what if you could only see one color
imagine for instance that you could only
see things that were red and that
everything else was completely invisible
to you as it turns out that's how you
live your life all the time because your
eyes can only see a minuscule part of
the full spectrum of light different
kinds of light are all around you every
day but are invisible to the human eye
from the radio waves that carry your
favorite songs to the x-rays doctors
used to see inside of you too the
microwaves that heat up your food in
order to understand how these can all be
light we'll need to know a thing or two
about what light is light is
electromagnetic radiation that acts like
both a wave and a particle light waves
are kind of like waves on the ocean
there are big waves and small waves
waves that crash on the shore one right
after the other and waves that only roll
in every so often the size of a wave is
called its wavelength and how often it
comes by is called its frequency imagine
being a boat in that ocean bobbing up
and down as the waves go by if the waves
that day have long wavelengths they'll
make you Bob
only so often or at a low frequency if
the waves instead have short wavelengths
they'll be close together and you'll bob
up and down much more often at a high
frequency different kinds of light are
all waves they just have different
wavelengths and frequencies
if you know the wavelength or frequency
of a wave of light you can also figure
out its energy long wavelengths have low
energies while short wavelengths have
high energies it's easy to remember if
you think about being in that boat if
you are out sailing on a day with short
choppy waves you'd probably be pretty
high-energy yourself running around to
keep things from falling over but on a
long wavelength sea you'd be rolling
along relaxed
low energy
the energy of light tells us how it will
interact with matter
for example the cells of our eyes when
we see it's because the energy of light
stimulates a receptor in our eye called
the retina our retina are only sensitive
to light with a very small range in
energy and so we call that range of
light visible light inside our retina
our special receptors called rods and
cones the rods measure brightness so we
know how much light there is the cones
are in charge of what color of light we
see because different cones are
sensitive to different energies of light
some cones are more excited by light
that is long wavelength and low energy
and other cones are more excited by
short wavelength high-energy light when
light hits our eye the relative amount
of energy each cone measures signals our
brain to perceive colors the rainbow we
perceive is actually visible light in
order of its energy and one side of the
rainbow is low-energy light we see as
red and at the other side is high-energy
light we see as blue
light shines on us that has an energy or
retina can't measure we won't be able to
see it light that is too short
wavelength or high energy gets absorbed
by the eyes surface before it can even
get to the retina and light that is too
long wavelength doesn't have enough
energy to stimulate our retina at all
the only thing that makes one kind of
light different from another is its
wavelength radio waves have long
wavelengths while x-rays have short
wavelengths and visible light the kind
you can actually see is somewhere in
between even though our eyes can't
detect light outside of the visible
range we can build special detectors
that are stimulated by these other
wavelengths of light kind of like
digital eyes with these devices we can
measure the light that is there even
though we can't see it ourselves
so take a step back and think about all
of this for a moment even though they
seem different the warmth you feel from
a crackling fire is the same as the sun
shining on you on a beautiful day the
same as ultraviolet light you put on
sunscreen to protect yourself from the
same thing as your TV your radio and
your microwave
now those examples are all things here
on earth things you experience in your
everyday life but here's something even
more amazing our universe gives off the
full spectrum of light - when you think
of the night sky you probably think of
being able to see the stars shining with
your own eyes but that's just visible
light which you now know is only a tiny
part of the full spectrum if we had to
draw the universe and could only use
visible light it would be like having
only one crayon pretty sad to see the
universe in its full spectrum we need to
have the right eyes and that means using
special telescopes that can help us see
beyond visible light you've probably
heard of the Hubble Space Telescope and
seen it's beautiful pictures taken in
visible and ultraviolet light but you
might not know that there are almost 20
space telescopes in orbit missions that
can each see part of the full spectrum
of light with telescopes acting as our
virtual eyes both in space and here on
earth we can see some amazing things and
the coolest thing of all
no matter the wavelength or energy the
light that we see out in the distant
universe is the same thing as the light
that we can experience and study here on
earth
so since we know the physics of how
x-ray ultraviolet light or microwaves
work here we can study the light of a
distant star or galaxy and know what
kinds of things are happening there - so
as you go about your daily life think
beyond what your eyes can and can't see
knowing just a little bit about the
natural world can help you perceive the
full spectrum around you all the time
Oh