#diffraction spikes

Even if a planet is lucky enough to have a stable orbit that weaves between the spikes, the seasons get weird whenever it passes close to them.

"Webb's Diffraction Spikes Extended Description

This is a diagram labeled “Webb’s Diffraction Spikes”. The top right of the image shows three stars producing eight-pronged diffraction spike patterns. This diagram is composed of five sections.

The first section is headlined “What Are Diffraction Spikes?” Below the headline is a caption that says, “Have you ever noticed that bright stars in your favorite space images have unique spikes around them? These are known as diffraction spikes. Diffraction spikes are patterns produced as light bends around the sharp edges of a telescope. While all stars can create these patterns, we only see spikes with the brightest stars when a telescope takes an image. For most reflecting telescopes, including Webb, diffraction spikes appear when light interacts with the primary mirror and struts that support the secondary mirror.” Below this is an image of Webb’s observing side, including its 18 gold hexagonal segments, science instruments, primary mirror, struts and secondary mirror.

The second section is headlined “How Does Diffraction Happen?” Underneath this headline is a caption that says, “Light, which has wave-like properties, tends to radiate from a central point outward, similar to how water behaves when a stone is tossed into it. As light encounters an edge, it is bent and redirected, sending it in different directions. In situations where these light waves meet and interact, they can either become more amplified or cancel each other out. These areas of amplification and cancellation form the light and dark spots that show in diffraction patterns.” Underneath this caption are two boxes, lined horizontally. The first box, on the left, is a star that displays Hubble’s Diffraction Pattern, which has four-points – two vertical and two horizontal points. The second box, on the right, is a star that displays Webb’s Diffraction Pattern, which has eight-points – two vertical, two horizontal and four diagonal points.

The third section is headlined, “Primary Mirror Influence”. Underneath this headline is a caption that says, “Primary mirrors in reflecting telescopes cause light waves to interact as they direct light to the secondary mirror. So, even if a telescope had no struts, it would still create a diffraction pattern. The shape of the primary mirror, in particular the number of edges it has, determines the mirror’s diffraction pattern. Light waves interact with those edges to create perpendicular diffraction spikes.” Underneath this caption are six images, broken into rows of three. The first three are labeled, “Primary Mirror Shape”, which display a circle, square and hexagonal shape, like Webb’s, in white. The last three are labeled, “Image of Point Source”, and display the patterns due to the “Primary Mirror Shape” underneath. The first displays a diffraction pattern with a solid, bright center and alternating dark and light circles. The next shows a six-pointed spike pattern with alternating bright and dark regions. The last shows a complex fractal of light and dark regions within eight spikes – the closest representation to Webb’s.

The fourth section is headlined, “Strut Influence”. Underneath this is a caption, which describes the graphic below it, and says, “The number and position of struts holding up the secondary mirror determine the struts’ diffraction spike pattern. In the first row, there is a set of struts organized in a single line. When light hits a strut, the light bends into a single, perpendicular pattern of amplified and cancelled light (represented by a yellow dashed line). In the second row, a second set of struts is added to the first, creating a second, perpendicular diffraction spike (represented by a red dashed line). In the third row, there are three struts with two of them at an angle. In this case, there would be three diffraction spikes, with each spike perpendicular to a strut (represented by yellow, red, and blue dashed lines).”

The last section is headlined, “Webb’s Eight-Pointed Stars”. Underneath the headline is a caption that says, “Like most reflecting telescopes, the diffraction spikes for Webb are defined by its primary mirror and struts. Webb has three struts, with two angled at 150 degrees from its vertical strut, and its primary mirror is composed of hexagonal segments that each contain edges for light to diffract against. Webb’s struts are designed so that their diffraction spikes partially overlap with those created by the mirrors. Both of these lead to Webb’s complex eight-pointed star pattern.” At the bottom of this diagram is Webb’s eight-pointed star pattern organized by its “Strut Influence”, which overlaps parts of the star with red borders, and its primary mirror influence, which overlaps parts of the star with yellow borders. Above this image are more images that show the Webb’s segmented primary mirror and struts, with the primary mirror’s borders highlighted yellow and its struts highlighted red."

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NASA, ESA, CSA, Leah Hustak (STScI), Joseph DePasquale (STScI)

i know the photos themselves are what's making the rounds but i want to share this infographic on the unique star twinkle from jwst photos. Even something like this was tweaked to be optimized!

The cool star shapes were one of the first things that caught my attention so i'm glad there's an in-depth and layperson friendly explanation.

NGC 6717 - Globular Cluster

This massive group of stars form what is known as a globular cluster. Most are ancient 12-13 billion years old and there are around 150 of them known in the Milky Way.

NGC 6717 is one closer to the galactic centre, around 23,000 light years from us in the constellation of Sagittarius. Not all the stars in this recent Hubble image are from the cluster, rather, they are much closer to us and just sit in the foreground. You can tell which are closest by observing the cross like diffraction spikes generated by imperfections in the Hubble mirrors.

World's Largest Telescope To Finally See Stars Without Artificial Spikes

“Compared to what we can presently see with the world's greatest observatories, the next generation of ground-based telescopes will open up a slew of new frontiers that will peel back the veil of mystery that enshrouds the unseen Universe. In addition to planets, stars, gas, plasma, black holes, galaxies, and nebulae, we'll be looking for objects and phenomena that we've never seen before. Until we look, we have no way of knowing exactly what wonders the Universe has waiting for us. Owing to the clever and innovative design of the Giant Magellan Telescope, however, the objects we've missed due to diffraction spikes of bright, nearby stars will suddenly be revealed. There's a whole new Universe to be observed, and this one, unique telescope will reveal what no one else can see.”

When we take images of the Universe, we are so used to seeing the sight of spikes around the stars in our own galaxy, it frequently doesn’t even occur to us that stars are near-perfect spheres, without any spikes to them at all. These are simply image artifacts created by reflecting telescopes, since they require a secondary mirror to collect and focus the light that the primary mirror reflects. These secondary mirrors are held in place by “spider arms,” which cross the plane of the mirror and block some of the light, creating these diffraction spikes. Up until now, these spikes were unavoidable, and the best we could do was using imaging techniques to try and subtract them out. But due to a brilliant design feature, the upcoming Giant Magellan Telescope, due to be the world’s largest (for a time) at 25 meters, will be the first giant reflector to image the stars exactly as they are: without these spikes at all.

Diffraction spikes

Stars are spherical balls of mostly hydrogen, but we do not draw stars as circles, and when we view them or take pictures of them, they appear to have spikes of light emanating from the star. 

These spikes are an optical illusion known as Diffraction spikes, caused by the imperfect way we view or record them.