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
In order to make a good reflector you need to make sure that any flaws/imperfections in your reflector are smaller than the wavelength of the radiation you’re trying to reflect, otherwise the flaws in your reflector will screw up your image.
Radio waves have wavelengths that are measured in meters. Building something to that degree of precision is fairly easy to achieve on a REALLY large scale.
Visible light has a wavelength measured in nanometers, which ends up limiting the practical size of visible light optics to maybe a few meters.
There is also a secondary concern – how much does the atmosphere mess up your observations? You mention IR in your post. A lot of the IR wavelengths are absorbed by earths atmosphere, and may of the ones that are not tend to be wavelengths that are emitted by the earths atmosphere.
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