WARNING - Don't be confused!

Waves longer than 10cm can be called radio waves.   

That said, classifying E.M. waves is a very artificial system .   Radio astronomers also use shorter wavelengths in the microwave region. Many would claim that microwaves are radio waves.   On the other hand the infrared astronomers would  claim some of them as the far infrared.   That's because the properties of infrared and radio overlap in this region of the spectrum.   If you do an internet search on the range of each region you will find very little agreement.   Some scientist like 30cm as the lower limit of radio waves.  Others (usually astronomers) don't bother with microwaves at all and call everything up to infrared, radio.

The Radio Window

 Microwaves could be said to have a wavelength between 1mm and 1cm (or 3mm -30cm for some) and most of them  have a problem with water - it absorbs them.   This is great if you want to heat up a curry (12 cm waves in your oven) but bad news if you want to use them to image something that is the other side of the atmosphere, because even a cloudless sky is full of water particles.  

Wave absorption by water is a particular problem to astronomers studying  the microwave background.   These  signature wavelengths of the Big Bang peak at about 1mm, just right to be almost blocked by the atmosphere.      

Waves that are longer that 1cm and up to 20m waves are able to penetrate the atmosphere.   Waves longer than that are bounced off an upper layer of the atmosphere called the ionosphere.   So wavelengths between 1cm and 20m are able to get through the 'radio window' of the Earth's atmosphere.   If you want to use radio wavelengths greater than 20m you'll need to launch a satellite!  

Despite the general blocking of wavelengths between the violet end of the visible spectrum and 1cm, there are lots of little windows at specific wavelengths.   Wherever a window exists, there are astronomers with special telescopes peering through it.   A great example of this is the James Clerk Maxwell Telescope (JMCT) on top of the Mauna Kea volcano in Hawaii.   Here scientists look at the so called sub-millimetre waves between 0.3mm to 1mm and other wavelengths up to 2mm.   Their instrument is a cross between a radio telescope with a 15m dish, and an infrared telescope with a detector cooled to 3^oK (-270^oC)

So the difference between an infrared astronomer and a radio astronomer should be that the infrareds would like satellite observatories whilst radios would like big dishes on Earth.   Except most radio astronomers would prefer their dishes on the far side of the Moon.   This is because despite the international protection of certain frequencies for astronomy, astronomers monitoring cosmic radio waves often have to try to filter out Kylie's latest single!

 If you have a go at radio astronomy, the wavelengths that you will use are around 14m.   Radio waves  are normally identified as frequencies rather than wavelengths so to convert just divide the wavelength into the speed of light.   So that's 300 million metres per second divided by 14 which comes out at about 21 million waves per second or 21MHz (Mega Hertz).

If you fancy looking at infrared then  NASAs Infrared Processing and Analysis Centre (IPAC) is the place to go to find out all about it.   Also the biggest telescope in the world dedicated to IR observing is the United Kingdom Infrared Telescope (UKIRT).   Nice to know we have the biggest something!  Club members who fancy having a go in this region should have a word with me - we can get some film for recording the near infrared.

So don't get too worried about which region you are in.  Just be sure of your wavelengths and frequencies!