Well of course you can, you're a Fantasist on another planet.
How fast does gravity travel???
- Thread starter Dork Lard
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Well of course you can, you're a Fantasist on another planet.
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I apologise, in that massive image I wasn't sure of what you were looking at! and astigmatism to some, manifests as a 'lens flare' effect.
I'm afraid, I'm still not exactly sure of what you are seeing (astrophotography isn't my forte!), but there is a heck of a lot of gravitational lensing in that image!
And another question I don't know the answer to - as this image is such a deep field, apart from light that has been lensed, would there be much light from behind the focus plane?
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I apologise, in that massive image I wasn't sure of what you were looking at! and astigmatism to some, manifests as a 'lens flare' effect.
I'm afraid, I'm still not exactly sure of what you are seeing (astrophotography isn't my forte!), but there is a heck of a lot of gravitational lensing in that image!
And another question I don't know the answer to - as this image is such a deep field, apart from light that has been lensed, would there be much light from behind the focus plane?
This helps: There's an explanation here https://www.livescience.com/james-webb-telescope-deep-field-explained
which answers most of it.
Deep field appears to mean covering a range of distances, but as far as I've seen so far, in astronomy, DOF isn't an issue. Yes light from any distance would make it to the telescope. I'd have expected more of those teeny weeny little dots - presumably far distant - to be redshifted.
Intresting facts:
| Focal length | 131.4 m (431 ft) |
|---|---|
| Focal ratio | f/20.2 |
It does NOT come in a Nikon E mount, and
it can only see wavelengths from 600nm up, so no yellow green or blue. It won't see the little men on Mars, then
Obviously they're green.I probably relates to the instrument used, imaging rather than pure spectrographic modes. Astro telescopes are optically correct for images at infinity to some accuracy so depth of field is a bit of a misnomer. It may need to a touch of focus changing from say a solar object to a star but galaxial distances are so enormous that the error from true infinity which is a mathematical concept that sets the shape are so small that it doesn't matter, I'd guess that each of the separate mirrors that make up the large one are independently adjustable so that they can be light weight. Ground based mirrors need to be massive or have similar adjustments of some sort to account for gravity effects. A 250mm mirror i made would need to be 50mm thick to retain it's shape to ~1/10 wave of light orientated at various angles.
It seems it covers
Webb will be a 6.5m telescope sensitive from gold-colored visible light to the mid-infrared, at wavelengths ranging from 0.6 micrometers to 28.5 micrometers.
The wavelength viewed also sets the max resolution that can be achieved.
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"Deep field" I've found referring to a few different things, from "a very long exposure so you can see a long way" to various combinations of several images.
"That" DF image is described
This deep field, taken by Webb’s Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope’s deepest fields, which took weeks.
Those 18 mirrors on the Webb are of 3 different designs, and each adjustable for focus, and 7 degrees of freedom. Something of an advantage after the Hubble cock-up. They refocus it every few days.
This 'scope is stuffed full of techy details.
There's a Mercury BepiColumbo project ongoing, coming up is JUICE Jupiter mission, Mars gets Franklin, three's an asteroid probe - and a planned next telescope astro to be launched around 2040. I'll be 39 then.
"That" DF image is described
This deep field, taken by Webb’s Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope’s deepest fields, which took weeks.
Those 18 mirrors on the Webb are of 3 different designs, and each adjustable for focus, and 7 degrees of freedom. Something of an advantage after the Hubble cock-up. They refocus it every few days.
This 'scope is stuffed full of techy details.
There's a Mercury BepiColumbo project ongoing, coming up is JUICE Jupiter mission, Mars gets Franklin, three's an asteroid probe - and a planned next telescope astro to be launched around 2040. I'll be 39 then.
I would point out that we can actually resolve images of galaxies that are 32 billion light years away and we can detect light that is 41 billion years away and all this when we live in a universe that is only 13.8 billion years old. The reason is fairly straight forward, space/time is not a flat thing, its a lumpy soup punched through by gravity. We can view directly the universe as it was 13.1 billion years ago. The whole of the universe upto 13.1 billion years ago is visible. Space/time has not expanded at a constant rate, it expands and contracts, the visibility today of an object on the far side of the universe is dependant of the path the energy has taken to get here, through a dense area of space time will slow and the light will bunch up according to our viewpoint, space/time stretched out wow it appears that light arrives faster, but as einstein pointed out that's all relative to the position of the observer.
