Radiant energy is energy that travels in waves through space, like light from the sun or heat from a fire. Unlike energy that needs to travel through something solid (like sound waves traveling through air), radiant energy can move through empty space. That's why sunlight reaches Earth even though there's a vacuum between the sun and our planet.

The most familiar form of radiant energy is visible light, the energy that lets you see this page. But radiant energy includes many types of waves your eyes can't detect: infrared waves that you feel as heat, the microwaves that warm your food, the radio waves that carry music to your car, and the X-rays dentists use to check your teeth. All these different forms of radiant energy travel at the same incredible speed: the speed of light, about 186,000 miles per second.

Scientists call it radiant because it radiates outward from its source in all directions, like ripples spreading across a pond. When you turn on a lamp, radiant energy spreads throughout the room. When the sun rises, its radiant energy spreads across half the Earth at once, warming the ground, helping plants grow, and powering solar panels that convert that energy into electricity.