Ray Tomes wrote:
My questions:

Has any observation been made below 10^6 Hz of the general
background spectrum?

[[Mod. note -- I think very little radio astronomy of any kind has been
done at such low frequencies. Indeed, I'm not even sure if the Earth's
ionosphere is even transparent at 1 MHz frequencies; if not, the
observations would have to be done from space. Try searching on the
ADS or scholar.google.com for 'low frequency radio astronomy'. -- jt]]

Even more specifically, check on "Radio Astronomy Explorer", also
known as Explorer 49, which unfurled two quite long dipoles
in lunar orbit (a few thousand km of rock does manage to block
all that nasty emission from stuff om the geomagnetic field).
If I read an NRL page correctly, it did measurements down to about
250 kHz, while below 30 kHz, the ISM absorbs the radiation. (That
might limit how much ambient density you could have at the lowest
frequencies, but this is a radiative-transfer regime I'd be bound
to screw up on the back of an envelope).


Bill Keel