The sun is a star -- a giant ball of hot, glowing gas. It is the closest star to Earth, which is why it looks so big and bright compared to other stars. The sun provides the light and heat that make life on Earth possible. It warms the land and water, drives the weather, helps plants grow, and creates the cycle of day and night. Without the sun, Earth would be a frozen, dark, lifeless planet.
Discuss what the sun does for us: light, heat, energy for plants. Compare the sun to other stars -- it looks big because it is close, not because it is the biggest star. NEVER look directly at the sun -- use shadow activities instead (shadow tracing, sundials). Measure shadows at different times of day to show how the sun's apparent position changes as Earth rotates.
The sun is the most important thing in our sky. It gives us light to see by during the day. It gives us warmth that keeps our planet at a temperature where water can be liquid and life can thrive. Without the sun, Earth would be a dark, frozen ball of rock drifting through space.
But what IS the sun? The sun is a star -- the very same kind of object as the tiny twinkling points of light you see in the night sky. It does not look like those distant stars because it is enormously closer to us. The sun is about 150 million kilometers from Earth. That sounds far, but the next closest star, Proxima Centauri, is about 40 trillion kilometers away -- more than 250,000 times farther. That is why the sun looks like a big, bright disk while other stars look like tiny dots.
The sun is a huge ball of extremely hot, glowing gas -- mostly hydrogen and helium. It is NOT on fire like a campfire or a match. Instead, the sun produces energy through a process called nuclear fusion. Deep in the sun's core, where the temperature is about 15 million degrees Celsius, hydrogen atoms are squeezed together so tightly that they fuse (combine) to form helium, releasing tremendous amounts of energy. This energy works its way to the surface and radiates out into space as light and heat.
That light and heat are what make Earth livable. Sunlight warms the land and ocean, creating the temperature differences that drive weather. Plants capture sunlight and use it to make food -- and nearly every animal on Earth, including humans, depends on plants for food. The sun heats ocean water, causing evaporation that starts the water cycle and brings rain to the land. The sun's energy is behind almost everything that happens on Earth's surface. It is, quite literally, the source of life.