Email or username:

Password:

Forgot your password?
Kelly's posts Post Back to profile
Top-level
Kelly Lepo

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)

Webb's diffraction spikes: Strut Influence. Illustrations of struts, the spike created perpendicular to the strut, spikes at detector focus, and the resulting spike pattern. For two struts: two parallel lines are shown perpendicular to the struts. These combine to a single horizontal line at the detector focus, and the resulting spike pattern is two horizontal spikes, one to the left and one to the right of the central point. For four struts: two sets of parallel lines are shown perpendicular to the struts. One set is horizontal (perpendicular to the vertical struts) and one set is vertical (perpendicular to the horizontal struts). These combine into a cross shape at the detector focus, making a four-pointed spike pattern. For three struts: three lines are shown perpendicular to the struts. One is horizontal, one slopes downward and one slopes upward. This combines into three overlapping lines at the detector focus, creating a squished 6-pointed spike pattern.
8 Nov 2022 at 19:30 | Open on astrodon.social
1 comment
Kelly Lepo

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)

Webb’s Eight-Pointed Stars. A diagram shows how the two diffraction patterns overlap: “Strut Influence" a smaller, squished, 6 pointed star and "primary mirror influence", a larger, evenly spaced, 6-pointed star. Four of the "strut Influence" spikes overlap with the "primary mirror influence" spikes. The the horizontal "strut Influence" spikes do not overlap. The same is true for the vertical "primary mirror influence" spikes. The combination of the two patterns makes an 8-pointed star.
8 Nov 2022 at 19:31 | Open on astrodon.social
Go Up