The EMS is all the radiation that exists. The radiation that our eyes can see is called the visible spectrum. Other parts of the EMS occur outside this region and we must build special instruments to detect them. The EMS radiation (both visible and invisible) is characterized by wavelength and frequency. The broad range of radiation is grouped into general spectral regions based on their wavelength and frequency.

Students often come up with a mnemonic phrase to remember this sequence.One such phrase is: Rosa’s Mom Invited Very Ugly Xmas Guests. Here’s another one: A Radioactive Monkey is Very Interesting and eXtremely Goofy.

You can do better than these!The EMS is traditionally divided into the categories of:

Radio

Microwave

Infrared

Visible

Ultraviolet

X-rays

Gamma rays

 

 

In this chart the wavy line at top shows that wavelengths are short at the gamma ray end of the spectrum, and long at the radio end. The light blue wavelength arrow shows that and gives the lengths of some representative wavelengths in meters. You notice that all wavelengths except radio waves are shorter than a meter in length, in fact, many are shorter than a millionth of a meter.  The bottom pictures show things that are about the size of the different wavelengths – from football fields to the nucleus of an atom.