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Observation of ELF etc in universe?



 
 
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  #1  
Old May 4th 05, 11:42 AM
Ray Tomes
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Default Observation of ELF etc in universe?

First some background and then a question or two.

Some years ago I had a debate with Ted Bunn concerning the stated
411 photons/cm^3 in the universe. I maintained that the no. of
photons at low frequencies (ELF ULF etc) probably vastly exceeds
the CMBR count of 411.

Ted was totally dismissive until he saw the graphic at
http://ray.tomes.biz/ref-back.gif
from "Cosmology" by Michael Rown-Robinson page 100 after
which he agreed that it was possible but said that he still
thought that I was wrong.

The graph shows that below about 10^9 Hz the intensity of the
universal background again begins to rise through to 10^6 Hz
where the graph finishes.

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]]

I saw a TV interview with an Australian radio astronomer who
said that he was studing low frequency and that the sky was
as bright as the Sun all over. Unfortunately I didn't get his
name and the frequency range wasn't mentioned.

What do other people think when they look at this graph?
It rises by 16 orders of magnitude as the frequency reduces
by 18 orders of magnitude. It looks like a general trend to me
with a few bumps on - CMBR, effect of dust etc. - although
admittedly the CMBR is a big bump.

Do others see the possibility that from 10^6 Hz through to
10^-17 Hz it could rise at the same average rate and reach
10^20 times as many photons as in the CMBR. Of course the
much lower energy per photon would mean that the total energy
is not increasing by that much, but it could still be a
significant contribution to dark matter.

--
Ray Tomes
http://ray.tomes.biz/
http://www.cyclesresearchinstitute.org/
  #2  
Old May 4th 05, 02:04 PM
William C. Keel
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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
  #3  
Old May 5th 05, 11:32 AM
Oz
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Our esteemed moderator writes

Mod. note -- I think very little radio astronomy of any kind has been
done at such low frequencies.


The amount of artificial radio (communication) noise would be utterly
overwhelming...

Indeed, I'm not even sure if the Earth's
ionosphere is even transparent at 1 MHz frequencies;


Medium wave...

The ionosphere is reflective which is why medium wave has very long
range as it bounces between earth and sky.

However I think long wave (200kHz or so) is transparent since the range
is about a wavelength or so. Originally this was chosen because it was
expected to get some 'diffraction over [under] the horizon'.

VLF circa 10-20kHz is used for very long range submarine communication
(one way) since it penetrates 'quite deeply' into seawater. I think many
repeater stations are required so presumably the ionosphere is
transparent here too.

I believe a radio telescope for these frequencies has been proposed,
on the far side of the moon.

--
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This post is worth absolutely nothing and is probably fallacious.

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  #4  
Old May 5th 05, 11:32 AM
Jonathan Silverlight
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In message , Ray Tomes
writes
First some background and then a question or two.


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]]


The Voyager planetary radio astronomy experiment apparently covered the
range 1.2 kHz to 1.228 MHz
http://www.igpp.ucla.edu/pds2/VG_1601/DOCUMENT/PRA/PRAINST.HTM.
I see Bill Keel has noted the Radio Astronomy Explorers and absorption
in the ISM; I'll just comment that the absorption is mentioned in Arthur
Clarke's novel Imperial Earth, where this LF astronomy plays a
significant role.
--
mail to jsilverlight AT merseia DOT fsnet DOT co DOT uk is welcome.
  #5  
Old May 5th 05, 11:33 AM
Joseph Lazio
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"RT" == Ray Tomes writes:

RT Some years ago I had a debate with Ted Bunn concerning the stated
RT 411 photons/cm^3 in the universe. I maintained that the no. of
RT photons at low frequencies (ELF ULF etc) probably vastly exceeds
RT the CMBR count of 411.

RT Ted was totally dismissive until he saw the graphic at
RT http://ray.tomes.biz/ref-back.gif from "Cosmology" by Michael
RT Rown-Robinson page 100 [...]

RT The graph shows that below about 10^9 Hz the intensity of the
RT universal background again begins to rise through to 10^6 Hz where
RT the graph finishes.

RT My questions:

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

As Bill Keel has pointed out already, there have been space-based
observations below 1 MHz. There were actually two Radio Astronomy
Explorers. Also, there have been any number of spacecraft observing
either the Sun or the planets that have made observations below 1
MHz.

[...]
RT What do other people think when they look at this graph? It rises
RT by 16 orders of magnitude as the frequency reduces by 18 orders of
RT magnitude. It looks like a general trend to me with a few bumps on
RT - CMBR, effect of dust etc. - although admittedly the CMBR is a
RT big bump.

RT Do others see the possibility that from 10^6 Hz through to 10^-17
RT Hz it could rise at the same average rate and reach 10^20 times as
RT many photons as in the CMBR.

No. Below a certain frequency, the waves cannot propagate. The
interstellar (and presumably intergalactic) medium has a plasma
frequency, given by 9 kHz*\sqrt{n_e} where n_e is the electron density
in units of cm^{-3}. In the local interstellar medium, n_e ~ 0.025
cm^{-3}, so waves with frequencies below 1 kHz just don't propagate.

--
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sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
  #6  
Old May 7th 05, 01:28 PM
Ray Tomes
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Thanks to everyone for the many useful comments and references.

Joseph Lazio wrote:
No. Below a certain frequency, the waves cannot propagate. The
interstellar (and presumably intergalactic) medium has a plasma
frequency, given by 9 kHz*\sqrt{n_e} where n_e is the electron density
in units of cm^{-3}. In the local interstellar medium, n_e ~ 0.025
cm^{-3}, so waves with frequencies below 1 kHz just don't propagate.


What happens to an e/m wave below that cuttoff frequency?
The energy must go somewhere.

[[Mod. note -- If you have some source radiation below the cutoff
frequency, the light will be absorbed by the interstellar medium.
Think "light bulb outdoors on a foggy day". -- jt]]

--
Ray Tomes
http://ray.tomes.biz/
http://www.cyclesresearchinstitute.org/
  #7  
Old May 8th 05, 02:28 PM
Ray Tomes
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Ray Tomes wrote:
What happens to an e/m wave below that cuttoff frequency?
The energy must go somewhere.


And the moderator noted:
[[Mod. note -- If you have some source radiation below the cutoff
frequency, the light will be absorbed by the interstellar medium.
Think "light bulb outdoors on a foggy day". -- jt]]


Although the fog mainly scatters the light it cannot absorb it without
re-radiating at some other frequency. What I would like to know is the
equivalent thing for low frequency e/m waves between the galaxies? There
must be a resulting distribution of frequencies that the low frequencies
get converted to surely?

--
Ray Tomes
http://ray.tomes.biz/
http://www.cyclesresearchinstitute.org/
  #8  
Old May 8th 05, 03:02 PM
Paul F. Dietz
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Ray Tomes wrote:

Although the fog mainly scatters the light it cannot absorb it without
re-radiating at some other frequency. What I would like to know is the
equivalent thing for low frequency e/m waves between the galaxies? There
must be a resulting distribution of frequencies that the low frequencies
get converted to surely?


If EM radiation is below the plasma frequency, it doesn't propagate
at all, but is reflected. If the transmitter is embedded in a plasma
it doesn't radiate, or (if strong enough) blows a bubble in the plasma
due to radiation pressure. Some of the energy also gets dissipated
as heat due to the plasma's nonzero resistivity.

Paul
 




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