Apollo moon hoaxers take a look at this:

Originally posted by googlefudge
ah, no the entire thing rings and all, is the diffraction pattern.

I think the rings are the diffraction pattern and the center disk is the theoretical best concentration of a light field for that size mirror. I bet there could even be a test of that idea: Suppose we make a square mirror, like just take a round mirror like we all see in scopes, and cut it square. I bet the airy disk would not be a perfect circle, the rings that is. I bet there would be some non-circularity in it, slightly out of round, approximately following the shape of the edge of the mirror. I wouldn't predict square airy rings but I bet they would not be totally circular either.

I wonder if there are pictures of the tests of the hex shaped mirrors going into the Webb space telescope that is the replacement for the Hubble? Would there be a tendency towards a hex shaped airy disk?

I think the theoretical end game of an infinitely large mirror, perfectly ground, would be a central peak with zero rings around it.

Originally posted by sonhouse
I think the rings are the diffraction pattern and the center disk is the theoretical best concentration of a light field for that size mirror.

If there was no diffraction, the central 'disc' would be a single point for most distant stars, and the resolution would be limited solely by the quality of the mirror and lenses, and the sensitivity of the sensor.

I bet the airy disk would not be a perfect circle, the rings that is.
That is correct. I have seen diffraction patterns for other shapes when I was looking up airy disks before, but cant seem to find an example right now.

I think the theoretical end game of an infinitely large mirror, perfectly ground, would be a central peak with zero rings around it.
The theoretical end game would be a perfect point for distant stars, and a perfect image complete with sunspots etc for nearer stars. The peak would not have the 'bell curve' shape that we currently get due to diffraction.

Originally posted by twhitehead
If there was no diffraction, the central 'disc' would be a single point for most distant stars, and the resolution would be limited solely by the quality of the mirror and lenses, and the sensitivity of the sensor.

[b]I bet the airy disk would not be a perfect circle, the rings that is.
That is correct. I have seen diffraction patterns for other s ...[text shortened]... rs. The peak would not have the 'bell curve' shape that we currently get due to diffraction.[/b]

An interesting experiment: An extremely large mirror, say the size of the sun, with a focal point say, 4.3 Ly away. If you aimed that mirror at Alpha Centauri for 5 years, the mirror if accurately aimed would put enough energy in the Alpha Centauri system to illuminate planets directly, scan the beam in a raster pattern across the system systematically, you would directly light up all the planets one by one! Of course you would be using a Hubble or something bigger to watch the display from Earth or somewhere in the solar system.

A mirror a million miles in diameter is a bit out of reach but since the same size mirror for a given frequency gives more resolution the lower the wavelength, then a mirror say 1 km across would give much more concentration of energy at optical wavelengths than radio wavelengths, so used as a kind of radar, Lidar, actually, it could do something like what I suggested.

Originally posted by sonhouse
An interesting experiment: An extremely large mirror, say the size of the sun, with a focal point say, 4.3 Ly away. If you aimed that mirror at Alpha Centauri for 5 years, the mirror if accurately aimed would put enough energy in the Alpha Centauri system to illuminate planets directly, scan the beam in a raster pattern across the system systematically, you ...[text shortened]... g a Hubble or something bigger to watch the display from Earth or somewhere in the solar system.

I am not sure why you would want to do that. All it would do would be to increase the brightness of objects. Surely it would be far more effective to use the same mirror as a telescope thus increasing the brightness of the image.

A mirror a million miles in diameter is a bit out of reach but since the same size mirror for a given frequency gives more resolution the lower the wavelength, then a mirror say 1 km across would give much more concentration of energy at optical wavelengths than radio wavelengths, so used as a kind of radar, Lidar, actually, it could do something like what I suggested.
I don't quite understand all that. Are you saying a 1km mirror could shine a spot on an Alpha Centauri planet bright enough for us to see?

Originally posted by twhitehead
I am not sure why you would want to do that. All it would do would be to increase the brightness of objects. Surely it would be far more effective to use the same mirror as a telescope thus increasing the brightness of the image.

[b]A mirror a million miles in diameter is a bit out of reach but since the same size mirror for a given frequency gives mo ...[text shortened]... saying a 1km mirror could shine a spot on an Alpha Centauri planet bright enough for us to see?

The Hubble, at 2 meters, can parse a circle into 25 million parts. If it was 2000 meters, it could parse the circle into 25 billion parts. That is one way, a useful way, of looking at telescope resolution. So draw a circle with the radius of 4.3 light years and you end up with a circumference of 1.4 E14 miles. Divide that by 25 billion and you have a resolution of 6200 miles so a properly aimed mirror could in fact put a 6000 mile wide dot of light on a planet (assuming you found one and aimed it with the incredible accuracy to actually hit that planet) in orbit around any one of the three stars in the Alpha Centuari system.

Of course you would not have to actually shine a light like that, you would be able to have enough resolution to be able to resolve it as a disk and then do spectrographic studies to determine if it had an atmosphere, what kind, the temperature, is there water, that kind of thing.

