The Electromagnetic Spectrum
Here’s a great explanation of the Electromagnetic Spectrum from NASA.
Here’s a great explanation of the metric system from the US Metric Association.
Here’s a great visual that compares the size of the wavelengths to everyday items.
You can click on the image below to download an 8-1/2″ x 11″ JPG of the chart. Or click here for a PDF
[Here’s a Romanian translation of this web page done by an interested party.]