Recently I saw comparison between an image taken by Spitzer and an image taken by James Webb space telescope (here, for example: https://www.planetary.org/space-images/spitzer-vs-jwst-in-infrared ).

Why there are those rays of light visible around bright starts on the James Webb image (but not on the Spitzer image)? BTW, Is there a specific English term for this effect?

Also, does anybody know what could be the exposition time needed to make these pictures (both, Spitzer and James Webb)?

Diffraction effects from the support structure inside the telescope

https://www.universetoday.com/155062/wondering-about-the-6-rays-coming-out-of-jwsts-test-image-heres-why-they-happen/

https://www.quora.com/What-will-the-diffraction-spikes-on-stars-imaged-by-the-James-Webb-Space-Telescope-look-like#

I see.

So it seems the effect is especially pronounced for 'overexposed' stars. So I guess they can have certain control by using proper exposition time.

But, since we know how the effect is caused, shouldn't we be able to simply remove the effect from the image numerically? If this can be done, I guess they didn't do it just because the image looks more interesting to general population with all those rays sparkling around.

48 minutes ago, Danijel Gorupec said:

I see.

So it seems the effect is especially pronounced for 'overexposed' stars. So I guess they can have certain control by using proper exposition time.

But, since we know how the effect is caused, shouldn't we be able to simply remove the effect from the image numerically? If this can be done, I guess they didn't do it just because the image looks more interesting to general population with all those rays sparkling around.

Do they need to remove the effect?

I imagine the removal of the effects would depend on the goal of the picture. It would be a corruption of data if you were investigating an area of sky near the star, but I imagine you can put an aperture in place if you were looking at the star itself. As noted, those particular stars are overexposed, so you've already screwed up if you were trying to determine their luminosity.

If it's just for PR, it's a neat effect that some people probably like.