Why not just point the receiver at a star rather than having it scan 'empty' space?

Is there a reason that we are scaning all of the sky 'empty' or not?

I enjoy letting SETI use my processor time, just wanted to know.

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Why not just point the receiver at a star rather than having it scan 'empty' space?

Is there a reason that we are scaning all of the sky 'empty' or not?

I enjoy letting SETI use my processor time, just wanted to know.

S@H has no control over where the telescope points. We are piggybacking on searches being done by other groups/scientists that have scheduled telescope time.

When you're not paying for it, you take what you can get.

When you next look at the google sky image, gradually zoom in to an area of 'empty space' you see more and more distant objects between others, At the highest zoom setting, you can see the whole image background speckled with distant stars & galaxies. Now sure I don't expect to be able to receive a signal from that far, but the fact that the light itself gets here , however weak, indicates to me that a signal may come from just about any direction & distance. Picking places to look for signals would guarantee, by Murphy's Law, that you'll find one in the last place you look...[or of course never]

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"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.

Hi Tullameath,
Interesting choice of user names, i like it!

You could read this and it will explain how it works; The science of SETI@home

Or this; About SETI: Searching for Life

John.

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Related question: Arecibo is just a parabolic dish the size of a football field, right? How does anybody 'point' it? Isn't it merely being scanned through RA/Dec via the earth's motion?

Related question: Arecibo is just a parabolic dish the size of a football field, right? How does anybody 'point' it? Isn't it merely being scanned through RA/Dec via the earth's motion?

Nope.

It's a circular very big dish. (A section of a sphere.)

Clever things are done with the geometry of the secondaries to make it all work. Consequently, at any one instant the entire surface area is never used. A large 'spot' is viewed over a large proportion of the dish, angled to wherever in the heavens you wish to view.

Far easier to move the recievers carrage house than to move the dish!

The earth's rotation and orbit obviously add to the pointing equations.


Keep searchin',
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Is there an accessible technical reference about this?

A spherical dish would behave as a spherical lens, with a single focus albeit with considerable chromic aberation if my optics remember correctly.

A sphere has a constant radius of curvature and a single center. So that aperaturing a detector positioned at the focus (sphere's center) serves to direct the viewing but also reduce the sensitivity of the antenna, I would think.

Assuming the spherical section is more or less flat on the surface of the earth, then I would conclude that the signal to noise when viewing off (the geocentric) axis is lower than when looking directly on axis with the full NA of the antenna. If so, is there a sort of starmap available indicating the contours of equal S/N versus position in the cosmos (for a 'standard' receiver)? That would be interesting, too.

Is there an accessible technical reference about this?

Take a look on the Arecibo website?...

A spherical dish would behave as a spherical lens, with a single focus albeit with considerable chromic aberation if my optics remember correctly.

Yes. Hence the cleverness with the secondary 'optics'.

A sphere has a constant radius of curvature and a single center. So that aperaturing a detector positioned at the focus (sphere's center) serves to direct the viewing but also reduce the sensitivity of the antenna, I would think.

Yes indeed. However, that is a very small cost compared to the other far greater advantages for such a huge structure.

Also note that the primary funding for the structure was for ionosphere measurements. You only need to look straight up for that! The other star-gazing stuff was a useful bonus.

Assuming the spherical section is more or less flat on the surface of the earth, then I would conclude that the signal to noise when viewing off (the geocentric) axis is lower than when looking directly on axis with the full NA of the antenna. If so, is there a sort of starmap available indicating the contours of equal S/N versus position in the cosmos (for a 'standard' receiver)? That would be interesting, too.

Take a look on their website, or even ask them...


Good questions there,

Keep searchin',
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

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A spherical dish would behave as a spherical lens, with a single focus albeit with considerable chromic aberation if my optics remember correctly.

A sphere has a constant radius of curvature and a single center. So that aperaturing a detector positioned at the focus (sphere's center) serves to direct the viewing but also reduce the sensitivity of the antenna, I would think.

<<<<<


That might be true if one was examining the entire spectrum, but the band width compared to the entire spectrum is extremely narrow. Might be compared to an optical filter that just passes less than one percent of the total spectral width of visible light. Say just the sodium yellow, which actually two lines rather close together, rejecting all energy outside this frequency. Since the pickup antenna are movable to negate the rotation of the earth, one can remain on one spot in sky, or by not moving trace a line caused by rotation of the whole earth.


That the new receiving antenna collects seven times as much sky and polarization too means fourteen times the data compared to the original sampling. Free passage on the bus means no choice of destination, or more exactly the route taken.