If you were lost in the middle of the woods and could not see the Sun, you might use a compass to try to decide which direction to take. A magnetic compass needle lines itself up with Earth’s magnetic field and points roughly north and south: from that, you can figure out east and west, too. Because this works fairly well, people have been using magnetic compasses to find their way for about 1,000 years.
If you have ever gone swimming in summer or had a snowball fight in winter, then you know something about seasons. Seasons are times on Earth that have very specific weather patterns and hours of daylight. Earth’s four seasons are spring, summer, fall, and winter. Seasons are caused by Earth’s changing position as it revolves around the Sun. Some people think that the seasons occur because of Earth’s distance from the Sun.
Joseph Henry Image: Library of Congress, Prints & Photographs Division, LC-BH824-4499
Your team has a soccer game Saturday, so you check a local news station’s website to see the weekend forecast. Radar images on multicolored maps show rain moving east, away from your town, and bands of clouds a few hundred miles west. It could mean rain, but the forecast for Saturday is partly cloudy with a high of 75 degrees. To get a better idea of the weather at the time of your game, you check the hour-by- hour forecast. Saturday, 10 a.m.: partly sunny and 68 degrees. Perfect.
In this age of 10-day weather forecasts and colorful digital displays of the entire country’s weather, it is hard to imagine not being able to find out tomorrow’s forecast. But before the mid-1800s, farmers and ship captains, whose lives and jobs depended on the weather, had little information to go on. They relied on clouds, winds, The Old Farmer’s Almanac, past experience in how the seasons flow, animal behavior signs, and their own arthritic bones to make predictions about the weather. But a scientist named Joseph Henry changed all of that.
What is your favorite thing to do in autumn? Go on a hayride? Walk through a pumpkin patch or an apple orchard? Watch leaves dance around you?
Autumn is a beautiful and fun season for all ages. We can observe a lot of changes in autumn—the air becomes crisp, the evenings grow longer, and leaves’ dazzling colors emerge. We know autumn is here when the bright green summer landscape changes to reveal brilliant reds, oranges, yellows, and golds. But leaves are not on trees just to make them pretty. Trees need leaves to keep them alive!
Leaf or Needle?
When the lights in the movie theater dim and cell phones are muted, the movie is about to begin. In the dark, you can hear an occasional cough or the rustle of candy wrappers and smell the aroma of buttered popcorn. The screen begins to reflect light. Welcome to the world according to Hollywood, a world of make-believe made from moving images and digital sound.
When you get hungry, you grab a snack from your fridge or pantry. But what can plants do when they get hungry? You are probably aware that plants need sunlight, water, and a home (like soil) to grow, but where do they get their food? They make it themselves!
Plants are called autotrophs because they can use energy from light to synthesize, or make, their own food source. Many people believe they are “feeding” a plant when they put it in soil, water it, or place it outside in the Sun, but none of these things are considered food. Rather, plants use sunlight, water, and the gases in the air to make glucose, which is a form of sugar that plants need to survive. This process is called photosynthesis and is performed by all plants, algae, and even some microorganisms. To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight.
By taking in water (H2O) through the roots, carbon dioxide (CO2) from the air, and light energy from the Sun, plants can perform photosynthesis to make glucose (sugars) and oxygen (O2). CREDIT: mapichai/Shutterstock.com
A thunderstorm is a disturbance in the atmosphere that is characterized by lightning and thunder. Lightning is an electrical discharge in the air generated by charged particles in moving air masses. Because lightning is a phenomenon of moving, charged particles, not rain, we see lightning in violent forest fires and volcanoes as well as thunderstorms. Thunder is the sound produced by the shock wave lightning generates. The air immediately around lightning is suddenly heated to high temperatures—up to 30,000°C (54,000°F)—and subjected to high pressure; it expands rapidly.
Have you ever heard someone say, “Clouds are just water vapor”? Next time, you’ll be able to correct them.
While it’s true that clouds contain water, they actually aren’t made of water vapor. If they were, you wouldn’t be able to see them. The water that makes up clouds is in liquid or ice form. The air around us is partially made up of invisible water vapor. It’s only when that water vapor cools and condenses into liquid water droplets or solid ice crystals that visible clouds form.