>> Let's look in more detail at heat energy or the thermal radiation that
results from objects at room temperature or planets or people.
This is a familiar regime in astronomy, because we will be looking at
Planetary Science and cool objects adjacent to stars.
These objects will emit infrared radiation and
because we have the technology to make images with infrared radiation, it's clear
that we can view infrared radiation in the same way that we view visible light.
[SOUND].
>> These days, we're all familiar with night vision cameras, but
how do these things work?
How is it that you can just turn on this camera and see the invisible?
[SOUND] Another use of night vision cameras that you might not be
familiar with is their ability to see through smoke and dust.
Fire departments commonly use cameras like these to find people trapped in smokey
rooms or to pinpoint the exact location of forest fires through clouds of smoke.
[SOUND] So how do these things actually work?
What are we really seeing when we look inside a night vision camera?
Well, it may surprise you to learn that everything in the universe emits some kind
of light.
It's just not the kind of light we're used to thinking about.
The sun, for example, our star emits visible light.
That's why our eyes evolved to detect that kind of light, but
that's not the whole story.
I'm sure you're familiar with all the different kinds of visible light,
all the colors from violet to red.
But there are actually lots of other kinds of light that our
eyes aren't sensitive to.
The reason all the colors of light are different is that they have different
energies and what you see here is that the light has different wave lengths.
The blue light, for example, has a higher energy, so it has a shorter wavelength.
The red light on the other hand, has less energy, so it has a longer wavelength.
But that's just the light we can see with our eyes.
That's not all there is.
The shortest wavelength lite are gamma rays,
which can have wavelengths smaller than an atom.
The longest wave lengths are radio waves,
which can have wave lengths larger than the entire earth.
[NOISE] The kind of light an object omits depends on its temperature.
We're used to thinking of something hot giving off light, but
it might surprise you to learn that objects that are cooler, like myself,
give off a kind of light too and that's what a night vision camera can pick up.
That sort of light is called infrared light.
[MUSIC]
The world sure looks a lot different in infrared light.
Remember that what you're actually seeing is temperature.
Something that's warm [NOISE] is going to look bright in the infrared.
[NOISE] And something that's cold looks dark.
Ice cream.
Blow dryer.
[NOISE] And infrared radiation is actually a measurement of temperature.
Places on my face that are cold like my nose, appear dark in infrared camera,
because they're giving off less infrared radiation.
And places that are warm, like my mouth or
the hair next to my head are brighter, because they're warmer.
You can even see my breath in my nose, if you look carefully.
[SOUND] And this is an ice cube.