In Hubble’s case, its four struts resulted in the four distinct spikes you see in Hubble pictures. Light passing by these struts gets diffracted, resulting in more spikes, each one perpendicular to the strut itself. In the case of JWST, the struts are 25 feet long.
Secondary mirrors are smaller than primary mirrors and are held in place some distance away from the primary mirror by struts. But JWST has hexagonal mirrors that result in an image with six diffraction spikes. In Hubble’s case, the mirror was round, so it didn’t add to the spikiness. So the shape of the mirror itself can result in these spikes of light as light interacts with the edges of the mirror. Light diffracts, or bends, around objects like mirror edges. The secondary mirror on space telescopes helps guide that light toward the science instruments that turn it into all the cool images and data we’re seeing now.īoth the primary and secondary mirrors contribute to the diffraction spikes but in slightly different ways. Reflecting telescopes have a large primary mirror that gathers the light and reflects it back to a smaller secondary mirror. Both Hubble and JWST are reflecting telescopes, which means that they collect light from the cosmos using mirrors. The shape of the diffraction spikes is determined by the telescope’s hardware, so let’s start with a quick refresher of the important bits. Hubble stars have four spikes in a cross.
(Two of JWST’s spikes can be very faint, so it sometimes appears as though there are six.)įrom this moment on you will always be able to tell the difference between a Hubble image and a JWST image: If you compare images taken by the new telescope to images taken by its predecessor, you’ll notice that Hubble only has four diffraction spikes to JWST’s eight. This pattern of diffraction spikes is unique to JWST. Dimmer objects like nebulae or galaxies don’t tend to see quite as much of this distortion. The brighter the light, the more prominent the feature. 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. Abrams promo poster, and I love it.”īut this isn’t a case of too much lens flare. 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. And I’m not just talking about the image quality, which is astounding.
Stars in the new images from the James Webb Space Telescope look sharper than they did before.