Why stars look spiky in images from the James Webb Space Telescope

The first full-color image released from the JWST. | Image: NASA, ESA, CSA, STScI

Stars in the new images from the James Webb Space Telescope look sharper than they did before. And I’m not just talking about the image quality, which is astounding. I’m talking about the fact that many of the bright stars in the images have very distinct Christmas-ornament-looking spikes or, as one of my colleagues put it, “It looks like a J.J. Abrams promo poster, and I love it.”

But this isn’t a case of too much lens flare. Those are diffraction spikes, and if you look closely, you’ll see that all bright objects in the JWST images have the same eight-pointed pattern. The brighter the light, the more prominent the feature. Dimmer objects like nebulae or galaxies don’t tend to see quite as much of this distortion.

This pattern of…

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