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  • When you ask someone to draw a star, they'll probably draw something like this - or this

  • or this. Even ignoring the rainbows, this doesn't seem very scientific, since we know

  • stars are actually big hot ROUND balls of plasma and far enough away that they're basically

  • just dots. So why do we draw stars that have points?

  • The answer is surprisingly simple: we see stars as pointy. Look carefully next time

  • you're outside on a dark night - or just look at this dot (it works best if you make the

  • video fullscreen, close one eye, and relax the other as if you're looking at something

  • far away). You should see a pointy, star-like shape! In fact, it's not just humans that

  • see pointy stars - some telescopes see them that way, too!

  • This is all because light is a wave. When light from a distant source passes through

  • an opening or around an object, its waves are bounced or bent slightly and interfere

  • with each other, so the passing light picks up an imprint of that opening or object. A

  • straight line (whether it's a slit letting light through or a rod blocking the light)

  • leaves its imprint by spreading the light out into a perpendicular series of dashes

  • (- like what you see when you squint!) A cross creates two, perpendicular, sets of dashes,

  • circles cause concentric rings, squares spawn a kind of dashed four-pointed star, hexagons

  • dashed six-pointed stars; and the famous double slit experiment gives a series of dashed dashes.

  • My favorite diffraction pattern, though, is probably that of the Penrose tiling - it's

  • simply gorgeousnot that you see Penrose-tiling-shaped openings very often. Butthe point of all

  • of these imprints is that they're the result of a point of light being spread out when

  • viewed through a particular opening or past a particular object.

  • For example, the Hubble space telescope has four struts that support its small secondary

  • mirror, and their imprint causes the 4-pointed stars in hubble photos. And I bet you can

  • guess the shape of the aperture on the lens that took this picture. Similarly, the lenses

  • of our eyes have subtle structural imperfections called suture lines where the fibers that

  • make up the lens meet. These imperfections leave a very particular imprint on light as

  • it passes by, as researchers have confirmed by shining lasers in people’s eyes.

  • So, even though stars themselves are just tiny round dots, by the time the light reaches

  • our retina, it's been smeared out into a starlike shape. Every single eye on earth will see

  • a slightly different starlike smear depending on the exact nature of its suture lines - even

  • your left and right eyes will differ! What's weird, though, is that any particular eye

  • sees the same shape for every star - so while it is scientifically acceptable to draw stars

  • like this, if you draw more than one in a single picture, you better make sure they're

  • all the exact same shape!

  • On top of that, since diffraction spreads longer wavelength red light out more than

  • bluer light, the arms of these star-shapes are actually mini-rainbows with red on the

  • outside and blue in the middle! Which, again, you can see in hubble photographs or if you

  • look even more carefully at a single point of light. So as crazy as it sounds, coloring

  • in stars with rainbows is super scientifically accurate - as long as the colors go the right

  • way.

When you ask someone to draw a star, they'll probably draw something like this - or this

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