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.
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.