A 20 km mirror would therefore have a resolution of about 600 miles at that distance. That would give you a lot more information.

A 200 Km mirror would give 60 mile res, etc.

The thing is, for resolution purposes, it doesn't have to be an actual 200 km mirror.

Modern technology can combine the light data from separated mirrors in the optical world just like radio astronomers right now combine data from radio telescopes all around the planet and they are right now getting radio resolution as if the reflectors were the size of the entire Earth.

In the optical world, we are taking it a step at a time, now with mirrors several hundred feet apart but scopes in space with the optical data linked by lasers could be thousands of kilometers apart, of course in the future, maybe 30 years from now, but doable, so they simulate a mirror for resolution purposes, not total light gathering power of course, of a mirror the size of the distance between them.

So two mirrors linked in space by lasers, separated by 2 million km could theoretically give a resolution of about 10 METERS at Alpha Centauri.

So that same system could give 100 meter res at 40 light years out or 1 km at 400 light years, 10 Km at 4000 light years, enough to spot billions of planets and to see exactly what kind of atmosphere, is there liquid water, the temperature, even if there were cities generating lights like ours would appear if we spotted Earth from 4000 light years away with that same telescope system.

That kind of resolution of course is in the future but once the technology is in place to do it at 1 km, 10 km would follow, 100 km after that,etc.

Originally posted by sonhouse
That kind of resolution of course is in the future but once the technology is in place to do it at 1 km, 10 km would follow, 100 km after that,etc.

Actually, once the technology is in place, we would probably start with as large as possible. We would probably however start with earth orbit satellites with a direct line of sight to each other that doesn't go through too much atmosphere. So I don't think it would go 1km, 10km, .... but rather depend on the placement of the satellites.

Originally posted by twhitehead
Actually, once the technology is in place, we would probably start with as large as possible. We would probably however start with earth orbit satellites with a direct line of sight to each other that doesn't go through too much atmosphere. So I don't think it would go 1km, 10km, .... but rather depend on the placement of the satellites.

You are thinking in terms of satellites around Earth. I am thinking in terms of probes in space far from Earth, the farther the better. For instance, there is a dust cloud around the distance of Neptune I think called Gigenshien, something like that, don't pretend to know the proper spelling, but anyway, ALL telescopes in and around Earth, Hubble, Webb, whatever, are limited by that cloud. If you can get a system of telescopes past Neptune, maybe out to pluto and separated by a few million Km, the full use can be made of the technology, if the same equipment were say, only 100 million Km away from Earth it wouldn't do any better than if it was around Jupiter. Only if you get past Neptune can optics be used down to its own limit.

That is one limitation of very large telescopes near Earth that cannot be overcome no matter what kind of super technology you implement. It clouds the images of stars trying to get images of planets and so forth because the star lights up the cloud and that light, dim as it is, for the best of the best, interferes with imaging objects close to a star.

That said, you can still do a lot of great science if you can get them separated by any distance.

The problem with just jumping to the greatest distance is you have to start small, that's why the multiple mirror scopes on earth are not very far apart, they have to have vacuum tunnels between them, accurate laser beams and so forth. It's a very tricky technology, a lot harder to accomplish than the combinations of radio telescopes that has been going on for 50 years or more. The latest on that front is a Russian craft with an onboard radio telescope has just been launched with the idea of putting it in a way looping orbit that actually goes past the moon and connected to the system of telescopes on earth to extend the effective size to the distance between them so instead of an effective reflector size of 8000 miles or 13000 Km, it would be 300,000 miles or about 500,000 km, expanding the resolution of radio telescopes 40 times what is available to earth bound systems of radio telescopes now. Mind you, there would be little if any increase in the sensitivity of the scope but the resolution will be phenomenal. The radio telescope system is already hundreds of times greater resolution wise than even the Hubble because of the vast overall effective size of the reflectors. They talk about milli and micro arc seconds of resolution where the Hubble can only do about 0.05 arc seconds, phenomenal enough but come back in 50 years...

The problem with radio telescopes is resolution is related to not only just the mirror size but the wavelength as well, so if you build a radio telescope for 1 Ghz, a wavelength of about 1/3 meter and you get X amount of resolution, if you want to use it at 0.5 Ghz, the same dish will now have half the resolution because the wavelength is now about 2/3 meter in size.

So if you go the other way in frequency, 10 Ghz, that same dish now has 10X the resolution of the 1 Ghz frequency because there are ten wavelengths at 10 Ghz for every one wavelength at 1 Ghz.

If you used a radio telescope with a 2 meter dish and you were observing at 2 meters, you would only be able to concentrate one wave at a time so would not get much gain in sensitivity or resolution. But a 2 meter dish at 0.002 meters would now have not one thousand wavelengths but 1000X1000 wavelengths, times .78 if it was a circular shaped dish, or 780,000 waves concentrated to one so you can see as you go up in frequency, or down in wavelength, the same mirror gives you greater resolution.

