If these other kinds of telescopes are important, why haven't more people heard about them? First, so-called visible light is the best place to start because humans already have a pair of such "telescopes": their eyes. Galileo built on this fact with his telescope in 1609 and work in "optical" astronomy has progressed from there.
Other wavelengths, however, had more difficult starts. For example, X-rays from space are almost entirely absorbed by the Earth's atmosphere. This meant that X-ray astronomy could not begin until humans figured out how to launch satellites and rockets into space in the middle of the 20th century. But X-ray astronomy has grown up quickly and made incredible progress in just a handful of decades.
Think of Moore's Law - the one that says computing power will double every 18 months. X-ray astronomy has been faster than Moore's law, improving 100 million times in sensitivity in just 36 years.
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