the borders of the time zones are so irregular.
Starting from the Greenwich meridian (0º), an hour is added for each time zone going east and an hour is subtracted going west. The calendar day starts at 180º east meridian and ends at 180º west meridian.
The movements of the Earth cause days and nights and also the seasons. We have seen that the number of hours of daylight (day) and darkness (night) vary depending on the season and the hemisphere we are in. In addition to these variations, there are also changes in the average temperature in an area during the year.
Living things can detect these variations. They influence their behaviour and cause them to adapt to their environment.
These are some examples of adaptation:
9sprout: start to grow
Many trees lose their leaves in autumn, when they detect a decrease in the hours of daylight. In the same way they sprout9 new leaves in spring, with the increase in the hours of daylight.
Flowering and forming of fruits also depend on temperatures and hours of daylight and darkness.
Not all plants flower and form fruit in the same season.
Animals are also sensitive to the consequences of the Earth's movements. For example, the mating and breeding seasons of many animals start when the days get shorter and temperatures lower. In this way, the babies will be born during the ideal season for feeding them.
Another example of adaptation is migration. Some birds migrate at certain times of the year.
For example, the majority of the white storks, populations spend the winter in sub-Saharan Africa, and migrate to Europe for the summer.
Activity 19
Can you explain why, if the Earth moves, we don't feel the movement?
Activity 20
Say where the highest temperature would be.
Activity 21
When it's summer in Spain, are we further from the Sun?
Activity 22
Look at the illustration. Is it correct to say that the seasons are caused by the Earth's revolution around the Sun?
Activity 23
Look at the diagram. The Earth rotates from west to east. Explain in your own words why the Sun appears to move across the sky from east to west.
Activity 24
Is there a relation between the length of a day and the existence of leap years?
Activity 25
Complete the text in order to find out if there is any place on the Earth where night or day lasts 24 hours.
Activity 26
If the Sun rises in the East, what time is it in Madrid when it’s 00:00 in Sydney?
Activity 27
Choose whether these sentences are true or false.
Activity 28
Listen and say true or false.
