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> I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? Some of the remaining misalignm

> I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? Some of the remaining misalignment is rather obvious in the higher resolution image. For example, look left of the main star and notice an "echo" of the main diffraction pattern that is not centered on a star. Also, if you follow that pattern's downward arm to where it meets a diagonal arm of the main pattern you see a rectangular bar of increased brightness. Perhaps it indicates the need for calibrating that part of the sensor. https://www.nasa.gov/sites/default/files/thumbnails/image/telescope_alignment_evaluation_image_labeled.png https://www.nasa.gov/sites/default/files/thumbnails/image/te...

sbierwagen 5y ago
There's five echos, actually. (Look north, northwest, W, SW and S) Internal reflections, probably. HD 84406 is fairly bright, magnitude 6, eye-visible. In one of the blog posts they say it's too bright to be imaged in normal operations: https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-back-on-successful-deployments/ https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-b... (You don't spend tens of billions to put a telescope into orbit just to look at HD catalog stars) All the other sensor cruft would go away with dark-frame subtraction: https://en.wikipedia.org/wiki/Dark-frame_subtraction https://en.wikipedia.org/wiki/Dark-frame_subtraction They're apparently not bothering with that for mirror alignment photos. Another safe bet is that a bunch of the sensor noise is because all the instruments are still warm. NIRCAM is still at 42K, and MIRI is hotter. https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.htm... It doesn't look like they've turned on the instrument coolers yet.

sbierwagen 5y ago

There's five echos, actually. (Look north, northwest, W, SW and S) Internal reflections, probably. HD 84406 is fairly bright, magnitude 6, eye-visible. In one of the blog posts they say it's too bright to be imaged in normal operations: https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-back-on-successful-deployments/ https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-b... (You don't spend tens of billions to put a telescope into orbit just to look at HD catalog stars) All the other sensor cruft would go away with dark-frame subtraction: https://en.wikipedia.org/wiki/Dark-frame_subtraction https://en.wikipedia.org/wiki/Dark-frame_subtraction They're apparently not bothering with that for mirror alignment photos. Another safe bet is that a bunch of the sensor noise is because all the instruments are still warm. NIRCAM is still at 42K, and MIRI is hotter. https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.htm... It doesn't look like they've turned on the instrument coolers yet.