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The spikes are caused by diffraction of light around the struts supporting the secondary mirror. Hubble has 4 supports for the secondary mirror. JWST has 3 supp
by dr_orpheus 4y ago
The spikes are caused by diffraction of light around the struts supporting the secondary mirror. Hubble has 4 supports for the secondary mirror. JWST has 3 support for the secondary mirror, which because...physics (I don't know I'm not an optics guy)...manifests as 6 diffraction lines.
https://en.wikipedia.org/wiki/Diffraction_spike https://en.wikipedia.org/wiki/Diffraction_spike
EDIT: It may be caused by both the diffraction spikes from the supports struts and the shape of the mirror and aperture. I'm not really sure. The JWST images also seem to have two additional small spikes that look more like the diffraction pattern from a single strut, which could also be a support strut for a stop further down the optics chain.
- WorldMaker 4y agoApparently the Diffraction spikes come from both the primary mirror shapes and the struts holding the secondary mirror. The primary mirrors of the JWST are hexagonal which would explain hexagonal looking effects. The three struts are apparently designed so that two of the struts match the hexagonal mirror angles at all times and are "hidden" inside. (The third strut apparently sometimes causes two much smaller "horizon" spikes for very, very bright objects.) Hank Green on TikTok did a neat, quick demonstration in video form.
- mintyLemon 4y agoLink to that Hank Green video on YouTube: https://m.youtube.com/watch?v=Y7ieVkK-Cz0 https://m.youtube.com/watch?v=Y7ieVkK-Cz0
- loxias 4y agoThe hero we need. Thanks!
- andai 4y agoThese these two pages have some nice visualizations of the optical phenomena: https://blogs.nasa.gov/webb/2022/02/03/photons-incoming-webb-team-begins-aligning-the-telescope/ https://blogs.nasa.gov/webb/2022/02/03/photons-incoming-webb... https://bigthink.com/starts-with-a-bang/james-webb-spikes/ https://bigthink.com/starts-with-a-bang/james-webb-spikes/
- hackernewds 4y agoah an authoritative source. if only we funded scientific exploration more heavily with public funds..
- dr_orpheus 4y agoOh, thank you that makes sense. And due to the folding of the mirror and launch envelope constraints they can't equally space the three struts such that ALL are inside the diffraction of the hexagonal mirror.
- timcederman 4y agoFull explanation: https://stsci-opo.org/STScI-01G6933BG2JKATWE1MGT1TCPJ9.png https://stsci-opo.org/STScI-01G6933BG2JKATWE1MGT1TCPJ9.png