## Section 5.3: How do we see the invisible?

It can be difficult to comprehend how Astronomers use 'invisible' electromagnetic radiation like radio waves and X-rays to observe the universe. The detectors that measure the radiation don’t ‘take pictures’ in the way that conventional optical telescopes do.  Instead, the electrical signals they receive need to be converted into something we can readily perceive. Some imaginative ways of doing this are described next.