Glossary · Vật lý
Electromagnetic radiation
Energy travelling through space as electromagnetic waves, spanning from very long radio waves to very short gamma rays. Visible light is only a narrow band within it.
Electromagnetic radiation is ONE phenomenon spread across a continuous spectrum, not several different ones. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays differ only in wavelength and frequency.
The higher the frequency, the more energy each photon carries. Above a certain threshold that energy is enough to knock electrons out of atoms; such radiation is called ionising. Gamma rays, X-rays and some ultraviolet fall in this group, and they can damage living cells — harmfully, as in sunburn, or by design, as in cancer radiotherapy.
Earth's atmosphere is transparent only to some bands: visible light and most radio waves pass through, while cosmic X-rays and gamma rays are almost entirely blocked. That is why X-ray telescopes have to be placed in orbit.