Radiation is energy that travels through space in the form of invisible waves or tiny particles. The sun radiates light and heat across 93 million miles of empty space to warm Earth. Your cell phone radiates radio waves to communicate with cell towers. When you feel warmth from a campfire without touching it, you're experiencing infrared radiation traveling through the air to your skin.

Not all radiation is the same. Some forms, like visible light and radio waves, are harmless. You're surrounded by these all the time. Other forms, like X-rays and gamma rays, carry much more energy and can be dangerous in large amounts, which is why the dentist covers you with a heavy apron during X-rays. The word radioactive describes materials that naturally give off powerful radiation, like uranium.

Scientists measure radiation in different ways depending on what they're studying. The energy itself, how much is absorbed by something, and the biological effect on living things all matter in different situations. Understanding radiation helps us use it safely and beneficially: doctors use radiation to see inside bodies and treat cancer, while engineers use it to generate electricity in nuclear power plants.