The 300-meter radiotelescope in Arecibo, Puerto Rico (Fig. 25-33), is the world's largest radiotelescope, but many other

Question:

The 300-meter radiotelescope in Arecibo, Puerto Rico (Fig. 25-33), is the world's largest radiotelescope, but many other radiotelescopes are also very large. Why are radiotelescopes so big? Why not make optical telescopes that are equally large? (The largest optical telescopes have diameters of about 10 meters.)