Electromagnetic radiation and telscopes

What do radio waves, infrared radiation, visible light, ultraviolet radiation, X-Rays and gamma rays have in common? How do they differ? Do astronomers look at visible light only? If not, how can they "see" objects in space at other frequencies? First of all, all these are electromagnetic waves. All these waves are invisible to human eye except visible light. Since all of these are waves, they all vibrate. But the number of times they vibrate per second is different. These waves do not have same wavelength and frequency. This is why none of them have same velocity. Some of these waves like ultra violet and gamma are very dangerous to living cells. Other waves like radio and visible light are harmless and we are exposed to them almost all the time. The astronomers do not look only for visible lights. If they had looked only for visible lights our science books would have been very thin.  They look for all sorts of waves regardless of their frequency.  They use optical telescopes for this.