Radio waves: If our eyes could see radio waves, we could (in theory) watch TV programs just by staring at the sky! Well not really, but it's a nice idea. Typical size: 30cm–500m. Radio waves cover a huge band of frequencies, and their wavelengths vary from tens of centimeters for high-frequency waves to hundreds of meters (the length of an athletics track) for lower-frequency ones. That's simply because any electromagnetic wave longer than a microwave is called a radio wave.Microwaves: Obviously used for cooking in microwave ovens, but also for transmitting information in radar equipment. Microwaves are like short-wavelength radio waves. Typical size: 15cm (the length of a pencil).Infrared: Just beyond the reddest light we can see, with a slightly shorter frequency, there's a kind of invisible "hot light" called infrared. Although we can't see it, we can feel it warming our skin when it hits our face—it's what we think of as radiated heat. If, like rattlesnakes, we could see infrared radiation, it would be a bit like having night-vision lenses built into our heads. Typical size: 0.01mm (the length of a cell).Visible light: The light we can actually see is just a tiny slice in the middle of the spectrum.Ultraviolet: This is a kind of blue-ish light just beyond the highest-frequency violet light our eyes can detect. The Sun transmits powerful ultraviolet radiation that we can't see: that's why you can get sunburned even when you're swimming in the sea or on cloudy days—and why sunscreen is so important. Typical size: 500 nanometers (the width of a typical bacteria).X rays: A very useful type of high-energy wave widely used in medicine and security. Find out more in our main article on X rays. Typical size: 0.1 nanometers (the width of an atom).Gamma rays: These are the most energetic and dangerous form of electromagnetic waves. Gamma rays are a type of harmful radiation. Typical size: 0.000001 nanometers (the width of an atomic nucleus).
