Original subtitles

The sunlight that falls on our earth

warms the palms of our hands slightly.

Let's try an experiment with sunlight.

After blacking out the window with curtains, we make a thin slit to let in the sunshine

and place a prism in the light's path.

The ray splits into many colors like a rainbow.

This is called the visible light spectrum. It shows that sunlight contains various colors of light.

Let's move on to the next step.

We place an array of thermometers on the screen, covering each probe with black film, to see how they heat up.

After about 3 minutes, some differences appear.

The top thermometer marks 24°C in the shade, and

the next two are 25°C.

As we move down, the temperature rises.

The thermometer under the red light shows 27°C.

Apparently, the ability to heat varies depending on the light color.

But we should be paying attention to the bottom one.

Even though it is in the shade,

somehow it marks 26°C, just above the averaged value.

What exactly is happening here?

When sunlight passes through a prism, violet light, which has a short wavelength, bends a lot,

while red light, which has a long wavelength, bends less.

The rainbow color spectrum appears because this bending behavior depends on the color, or wavelength.

However, sunlight does not consist only of visible light.

It also contains infrared and ultraviolet rays.

Infrared light has a longer wavelength than red light.

Thus, the infrared light must be concentrated

in this area, just below the red bar.

Let's view this spectrum with an infrared camera.

When we point below the border of the red bar with tweezers,

this area is illuminated in the infrared view.

Yes, this is infrared light.

When we look at the thermometer array through this infrared camera,

we clearly see that the thermometer at the bottom is also irradiated by infrared light.

The bottom thermometer is being heated by invisible infrared rays.

Let's try another experiment.

Place a board with a square hole by the window.

On the desk, there is a rectangle of sunshine passing through the hole.

Next, let's cover this hole with a black sheet.

The light on the desk disappears, but

when you hold your palm near the cover, you feel warmth without any visible irradiation.

When we look at this setup through the infrared camera,

we can see a bright rectangle of light.

It looks like only the infrared rays penetrate the black cover.

In fact, the cover is not a shield that blocks sunlight, but

a filter that allows infrared rays to pass through.

When we put a hand into these invisible rays,

look, a silhouette appears.

This is because the hand blocks the path of infrared light, isn't it?

Indeed, it's slightly warmer there.

Is it possible to concentrate

these infrared rays with a magnifying glass like ordinary light?

Let's try it.

Place a piece of black paper into the light path of the infrared rays, and

hold a magnifying glass over it.

What happens when we concentrate the infrared rays on the paper?

After a while,

the paper starts to burn with a trail of smoke.

Of all the sun's radiation, red light and infrared light are the best at heating things up.

Even though infrared rays are invisible, when concentrated with a lens, they can burn paper.

This world is full of invisible things and events.

If we can find the key to see them, we can open the door to a new world.

A message to the scientists of the future,