Unit 4 · Earth, Sky and Weather

Step outside. What do you feel? Maybe the sun is warm on your face. Maybe cold wind pushes your hair. Maybe rain drips on your nose. All of that is weather. Weather is what the air is like today.

Weather can change fast. It can be sunny at lunch. It can be rainy at bedtime. That is why we look every day. Looking is the first job of a scientist.

On a sunny day, the sky is clear. You can see the sun. On a cloudy day, clouds cover the sky. The sky looks gray or white.

On a rainy day, water falls from the clouds. On a snowy day, the water falls as soft white flakes. That happens when the air is very cold.

On a windy day, the air moves fast. You cannot see wind. But you see what it does. Flags flap. Leaves fly. Hats blow off.

Is it hot today? Is it cold? Your skin can tell you a little. A thermometer can tell you a number. The number is the temperature. It tells how warm the air is.

Many thermometers have a red line. When the air gets warmer, the line goes up. When the air gets colder, the line goes down. We read the number next to the line.

In Chicago, a winter day may be about 30 degrees. A summer day may be about 85 degrees. A bigger number means warmer air.

One day of weather is easy to remember. Thirty days is hard. So we make a chart. Each day gets a picture. A sun. A cloud. A raindrop. A snowflake.

At the end of the month, we count. How many suns? How many clouds? Counting turns looking into numbers. Numbers help us compare.

Then we look for a pattern. Maybe January had many snow days. Maybe May had many rain days. A pattern is something that happens again and again.

Illinois has four seasons. Winter is cold. Snow may fall. Spring is cool and wet. Plants start to grow. Summer is hot. Fall is cool again. Leaves turn red and gold.

The seasons come in the same order every year. Winter, spring, summer, fall. Then winter again. That is a pattern too. A very big one.

Not every place has the same seasons. But in Illinois, we get all four. Each one brings its own kind of weather.

In summer, the sun comes up early. It stays out late. You can play outside after dinner. In winter, the sun comes up late. It sets before dinner.

The amount of daylight changes with the seasons. Chicago gets about 15 hours of daylight in June. It gets about 9 hours in December. That is a big difference.

More daylight means more sun time. The sun warms the ground longer. That is one reason summer is hot. It is one reason winter is cold.

Most weather is safe. Some weather is not. A tornado is a spinning wind that can knock down houses. A big snowstorm can block roads. A thunderstorm can bring lightning.

Weather scientists watch the sky and make a forecast. A forecast says what the weather will probably be. If a storm is coming, people can get ready.

At school, we practice a tornado drill. We go to a safe hall. We crouch down and cover our heads. On a big snow day, school may close. Forecasts help grown-ups decide.

Before you go out, check the weather. Cold and snowy? Wear a coat, hat, mittens and boots. Rainy? Bring a raincoat and an umbrella. Hot and sunny? Wear light clothes and a hat.

Clothes are like tools. A coat traps warm air near your body. A raincoat keeps water out. A hat keeps sun off your face.

The chart can help you pick. If it has snowed all week, you will probably need boots again. Looking at patterns helps you plan.

Every morning the sun comes up. That is sunrise. It rises on one side of the sky, the east. All day it moves up and across. In the evening it goes down on the other side, the west. That is sunset.

This happens every single day. Sunrise, sky, sunset. Sunrise, sky, sunset. It is one of the strongest patterns there is. People have used it to tell time for a very long time.

The sun looks like it moves. Really, Earth is spinning. That is a big idea for later. For now, watch the pattern.

Put your hand on a sidewalk on a sunny day. It is warm. Now touch a sidewalk in the shade. It is cooler. Sunlight warms what it touches.

The sun warms the ground. It warms the water in a pool or a lake. It warms the air. Without the sun, Earth would be dark and very, very cold.

Too much sun can hurt. It can burn your skin. So wear a hat. Use sunscreen. The sun is a friend, but a powerful one.

A place the sunlight cannot reach is shade. A tree makes shade. A roof makes shade. Your own body makes shade. Look at your shadow.

Sunlight warms what it touches. Shade blocks the light. So things in shade stay cooler. That is why dogs nap under porches. It is why people put up umbrellas at the beach.

