Bill Otten wrote:

Not necessarily. The planet Jupiter emits a signal that can be heard at
about 15 meter wavelength, about 21 mhz or so. That signal penetrates the
ionosphere pretty nicely. See
http://radiojove.gsfc.nasa.gov/libra...discovery.html for more
info...

bill
KC9CS

Receiving the 21-Mhz HF (shortwave) energy from Jupiter depends on it's
altitude above the observer's local horizon and the MUF (maximum usable
frequency) for the particular area of the ionosphere where the signal is
trying to penetrate to the ground. In the first case, when Jupiter is
near the horizon, it's radio signal may not penetrate the ionosphere
because of the shallow incident angle. The energy is refracted off the
top of the ionosphere back into space like skipping a stone on water. In
the second case, if the local MUF is too high, it won't allow the 21-Mhz
energy to penetrate to the ground from space regardless of the incident
angle.
The best time to radio observe Jupiter is when the conditions are the
opposite of the first two cases above, or particularly when it's high in
the sky at night. This is when the signal passes through the ionosphere
at a more vertical angle to the observer (no skipping) and the local MUF
is at it's lowest for the day, which happens some time after sunset.
It's also best when the solar flux is low, near sunspot minimum, as it
is now. This insures a low MUF (well below 21-Mhz) so Jupiter's signal
can reach the surface of the earth more often.

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