The news about Arecibo got me looking into big telescope installations recently. I’m curious, why are there two super huge radio dishes (Arecibo and FAST), but nothing that size for optical or IR or something?
In: Engineering
1. ~~Building optical telescopes on Earth generally doesn’t get you very good results; the atmosphere distorts the image and isn’t fully transparent (hence why the Hubble is on a satellite)~~ My information was true in the past, but not so much these days. See replies below ↓
2. It’s simply not feasible or practical to build a lens that’s 100m+ across. The largest is 10m (https://www.spaceanswers.com/astronomy/whats-the-largest-optical-telescope-in-the-world/).
3. The reason we have such large dishes is to resolve the much lower frequencies of radio waves – generally, when building a parabolic reflector, the larger the aperture, the lower the frequencies you can resolve. Light is electromagnetic radiation in the order of THz (i.e. trillions of cycles per second), but radio waves are KHz (thousands) or MHz (millions).
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