On Aug 30, 8:03 am, Margo Schulter wrote:

It's interesting question how radio and infrared astronomy are
distinguished: mainly by the nature of the waves, or also by
the apparatus used. I'd like to to learn more of this myself.

Again, I'd emphasize that in giving the range for EHF, I'm not
saying that anything above 300 GHz wouldn't be considered radio,
only mentioning this category as an example of what was
traditionally considered near the top of the radio spectrum.

Maybe Laura or others could comment more expertly on this.

The ITU definition of "radio" ends at the top of EHF, at 300 GHz.
However, this is more a reflection of the technical state of the
art at the time the definition was made. Earlier definitions ended
at 30 GHz, or even lower. I've read papers in journals for radio
equipment that operates above 400 GHz. You need a microscope
to inspect the components. :-)

Above 300 GHz is no man's land, in that no radio license is
required to send signals. Laser communication links are
not licensed as radios; they are not generally licensed at all,
unless health & safety officials take an interest in the lasers
themselves.

The spectrum between EHF and infrared is viewed as not useful
for communication, because the atmosphere is more-or-less
opaque at these wavelengths. But that's what they said about
frequencies about 30 MHz in the 1920s, too. And in space, who
cares?

The usual agreement is that it's radio astronomy when the
incoming signals are electronically detected (e.g. diodes) and
processed. It's optical/infrared astronomy when the incoming
signals are measured by a bolometer or other non-electronic
means. There is, naturally, some crossover.

Laura Halliday VE7LDH "Non sequitur. Your ACKS are
Grid: CN89mg uncoordinated."
ICBM: 49 16.05 N 122 56.92 W - Nomad the Network Engineer