Gregory's ServerPrimary mirrors in reflecting telescopes cause light waves to interact as they direct light to the secondary mirror. Even if a telescope had no struts, it would still create a diffraction pattern. The shape of the mirror, and any edges it has, determine its pattern. In general, you will get one spike per edge of your mirror. So, JWST's 6-sided mirror makes a 6-pointed pattern. (4/7)
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 JWST’s eight-pointed diffraction spikes are made by two overlapping, 6-pointed patterns, a stronger one from the mirror and a fainter one from the struts. (6/7) |
The number and position of struts holding up the secondary mirror determine the struts’ diffraction spike pattern. When light hits a strut, the light bends into a single, perpendicular pattern shown here by yellow/red/blue dashed lines. Hubble's four struts make a cross-shaped pattern. JWST's three struts make a squished, 6-pointed star pattern. (5/7)