The Earth is not static, it moves through the space following two movements: rotation and revolution.



ROTATION

Like a spinning top, the Earth is always rotating around its axis. The axis is an imaginary line that crosses through the center of the Earth connecting the North and the South Poles.

The Earth completes one rotation every 24 hours (1 day). The rotation of the Earth causes day and night.

The Earth rotates anticlockwise: the Sun rises in the East and it sets in the West.


Tilted Axis.jpg
THE EARTH'S AXIS IS AN IMAGINARY LINE

Globespin.gif
Source: www.en.wikipedia.org



REVOLUTION

But the Earth not only rotates on its axis it also revolves around the Sun.

A complete orbit around the Sun occurs every 365 days (1 year).

Earth's Revolution.jpg
THE EARTH REVOLVES AROUND THE SUN



THE SEASONS

The seasons are caused because the Earth's rotation axis is not straight, it is tilted (23.5 degrees). That means that part of the Earth leans towards the Sun, and another part of the Earth leans away from the Sun.

That is why different parts of the Earth receive different amounts of sunlight and heat: the part that leans towards the Sun will receive more sunlight and heat; while the part that leans away from the Sun will recive less sunlight and heat.


Lean towards.jpg
THE NORTHERN HEMISPHERE LEANS TOWARDS THE SUN (SO IT GETS MORE LIGHT AND HEAT), AND THE SOUTHERN HEMISPHERE LEANS AWAY FROM THE SUN (SO IT GETS LESS LIGHT AND HEAT).


Lean away.jpg
THE NORTHERN HEMISPHERE LEANS AWAY FROM THE SUN (SO IT GETS LESS LIGHT AND HEAT) AND THE SOUTHERN HEMISPHERE LEANS TOWARDS THE SUN (SO IT GETS MORE LIGHT AND HEAT).


So, when the Northern hemisphere leans towards the Sun, the Southern hemisphere will lean away from the Sun: in the Northern hemisphere it will be summer (it will receive more sunlight and heat), and in the Sourthern hemisphere it will be winter (it will receive less sunlight and heat).

And when the the Southern hemisphere leans towards the Sun, the Northern hemisphere will lean away from the Sun: in the Southern hemisphere it will be summer, and in the Northern hemisphere it will be winter.



Autumn and spring are transit seasons: the Earth's axis doesn't tilt towards or away from the Sun. In autumn and spring the Earth's axis is tilted to one side, that is why most parts of the Earth receive the same amount of sunlight and heat.

Let's see a picture to ease this explanation: the seasons in the Northern hemisphere (click on the picture to make it bigger).


Seasons.jpg
Source: www.en.wikipedia.org

Time for the videos.

On the first video you could check what causes day and night.




On the second video, you could watch how the Earth revolves around the Sun.




On the third video you could watch how the seasons change.




Do you like to check what you have learned? Go to the games section.