Will E@H find many more pulsars?

Mike Hewson
Mike Hewson
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Late 1940's actually. One

Late 1940's actually. One really clever idea was a crude form of interferometry whereby setting up a simple Yagi aerial type receiver on an eastward & ocean facing clifftop ( near Sydney ) demonstrated and helped to localise sky sources. No pulsars were found ( that came in the 1960's ) but broader sources like interstellar gas clouds or large supernovae remnants ( eg Crab nebula ) could be picked up by interfering a direct line-of-sight signal with the same but bounced off the ocean at low angles. The water's surface acted like a mirror at the relevant wavelength of around 1.5m so a spot of geometry could reveal ( to within some appreciable error ) where on the sky the object was. Thus a sinusoidal pattern at the receiver as the Earth rotated during the rise of some Eastern sky source were also correlated with those on a Western & ocean facing clifftop in New Zealand as those same sources were setting.

Significantly many such radio sources did not correspond to anything known to visual astronomy and some clearly radiated at powers well beyond that measured for visual wavelengths. In fact measurements at certain radio wavelengths yielded an effective temperature of the Sun well over one million degrees, and emphatically not the expected 6000 or so! This was the corona of course, and to this date we still don't have a clear answer to why it is that hot. It took a little while for the general astronomical community to swallow the import of these findings, but once so then, well, the rest is history : including all the complicated dishes & things used now which are far superior .......

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

telegd
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Mike, thanks for your

Mike, thanks for your thoughtful and detailed answer. I was aware of some of the E@H history, but it is always nice to have more detail.

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As I'll be in Hannover next week for the public event, I've just put your query on my 'to-do/inquire list'. :-) :-)


Much appreciated!

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Note that I think the beams we're doing are in the anti-galactic-centre direction ( looking out of the galaxy as opposed to inwards ) so that's naturally rather more sparse...


That is certainly the explanation that I had heard. However, the graphics at the bottom of the page you linked are squarely centred on 0,0. Unless I am reading it incorrectly, that would be the galactic core, no?

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Although we have a natural urge to delight if we find something new, it doesn't mean that our time & effort is wasted if not. Far from it. Many surveys like this can put upper bounds on population statistics for objects of 'type X'.

I certainly appreciate this - I know that no serious observational effort in science is ever wasted. I just thought it would be interesting to know what our scientists had predicted that we should see. As you say, it is just as interesting if you don't get what you expect.

telegd
telegd
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RE: One really clever idea

Quote:
One really clever idea was a crude form of interferometry whereby setting up a simple Yagi aerial type receiver on an eastward & ocean facing clifftop ( near Sydney ) demonstrated and helped to localise sky sources.

If my life wasn't so full already, I thought it would be fun to try to build an amateur radio telescope that would detect one of the louder pulsars. My Ham skills have rusted into nothingness, so it is mostly fantasy. Interestingly, just searching now shows that it is an active field:

http://www.radio-astronomy.org/node/174

I will stick to trying to learn Semi-Riemannian Geometry instead...

tolafoph
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RE: RE: One really clever

Quote:
Quote:
One really clever idea was a crude form of interferometry whereby setting up a simple Yagi aerial type receiver on an eastward & ocean facing clifftop ( near Sydney ) demonstrated and helped to localise sky sources.

If my life wasn't so full already, I thought it would be fun to try to build an amateur radio telescope that would detect one of the louder pulsars. My Ham skills have rusted into nothingness, so it is mostly fantasy. Interestingly, just searching now shows that it is an active field:

http://www.radio-astronomy.org/node/174

I will stick to trying to learn Semi-Riemannian Geometry instead...

I made your link clickable.

Mike Hewson
Mike Hewson
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RE: Mike, thanks for your

Quote:
Mike, thanks for your thoughtful and detailed answer. I was aware of some of the E@H history, but it is always nice to have more detail.


You're welcome!

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That is certainly the explanation that I had heard. However, the graphics at the bottom of the page you linked are squarely centred on 0,0. Unless I am reading it incorrectly, that would be the galactic core, no?


Yup, basically in Sagittarius.

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I certainly appreciate this - I know that no serious observational effort in science is ever wasted. I just thought it would be interesting to know what our scientists had predicted that we should see. As you say, it is just as interesting if you don't get what you expect.


Well, who can say? Maybe there's some quieter/weirdo dark matter material that you'd only hear in the anti-galactic direction - cos there's too much background to sort through towards the core - by use of careful signal analysis. William Herschel was the inventor of the sky survey : sit and watch and record what you see ..... if you find something to patternise then so much the better.

Quote:

If my life wasn't so full already, I thought it would be fun to try to build an amateur radio telescope that would detect one of the louder pulsars. My Ham skills have rusted into nothingness, so it is mostly fantasy. Interestingly, just searching now shows that it is an active field:

http://www.radio-astronomy.org/node/174


The post WWII guys used gun-laying radar units - classic valve stuff - so the circuitry behind your 'dish' is the easy part with modern solid state. It'll be getting a good size beam bucket and steering ( ie phases ) that'd be the challenge. Oh and every body forgets to mention the ground plane : you need a good one of those.

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I will stick to trying to learn Semi-Riemannian Geometry instead...


The trick is to understand differentials ( 'one-forms' ) which act like tiny little arrows at some point, such arrows are bundled together as an ultra-local co-ordinate system, and you get a new set for every point in your space/manifold. When you traverse some space these differentials are one's stepwise guide. As Riemann showed you can deduce the topological nature of the space you're in without gaining an 'exterior' view, essentially by keeping track of the differentials. The underlying assumption is that any ( smooth ) manifold's geometry is locally flat provided you just zoom in close enough.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

telegd
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I was obviously just a little

I was obviously just a little too impatient for new results!

http://einsteinathome.org/node/195850
http://einsteinathome.org/node/195858

Martin Ryba
Martin Ryba
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RE: One really clever idea

Quote:
One really clever idea was a crude form of interferometry whereby setting up a simple Yagi aerial type receiver on an eastward & ocean facing clifftop ( near Sydney ) demonstrated and helped to localise sky sources. No pulsars were found ( that came in the 1960's ) but broader sources like interstellar gas clouds or large supernovae remnants ( eg Crab nebula ) could be picked up by interfering a direct line-of-sight signal with the same but bounced off the ocean at low angles. The water's surface acted like a mirror at the relevant wavelength of around 1.5m so a spot of geometry could reveal ( to within some appreciable error ) where on the sky the object was.

In another thread, there was the recent announcement of the Russian HEO radio astronomy satellite that will give some really good interferometry. Another interesting type of (cruder) long baseline interferometry is "moon bounce." I don't know if they ever got it to really work well, but when I was at Arecibo a friend was experimenting with it. Point the (low gain) Yagi antenna directly at the source (e.g., Jupiter) and the high gain (Arecibo) at the Moon to see if you can pick up correlated signals.

Experimental astronomers are exceedingly resourceful beasts.
-Marty

"Better is the enemy of the good." - Voltaire (should be memorized by every requirements lead)

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