Seasonal Variations Why do we have seasons ? (continued…)

Activity Using the data collected, each student must draw a graph of the Sun’s altitude versus Time.

Look at the recorded results we have for the altitude of the sun over the last few weeks. Is there a trend emerging?

What we should notice is the Sun’s altitude either increases or decreases over time as we take measurements. In the Spring there should be an increase, whereas the Sun’s altitude is decreasing in the Autumn.

Graph showing Sun’s altitude

Analyse the graph What is the significance of the dates of the peak and trough ? Highest point = Summer Solstice Lowest point = Winter Solstice

What does this mean? It can be seen from this simple diagram that different parts of the Earth are more directly exposed to the light from the Sun at different times of the year. For example, in June the northern hemisphere of the Earth is tilted towards the Sun whereas the southern hemisphere is tilted away. This results in Summer in the northern hemisphere and Winter in the southern hemisphere.

The exact opposite is true 6 months later, when the Earth reaches the point in its orbit where the southern hemisphere is tilted towards the Sun and the northern hemisphere is tilted away from the Sun. At this point the southern hemisphere experiences its Summer and the northern hemisphere experiences its Winter.