<em>The Earth's atmosphere interferes with radio waves less than any other wavelength, so the best kind of telescope to build on the Earth's surface would be a radio telescope. Although visible light telescopes are often built on Earth, they are usually put as high up as possible, such as on mountaintops, where there is less atmosphere to get in their way. Radio telescopes are usually put as far down as possible, such as in valleys, to block out human-generated radio signals coming from other parts of the surface of the Earth.
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