4 ms·

A lot of the pictures have some bright stars with 6 long lens flare like points coming out of them in a consistent pattern. Is that because of the hexagonal sha

A lot of the pictures have some bright stars with 6 long lens flare like points coming out of them in a consistent pattern. Is that because of the hexagonal shape of JWT's lenses/mirrors?

deelowe 4y ago
More or less. That's how they've explained it in the past.
mackieem 4y ago
Yeah, it's the hexagonal shape. The objects with the 6 diffraction spikes are overexposed compared to the rest of the objects in the picture, so they're generally brighter and/or closer objects. https://www.youtube.com/watch?v=UBcc3vpJTAU https://www.youtube.com/watch?v=UBcc3vpJTAU
ceejayoz 4y ago
It's not the mirrors, it's the three struts supporting the reflector. Hubble shows four spikes because it has two struts. https://bigthink.com/starts-with-a-bang/james-webb-spikes/ https://bigthink.com/starts-with-a-bang/james-webb-spikes/ https://www.universetoday.com/155062/wondering-about-the-6-rays-coming-out-of-jwsts-test-image-heres-why-they-happen/ https://www.universetoday.com/155062/wondering-about-the-6-r...
- krajzeg 4y ago
  I think you also had a similar comment and linked the same article under the previous topic about JWST's first image? The article is very informative, but my read of it is different: the three major "spikes" are in fact due to the hexagonal shape of the mirrors and how they're laid out. The struts also add three spikes, but: two of them coincide with the mirror spikes, while one of them (from the vertical strut) is visible on its own, and causes the smaller perfectly horizontal spike. The image I'm basing this on is in your article with a caption starting from "The point spread function for the James Webb Space Telescope" [1] [1]: https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB-Ho.png?resize=1024,461 https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB...
rbliss 4y ago
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/01G529MX46J7AFK61GAMSHKSSN?page=2&filterUUID=91dfa083-c258-4f9f-bef1-8f40c26f4c97 https://webbtelescope.org/contents/media/images/01G529MX46J7...
- MontagFTB 4y ago
  You beat me to it- incredibly helpful diagram. Thanks for sharing it.
- coldpie 4y ago
  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.
- moffkalast 4y ago
  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?
  - AnonMO 4y ago
    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.
    - moffkalast 4y ago
      That makes no sense, they have to rotate it every time they take a picture otherwise they'd be looking at the same spot all the time. Motors don't emit that much heat and neither do torque wheels. Though I suppose now that I think of it, it's possible the main mirror assembly actually has no built in roll control but only pitch, since the yaw part could be done by moving the entire telescope while remaining shaded. I've never seen any videos showing the full movement, but the previews for LUVIOR show it having full 3 degree articulation relative to the heatsink segment, so I assumed the Webb also has it given that they're extremely similar designs. https://www.youtube.com/watch?v=uzFEaCYhmEs https://www.youtube.com/watch?v=uzFEaCYhmEs
MontagFTB 4y ago
Here’s an infographic from NASA explaining the phenomenon: https://webbtelescope.org/contents/media/images/01G529MX46J7AFK61GAMSHKSSN https://webbtelescope.org/contents/media/images/01G529MX46J7...
deanCommie 4y ago
From the other comments, I understand why it's there, but i wish they would photoshop them out. The images take on a more synthetic and fake quality when the technical physical man-made constraints of our telescope get projected out onto the natural very much NON-man-made universe. Look at https://stsci-opo.org/STScI-01G7ETPF7DVBJAC42JR5N6EQRH.png https://stsci-opo.org/STScI-01G7ETPF7DVBJAC42JR5N6EQRH.png and observe the incredible entropy in the nebula itself. The consistent, perfect, straight lines, of each star are jarring in the image.
- deanCommie 4y ago
  to be clear - i realize these are for science. they shouldn't be edited for scientists. but we should edit them :)
micromacrofoot 4y ago
Also, I recall reading that those stars are so bright because they're within our galaxy... so they're the foreground really

