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 gorgeous… not that you see Penrose-tiling-shaped openings very often.
But… the 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.
