Here are kitten tracks in the infrared:

What’s infrared? It’s a type of light too “low” for us to see… Some sounds are too low for us to hear because our ears only pick up a certain range of pitches (determined by the frequency of sound waves), infrared light is a color with a frequency too low for our eyes to see.

The temperature of a thing determines the color of light that it emits (or, the spectrum of its radiation). Relatively cool objects, like people, emit mostly infrared light. Things that are hotter than people — like coals and lightbulbs — emit visible light. That’s why coals and lightbulbs and flames look bright to us — they’re emitting a lot of light that we can see. Even hotter things, like stars, emit mostly ultraviolet light and x-rays, which is how some astronomical observatories see them.

Some animals (like snakes) do see in the infrared. That’s helpful because most living things emit infrared light, not visible light. The warmer they are, the more infrared light they give off. (Infrared isn’t equivalent to heat, contrary to what I say in the video. Hey, I was in the spotlight and made a mistake. :-).

You can’t see in the infrared, but your digital camera can. Point the end of your remote control at your digital camera and press the button while you’re looking through the viewfinder. You will see a flashing light — your remote control emits in the infrared, and your digital camera sees it.

Your digital camera doesn’t act like a heat sensor camera, though, because it only sees in the “near infrared” — a part of the infrared that’s pretty close to visible red. Firefighters use cameras that see in the “far infrared,” a range of frequencies far below the visible, in order to find people in burning buildings. That’s the kind of camera we have in the Exploratorium, as in the video below.

Here I am in the infrared

And a rubber band gets hot when stretched!