The Changing Seasons

Hello Bulb Buddies,

Thank you to all schools who have shared their weather data so far. Remember to contact me if you need any help with this. All schools that enter data to the website will receive prizes at the end of the project, including super scientist pencils and certificates!

As spring approaches, I thought we could look at the changing seasons. There are four seasons in the year. Spring, summer, autumn and winter. In the UK, spring begins in March. When in March depends on which definition you use. The Meteorological definition sees Spring start on 1 March and the Astronomical definition sees it start on 20 March (the Spring Equinox). Spring is when most flowers bloom, the weather gets steadily warmer, and many animals have their young. Lambs in the fields are a good sign that spring has arrived, why not follow the Lamb Cam at St Fagans National Museum of History to see how many lambs are born there!

The summer comes in full force from June to September, and this is when we have the warmest weather and the longest daylight hours. Luckily for you, it’s also when you get your longest school holidays!

Autumn takes hold from late September, and this is when the days become shorter and the weather begins to get colder. This is when the leaves change colour from greens to oranges, reds and browns and fall from the trees. And, when animals like squirrels hoard food for the long winter ahead. Winter arrives again in December, and stays until mid-March.

Do you know why we get seasons? What causes the weather to change so dramatically throughout the year? Well, it’s because the Earth is turning around the Sun at an angle. The picture to the right shows the earth in relation to the sun. The earth turns (rotates) on its axis (imagine a line joining the North and South poles) as it moves around (orbits) the Sun.

It takes the Earth 365 days to travel once around the sun. The length of a planets year is the time it takes for it to complete one orbit of its star. So a year on Earth is measured as the passing of 365 days. 

The picture to the right shows the Earth’s rotation around the Sun. The axis is shown by the white line at the North and South poles. You can see that the axis (white line) is at a different angle to the Earth’s orbit (shown by the white arrows). This means that each day we are at a slightly different angle to the Sun than we were the day before. This is what causes a difference in the number of daylight hours we get. Fewer daylight hours (winter) means less light and heat, making this time of the year colder. More daylight hours (summer) means more light and heat, which makes it warmer!

Many of you have noticed that temperature increases throughout the morning, and decreases in the late afternoon. This is because the heat from the sun gradually warms our surroundings throughout the day. Materials and living things absorb this energy, and become warmer themselves, heating the air around them. The sun is at its highest point around noon, so this is when the earth gets the most light and heat energy from the sun. In the afternoon the heat and light from the sun gradually decreases. However, the materials and living things around you will continue to radiate heat, gradually cooling throughout the afternoon and evening. This is why the temperature is often higher between 2-3pm than it is at midday. This is also why temperatures are lower in winter than they are in summer, because the days are shorter and as such our surroundings receive less heat and light energy from the sun.  

The UK is in what is known as the ‘North hemisphere’, this means we are closer to the North Pole than the South Pole. Notice that in the picture the North pole (the white line pointing up) is leaning towards the Sun in summer and away from the sun in winter. This angle is what causes the change in daylight hours as the Earth orbits the sun over the course of the year.

Other countries experience the changes in daylight hours at different times of the year. In Australia it is summer in December! And in Iceland they have continuous sunlight for days in a row in the summer and darkness for as long in the winter! Imagine having sunlight at midnight!

Keep up the good work Bulb Buddies,

Professor Plant