A lot of the pictures have some bright stars with 6 long lens flare like points coming out of them in a consistent pattern. Is that because of the hexagonal shape of JWT's lenses/mirrors?

deelowe 4y ago

More or less. That's how they've explained it in the past.

mackieem 4y ago

Yeah, it's the hexagonal shape. The objects with the 6 diffraction spikes are overexposed compared to the rest of the objects in the picture, so they're generally brighter and/or closer objects. https://www.youtube.com/watch?v=UBcc3vpJTAU https://www.youtube.com/watch?v=UBcc3vpJTAU

ceejayoz 4y ago

It's not the mirrors, it's the three struts supporting the reflector. Hubble shows four spikes because it has two struts. https://bigthink.com/starts-with-a-bang/james-webb-spikes/ https://bigthink.com/starts-with-a-bang/james-webb-spikes/ https://www.universetoday.com/155062/wondering-about-the-6-rays-coming-out-of-jwsts-test-image-heres-why-they-happen/ https://www.universetoday.com/155062/wondering-about-the-6-r...

krajzeg 4y ago
I think you also had a similar comment and linked the same article under the previous topic about JWST's first image? The article is very informative, but my read of it is different: the three major "spikes" are in fact due to the hexagonal shape of the mirrors and how they're laid out. The struts also add three spikes, but: two of them coincide with the mirror spikes, while one of them (from the vertical strut) is visible on its own, and causes the smaller perfectly horizontal spike. The image I'm basing this on is in your article with a caption starting from "The point spread function for the James Webb Space Telescope" [1] [1]: https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB-Ho.png?resize=1024,461 https://bigthink.com/wp-content/uploads/2022/03/FOFC8ZPX0AIB...

rbliss 4y ago

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/01G529MX46J7AFK61GAMSHKSSN?page=2&filterUUID=91dfa083-c258-4f9f-bef1-8f40c26f4c97 https://webbtelescope.org/contents/media/images/01G529MX46J7...

MontagFTB 4y ago
You beat me to it- incredibly helpful diagram. Thanks for sharing it.
coldpie 4y ago
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.
moffkalast 4y ago
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?
- AnonMO 4y ago
  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.
  - moffkalast 4y ago
    That makes no sense, they have to rotate it every time they take a picture otherwise they'd be looking at the same spot all the time. Motors don't emit that much heat and neither do torque wheels. Though I suppose now that I think of it, it's possible the main mirror assembly actually has no built in roll control but only pitch, since the yaw part could be done by moving the entire telescope while remaining shaded. I've never seen any videos showing the full movement, but the previews for LUVIOR show it having full 3 degree articulation relative to the heatsink segment, so I assumed the Webb also has it given that they're extremely similar designs. https://www.youtube.com/watch?v=uzFEaCYhmEs https://www.youtube.com/watch?v=uzFEaCYhmEs

MontagFTB 4y ago

Here’s an infographic from NASA explaining the phenomenon: https://webbtelescope.org/contents/media/images/01G529MX46J7AFK61GAMSHKSSN https://webbtelescope.org/contents/media/images/01G529MX46J7...

deanCommie 4y ago

From the other comments, I understand why it's there, but i wish they would photoshop them out. The images take on a more synthetic and fake quality when the technical physical man-made constraints of our telescope get projected out onto the natural very much NON-man-made universe. Look at https://stsci-opo.org/STScI-01G7ETPF7DVBJAC42JR5N6EQRH.png https://stsci-opo.org/STScI-01G7ETPF7DVBJAC42JR5N6EQRH.png and observe the incredible entropy in the nebula itself. The consistent, perfect, straight lines, of each star are jarring in the image.

deanCommie 4y ago
to be clear - i realize these are for science. they shouldn't be edited for scientists. but we should edit them :)

micromacrofoot 4y ago

Also, I recall reading that those stars are so bright because they're within our galaxy... so they're the foreground really