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Is the JWST Limited to Just Infrared Measurements?

-- Neil Pollick | January 25, 2022

Question:

I understand that infrared and visible-light telescopes have the same basic construction, namely a lens or mirror to focus the radiation on to some sort of collecter/sensor. So what makes the James Webb telescope a specifically infra red telescope? Could it be retasked to make images of the objects or phenomena that give out radiation in the visible part of the spectrum? Or is there something in its construction that limits it to infrared radiation?

-- Neil Pollick

Answer:

In fact, JWST does observe at the longest wavelengths included in the visible part of the electromagnetic spectrum. The JWST instrument description includes a wavelength range diagram which shows that it can observe down to about 0.6 micron wavelength. Our eyes would perceive this wavelength of light as orange/red. I believe that the JWST mirror could be used for shorter wavelength (i.e. wavelengths more in the optical part of the electromagnetic spectrum) observations, but these measurements would be much less efficient as the mirror is tuned for longer-wavelength measurements. Also, the detectors on-board JWST are specifically designed to operate at infrared wavelengths.

-- Jeff Mangum

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