You can design shade. Build a tent from a sheet. Put a box over a cup of water. Then feel the difference. Try it and see.

Many people think the moon comes out only at night. Look again. Some days you can see the moon in the blue sky. It looks pale and soft.

The moon does not make its own light. Sunlight bounces off it. That is why we can see it. At night it looks bright against the dark sky.

The moon is far away. It is a big round ball of rock. Astronauts have walked on it. The first ones landed in 1969.

Some nights the moon is a thin curve. Some nights it is half. Some nights it is a full circle. We call these shapes phases. The moon itself does not change. We see different amounts of its lit side.

The phases go in order. Thin, half, full. Then half, thin, gone. Then the pattern starts again. The whole pattern takes about 29 days. Almost one month.

You can check it yourself. Draw the moon every night for a month. Your drawings will show the pattern. Just like Nia did.

When the sun goes down, the sky gets dark. Then the stars come out. Tiny points of light. Some bright, some faint. On a clear night far from city lights, you can see thousands.

The stars are there in the day too. But the sun is so bright it hides them. The sun is a star. It just looks big because it is close.

In Chicago, city lights hide many stars. Drive out to the country and look up. The sky is full.

A telescope is a tube with special glass inside. It makes far things look bigger and closer. Point it at the moon. You will see bumps, lines, and round holes.

The round holes are craters. Space rocks crashed into the moon long ago. Each crash left a hole. Some craters are bigger than Chicago.

About 400 years ago, a scientist named Galileo pointed a telescope at the moon. He saw mountains and holes. Before that, many people thought the moon was smooth. Looking changed the idea.

Earth has two big kinds of places. Land and water. Land can be flat like a field. It can go up like a hill. Illinois is mostly flat, with some hills.

Water comes in many shapes. A river is water that flows along in a line. A lake is water with land all around it. An ocean is water so big you cannot see across it.

Chicago sits next to Lake Michigan. It is one of the biggest lakes in the world. You can stand on the beach and see no other side. But it is still a lake, not an ocean.

A map is a drawing of a place from above. Like a bird would see it. On most maps, blue means water. Green or brown means land.

Find Illinois on a map of the United States. Look at the top right corner of the state. That blue is Lake Michigan. The wiggly line down the left side is the Mississippi River.

You can make a map too. Draw your playground from above. Show the hill. Show where the puddles form. Maps help people find their way and plan.

Look at a globe. Most of it is blue. The ocean covers most of Earth. Ocean water is salty. You cannot drink it. It would make you sick.

Only a small bit of Earth’s water is fresh. Fresh water is not salty. Rivers, most lakes, rain and snow are fresh. That is the water we drink. Lake Michigan is fresh.

Out of every 100 cups of water on Earth, about 97 are salty ocean. Only about 3 are fresh. And most of those 3 are frozen in ice. So fresh water is precious. Do not waste it.

Water can be a liquid. It pours. It splashes. It fills a cup. When it gets very cold, water freezes. It turns to ice. Ice is hard. It keeps its shape.

In winter, ponds in Illinois freeze on top. Puddles turn to ice. Snow is tiny bits of ice. When spring comes, the ice melts back to water.

Freezing and melting go back and forth. Ice, water, ice, water. It is the same stuff. Only the cold changes it.

Water can move the land. In our story, a little river cut a ditch in the sand pile. Real rivers do the same thing. They carry away dirt. That is erosion. Bit by bit, they carve their path.

Some changes are slow. A river bends a little more each year. It takes a lifetime to see. Some changes are fast. A flood can wash away a road in one day.

Wind moves land too. It blows sand into hills called dunes. The Indiana Dunes, near Chicago, were built by wind off Lake Michigan. That took thousands of years.

Wind and water carry land away. People do not always like that. A house on a hill could slide. A beach could wash away. So people find ways to slow it down.

One way is a wall. A stone wall along a shore blocks big waves. Another way is plants. Grass and tree roots hold the dirt like fingers. Bare dirt washes away. Grassy dirt stays.

You can test it. Fill two trays with dirt. Put grass in one. Tilt them and pour water. Which tray loses more dirt?