[rbliss]

Yes, it's a combination of both the primary mirror and struts. The JWST website has a very helpful infographic explaining: https://webbtelescope.org/contents/media/images/01G529MX46J7...

[creatonez]

Here is an image showing how each part of the distortion comes about - https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB...

[moffkalast]

That's quite exhaustive, but it makes me wonder why isn't anything done to correct for that. Like for example instead of taking one 15h exposure, why not take three 5h exposures and roll the telescope 5 degrees in between, then median filter out the artefacts?

[sbierwagen]

JWST does have a roll dither mode: https://jwst-docs.stsci.edu/jwst-general-support/jwst-dither... Don't know why they didn't use it. Maybe they were trying to observe as many targets as possible for the initial release of imagery.

[creatonez]

Mainly because it doesn't matter. They're not looking at the stars in the foreground, they're looking at the background which is much further away. The diffraction pattern is actually super dim -- those foreground stars are just very bright due to the exposure.

[AnonMO]

It took like 5 months to cool web to operational temperatures rolling the telescope would create so much heat all new images would be useless until it cools down again.

[MontagFTB]

You beat me to it- incredibly helpful diagram. Thanks for sharing it.

[coldpie]

Wow, thanks for this link. The level of communication around JWST's technology and launch has been amazing, and this is a great example of that.