So a two meter mirror like the Hubble can give that 0.05 arc second resolution but if it was a radio telescope at 1 meter wavelength it could only concentrate about 3 waves into one with a very poor angular resolution, maybe 30 degress or so at best, a far cry from .05 arc seconds.

That's why they need separation of dishes as far apart as possible to surpass the resolution of the Hubble, which now, they do with ease. They can see stuff that the Hubble can't because it is at Ghz frequencies and with much much better resolution than the Hubble could ever think about.

So if you can make two Hubble's separated by a few thousand Km in space, communicating phase data by laser beam, the resolution would far exceed the best radio telescopes.

But for the absolute best use, they need to be out in space past Neptune to avoid the fogging due to the Gegenschein, ( I googled it):

http://en.wikipedia.org/wiki/Gegenschein

It's only an issue if your looking at stuff in the ecliptic.

Which is what you would expect as the solar system formed from a spinning disk.

Also I would point out that to resolve planets from their stars you don't need a resolution high enough to have them exactly occupy one pixel...
You just need to be able to resolve separate points of light from the star and an object the distance of the planets orbit away from the star.

Which is how people have already resolved extrasolar planets.

Originally posted by googlefudge
It's only an issue if your looking at stuff in the ecliptic.

Which is what you would expect as the solar system formed from a spinning disk.

Also I would point out that to resolve planets from their stars you don't need a resolution high enough to have them exactly occupy one pixel...
You just need to be able to resolve separate points of light fr ...[text shortened]... ets orbit away from the star.

Which is how people have already resolved extrasolar planets.

Yeah, I saw the ecliptic thing. You can glean some information from these single pixel images but those planets were a lot bigger than Earth which is what we are really interested in, not super jupiters one kg away from being a red dwarf. I think there will be telescopes of the power I spoke, obviously each generation of scopes will exceed the last and eventually they will have the kind of res that will be able to spot city lights if such exists, which is very unlikely. The latest news says we should look for planets around stars heavy in metals (anything heavier than lithium is a metal to astronomers) And I would think a place to look would be the stars that formed at the same time as Sol, astronomers have tracked where they are now, in a rough line about 5000 light years long, there was an article in Scientific American about them. Since they were formed from the same cloud that formed the solar system, my guess is that loose cluster would have the same kind of stars and conditions that led to Earth. It would take an incredible scope to see planets there though, I think that may come about in the 22nd century however. Like I said, if you can combine the phase of two scopes 2 million Km away, you can get individual planet wide res at 4000 light years and if it can be done and our civilization doesn't crash in the next couple hundred years, it will be done.

Originally posted by sonhouse
Yeah, I saw the ecliptic thing. You can glean some information from these single pixel images but those planets were a lot bigger than Earth which is what we are really interested in, not super jupiters one kg away from being a red dwarf. I think there will be telescopes of the power I spoke, obviously each generation of scopes will exceed the last and even ...[text shortened]... n be done and our civilization doesn't crash in the next couple hundred years, it will be done.

Unless you are trying to image the planets surface. Which requires a vast telescope.

All planets will be points of light.

The trick to spotting them is to have a resolution high enough that you can separate the points of light from the star. which requires the angle of arc per pixel to be less than the planets orbital radius.

(plus some tricks to eliminate the glare from the star)

Originally posted by googlefudge
Unless you are trying to image the planets surface. Which requires a vast telescope.

All planets will be points of light.

The trick to spotting them is to have a resolution high enough that you can separate the points of light from the star. which requires the angle of arc per pixel to be less than the planets orbital radius.

(plus some tricks to eliminate the glare from the star)

It won't require a 'vast' telescope if aperture synthesis technology in space is fully developed, where they can separate the scopes by a million Km or so. Two Hubble's with aperture synthesis would do the job nicely.

Originally posted by sonhouse
http://www.youtube.com/watch?v=EBM854BTGL0&feature=relatedwww.physorg.com/news/2011-09-lroc-images-sharper-views-apollo.html

The tracks left by the explorers are shown in these new photos.

How do you hoax theorists explain these new photos?

Why that is simple. Aliens put the tracks there.

Next?

Originally posted by sonhouse
It won't require a 'vast' telescope if aperture synthesis technology in space is fully developed, where they can separate the scopes by a million Km or so. Two Hubble's with aperture synthesis would do the job nicely.

With an unbelievably long exposure time ;-)

I was talking about distributed interferometers not solid scopes, should have made that clear, sorry.

Originally posted by whodey
Why that is simple. Aliens put the tracks there.

Next?

Ahh, I think you got lost,
The spiritually forums are two doors up.

Originally posted by googlefudge
With an unbelievably long exposure time ;-)

I was talking about distributed interferometers not solid scopes, should have made that clear, sorry.

I think you still need mirrors to concentrate enough light to go to an interferometer so the two go together. At least that is my take on it.