20
BY GEMMA TARLACHRainbows
THINGS
YOU
DIDN’T
KNOW
ABOUT...74 DISCOVERMAGAZINE.COM
on expectations, which are the product of culture.
Aristotle, for example, wrote of only three colors in the
rainbow: red, green and violet. 12 Some early Islamic
scholars also saw a tricolored rainbow, but it was red,
green and yellow. Medieval proto-scientist Roger
Bacon described five colors; so did early Chinese
scientists and philosophers. 13 Only after Sir Isaac
Newton, in the 17th century, linked perceived colors
in a rainbow to notes on a Western musical scale did
European scientists agree that there were seven colors.
14 Something else to note: A rainbow will always be
opposite the sun. If you think you’ve spotted one near
or around our day star, you’re seeing something else.
15 Parhelia, also known as sundogs, may appear as
rounded or spiky arcs on either side of the sun. Halos,
meanwhile, circle the sun. Both phenomena result
from hexagonal ice crystals in high-altitude clouds
acting as prisms. 16 Fire rainbows have nothing to do
with rainbows, either. (Or with fire, for that matter.)
More accurately known as circumhorizontal arcs, they
appear horizontally and are another product of high-
altitude ice crystals refracting light. 17 Fire rainbows
should also not be confused with the flaming rain-
bow bridge of Norse mythology. That rainbow, called
Bifröst, joined the mortal world with that of the gods.
Upon death, worthy souls would cross it into Valhalla.
18 The Bifröst myth is likely the inspiration for a
certain modern folk tale: When beloved pets die, the
story goes, they cross the Rainbow Bridge to an idyllic
place where they await their owners. 19 Pet lovers and
Vikings aren’t the only ones to see rainbows as a con-
nection between the worlds of the living and the
dead. In fact, the legend of Bifröst may be rooted in
the rainbow pathway traveled by Greek and Roman
messenger goddess Iris. 20 Other, even older Asian
and Native American traditions also see the colorful
arc as linking our world with another. Science may tell
us that rainbows are roads to nowhere, but worldwide
their allure endures — for the lovers, the dreamers
and me.^ DSenior editor Gemma Tarlach wishes the “Rainbow
Connection” a happy 40th anniversary.1 Why are there so many songs about rainbows? It
could be because the meteorological phenomena,
beautiful yet ephemeral, inspire our inner romantics.
Or maybe it’s because no one sees the same rainbow.
2 Imagine a line from the sun, which will be some-
where behind you, through the back of your head
and out your eyes, ending at the shadow of your head
on the ground. Any rainbow you see will be centered
around that axis. 3 Someone standing beside you may
also see a rainbow, but it will
be around an axis running
from the sun to their head
shadow. 4 Rainbows occur
when sunlight — including
all wavelengths of visible
light, which together appear
as white light — pinballs in
and out of water droplets
(usually rain, but some-
times water spray, or the
droplets that form mist or
fog). 5 Some of the light is
reflected off the drop’s outer
surface, but the rest of it
enters the droplet, skidding as it does so. 6 This skid,
or refraction, occurs because water is denser than air.
As the light enters the droplet, it slows and changes
direction. (Think of what would happen if you were
speeding along the freeway, and the asphalt suddenly
turned to mud.) 7 Once inside the droplet, the light
reflects off the back inner surface, then refracts a
second time, bending as it travels out of the water and
back into the air. 8 Because the droplet is spherical and
its surfaces are not parallel, all this skidding in and out
happens at slightly different angles for the different
wavelengths of visible light, so the exiting white light
disperses into a spectrum of colors. 9 The gradation of
color in a rainbow is continuous — there are no stripes.
Humans, however, like to organize things, including
colors, to make sense of them. 10 Researchers think
that’s why our brains divide the bow’s spectrum into
distinct bands. The exact mechanism for seeing
stripes, and whether it’s purely in the brain or also
in the eye, remains unknown. 11 The number of
colors an individual perceives in a rainbow depends
DISCOVER (ISSN 0274-7529, USPS# 555-190) is published monthly, except for combined issues in January/February and July/August. Vol. 40, no. 4. Published by Kalmbach Media Co., 21027 Crossroads Circle, P.O. Box
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53187-1612.Printed in the U.S.A.From top: Printed
rainbows have
stripes, but real
rainbows don’t —
their color gradation
is continuous; in
Norse mythology,
Bifröst was a rainbow
bridge to the gods;
phenomena such as
parhelia and halos
are beautiful, but
they’re not rainbows.
Refraction
splits white light
into a spectrum
of colors.COUNTERCL
OCKWISEFROMTOP^ RIGHT:^ PETRROUDNY
43
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