Weather and the Sky

Look Up at the Sky

Every single day, something is happening above your head. Maybe the Sun is blazing in a clear blue sky. Maybe grey clouds are gathering and a cool wind is picking up. Maybe rain is drumming on the roof, or snowflakes are drifting down. All of this is weather, and it is one of the most exciting shows in nature — and it is free to watch any time you like.

Weather is simply what the air and the sky are doing right now. It changes from hour to hour and from place to place. In this book, we will discover where clouds come from, why it rains, how the wind blows, what makes a thunderstorm rumble, and how you can learn to read the sky like a weather expert.

The Air All Around Us

Weather all happens inside a giant blanket of air that wraps around the whole Earth. This blanket is called the atmosphere. You cannot see air, but you can feel it when the wind blows and you can watch it push the clouds along.

Two things power almost all of our weather. The first is the Sun, which warms the air, the land and the sea. The second is water, which is always rising into the sky and falling back down again. When you understand how the Sun and water work together, you understand the secret behind clouds, rain, wind and storms.

Where Clouds Come From

Clouds might look like soft, solid pillows, but they are really made of millions of tiny water droplets and ice crystals, so small and light that they float in the air.

Here is how a cloud is born. The Sun warms water on the ground, in puddles, lakes and oceans. Some of that water turns into an invisible gas called water vapour and rises up into the sky. This is called evaporation.

High up, the air is much colder. When the rising vapour cools down, it turns back into tiny droplets of water. This is called condensation. Billions of these droplets gather together, and that is a cloud! So every cloud you see in the sky started life as water on the ground.

Different clouds tell different stories. Big, fluffy white clouds on a sunny day usually mean fine weather. Thin, wispy clouds high up can be a sign that the weather is about to change. And dark, heavy grey clouds piling up tall often mean that rain or a storm is on the way.

Why It Rains

A cloud cannot hold its water forever. As more and more droplets gather, they bump into each other and join together to make bigger and bigger drops. When a drop grows too heavy to float, it falls out of the cloud — and that falling water is rain.

If the air is cold enough, the water freezes on the way down and falls as snow, in delicate six-sided crystals, or as little balls of ice called hail. Rain, snow and hail are all forms of water falling from the sky, and scientists give them one big name: precipitation.

After the rain reaches the ground, it flows into streams and rivers, runs back to the sea, and then the Sun lifts it up again to make new clouds. This never-ending journey is called the water cycle, and it keeps the same water moving around our planet over and over.

The Wind

Have you ever wondered what makes the wind blow? Wind is simply air that is moving — and the Sun is what gets it going.

The Sun does not warm the Earth evenly. It heats some places more than others. Warm air is light and rises upward. Cooler air is heavier and rushes in to take its place. That rushing, moving air is what we feel as wind.

Wind can be a gentle breeze that barely stirs the leaves, or it can be a powerful gale strong enough to bend trees and toss waves on the sea. Wind helps shape our weather by pushing clouds from place to place and carrying warm or cold air across the land. People have used the wind for thousands of years — to sail ships, to turn windmills, and today to spin wind turbines that make electricity.

Storms, Thunder and Lightning

Sometimes the weather puts on its most dramatic show of all: a thunderstorm. Storms happen when warm, wet air rushes upward very fast and builds enormous, towering clouds.

Inside these giant clouds, tiny bits of ice and water rub and bump together, building up a powerful electric charge — a bit like the crackle you sometimes feel from a woolly jumper. When the charge grows strong enough, it leaps out as a brilliant flash of lightning, one of the most powerful bursts of electricity in nature.

Lightning heats the air around it so suddenly and so fiercely that the air bangs outward, making the loud rumble we call thunder. Lightning and thunder happen at exactly the same moment, but we see the flash first because light travels faster than sound. The closer the storm, the smaller the gap between the flash and the bang.

Reading the Sky and the Seasons

For thousands of years, before there were weather apps and satellites, people learned to read the sky to guess what was coming. A red sky in the evening often promised fine weather the next day. Animals puffing up their feathers or fur sometimes hinted that a cold spell was near. You can become a sky-reader too, just by watching the clouds, feeling the wind, and noticing how the air changes before rain arrives.

Over a whole year, the weather follows a bigger pattern called the seasons — spring, summer, autumn and winter. The seasons happen because the Earth is tilted as it travels around the Sun. For part of the year your half of the world leans toward the Sun, bringing long, warm summer days. Later it leans away, bringing short, cold winter days. The seasons turn like a great slow wheel, year after year.

What We Learned

Weather is what the air and sky are doing right now, and it is powered mainly by the Sun and by water. The Sun lifts water into the sky, where it cools to make clouds, then falls again as rain or snow. Wind is moving air, set going because the Sun warms the Earth unevenly. Storms, lightning, rainbows and seasons all come from these same simple ideas working together. Next time you step outside, look up — there is always a wonderful story unfolding in the sky.

To follow water on its endless journey through the sky, read The Amazing World of Water. Or discover the crackling electricity that powers lightning in The Story of Electricity.