This question asks whether any ground-based telescopes can see the James Webb. The answer ("yes, but it's basically just an indistinct dot") is deeply underwhelming. If only we had a much better telescope that we could use to look at it...

What would the James Webb see if it imaged itself from Earth Orbit?

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The answer is going to be deeply underwhelming regardless of what telescope you use, because of the sunshield, and because of its location.

It lives at the Earth-Sun L2 point, as shown on this handy diagram from wikipedia:

Diagram of the Earth-Sun lagrange points

this means we will always be on the sunward-side of the device, which means all we will ever be able to see is the sun-side of the sun-shield. Wikipedia has this image:

Rendering of the underside of the JWST

That's a visible-light rendering, of course, and I'm not entirely sure what it would look like in the IR spectra that the JWST sees in. NIRCam can see 600nm light (orangey). I can't see what angular resolution it has for visible-light imaging, but for near IR at 2000nm it is 0.07 seconds of arc. The face of the sunshield will be at a nice warm 383K so it'll be visible to at least one of the JWST's sensors, I'm sure.

The L2 point is ~1.5 million km away from Earth, and at that distance 0.07 arc seconds is equivalent to a feature size of a little over 500m. Given that the JWST is 20m long in its largest dimension, you're not actually going to get a blurry image... you're going to get a single pixel. Technically, it might be quite sharp. Just not very interesting.


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