The other day in class, I was explaining how the photogates for the physics equipment work.  They use infrared light, which is light that is just outside of the wavelengths of light that human eyes can see.  The electromagnetic spectrum below shows all the different types of electromagnetic energy, or light, in the universe.

Visible light, or the light that we can see, is in the center of the spectrum.  Human eyes can see light with wavelengths from 400 to 700 nanometers.  Infrared is just to the left.  It is light that has wavelengths a bit longer than 700 nm.  All objects give off infrared radiation; the hotter the object, the more infrared is given off.  Some organisms, like pit vipers, boa constrictors, and some insects, can see infrared.  We have developed ways to make infrared visible, with special cameras and film. 

This photo shows the infrared radiation emitted by a dog.

 

The sun emits all the radiation in the spectrum.  The atmosphere, including the ozone layer, prevents much of the radiation from reaching the surface of the earth.  Nonetheless, we are daily bombarded with X-, gamma, radio, ultraviolet, and microwaves.  Although we cannot see them, we can detect their presence.  One detector that we all carry with us is our skin, which tans, freckles or burns (depending on our genetic makeup) in response to exposure to ultraviolet radiation.

 

This got me started thinking about how there is so much around us that we cannot see.  It is amazing that there is an entire universe that exists outside of our range of vision!  For example, a drop of pond water may at first glance look similar to a drop of tap water.  However, it contains tiny one-celled creatures that go through their lifespans unobserved by us.  Even smaller than these creatures are bacteria and viruses.  Of course, everything around us, including these bacteria and viruses, are made of molecules, built of atoms bonded together in particular patterns to make all known matter.  If this isn't mind-boggling enough, they tell us that atoms themselves are made of even smaller particles; electrons, protons, neutrons, quarks, gluons and neutrinos!  The electricity that powers the laptop that I am using is created from the kinetic (moving) energy of electrons!