The field of view will be miniscule probably a few arc seconds. It will be mentioned in the specs - somewhere. The scope is a Cassegrain design but additional optics are usually added to improve the field of view which gets smaller and smaller as size goes up. Astro photo's often map detected colour/wavelength to some suitable visual colour. Additional detail can sometimes be found by looking at specific narrow wavelength bands of light.
Hubble according to early reports from the horses mouth. There is a wiki page on Foucault testing best read it rather than try and explain here. The test is a null test for a perfect sphere. The mirror darkens all over rather than in zones as the knife edge is moved. A British optician called Dall came up with an idea to make a parabola behave in the same way. It just needed a simple lens placed in the light beam. Hubble would need one or more to achieve accuracy on such a large mirror. The lens system has to be spaced a specific distance from the light source and they got that wrong and didn't use a 2nd method of checking. The straight ordinary Foucault with a mask on the mirror might have shown the error but it's not that easy a test to do especially with shorter and shorter focal length mirrors but variations on it probably would have shown the error - caustic test for instance.
en.wikipedia.org
Hubble according to early reports from the horses mouth. There is a wiki page on Foucault testing best read it rather than try and explain here. The test is a null test for a perfect sphere. The mirror darkens all over rather than in zones as the knife edge is moved. A British optician called Dall came up with an idea to make a parabola behave in the same way. It just needed a simple lens placed in the light beam. Hubble would need one or more to achieve accuracy on such a large mirror. The lens system has to be spaced a specific distance from the light source and they got that wrong and didn't use a 2nd method of checking. The straight ordinary Foucault with a mask on the mirror might have shown the error but it's not that easy a test to do especially with shorter and shorter focal length mirrors but variations on it probably would have shown the error - caustic test for instance.
Foucault knife-edge test - Wikipedia
en.wikipedia.org
Infinity of stars; As Carl Sagan said; there are billions of billions of galaxies that each have billions of billions of stars. Or summat like that. The problem is that stars disappear and new stars are born, constantly, which makes it impossible to count. (amongst the other reasons why counting is impossible?) You could perhaps say there are x number of stars at any one millisecond in time. But, ask a couple thousand experts and you'll get a couple thousand answers, all of which would be estimates. So it kind of makes the number of stars seem infinite, even though it clearly isn't. I also think previous posts crossed over between infinite number of stars and infinite distance, which doesn't help with clarity. Hope that's cleared things up though.
It's safer to say that a number of factors do not stack up as expected and no one knows why. The early signs caused the terms dark matter and energy to appear to try and make them stack up on the basis that they must be there. It's a general aspect of astrophysics. Things are assumed from what we can actually measure. Red shift is determined by emission spectra as explained here
Red-shift - The expanding Universe - AQA - GCSE Physics (Single Science) Revision - AQA - BBC Bitesize
Learn about and revise red-shift, the expanding Universe, the Big Bang theory and the future of the universe with GCSE Bitesize Physics.
www.bbc.co.uk
This area and detecting variations and doppler shifts in light from stars also figures in detecting planets. According to sone news people might think they are actually be resolved.
Other ways of measuring distance. One is angular variation based on the baseline of the earths orbit around the sun. This allowed Cephied variable stars to be studied. From that any star anywhere of that type is treated as a Cepheid variable so it's distance can be determined purely from light levels. Then red shift. It's all based on theories and we can't go and look or get a tape measure out.
It's not as simple as that due to red shift. Extend that far enough and we have no way of detecting it. Anyway distance is detected by movements of absorption lines as the BBC article explains. The max wave length is set by the stuff that is examining it. The other aspect of IR is that it passes through "stuff" without being messed up as much as visible light.
My use of the word infinity related to the shape of a telescope mirror, It's a mathematical fact and the distances involved in use means no significant difference to infinity. Resolution is set by the diameter of the mirror and also importantly the wavelength being studied. A mirror for visible light needs to be made more accurately than one for IR. One metric is 1/4 of the wavelength being studied which is close to the theoretical limit but they may chose to go further. For people feeling a bit manic if interested
From memory Hubble was figured to the wrong shape to 1/30 wave. Why - no atmosphere as that disrupts light and limits resolution as well. Large ground based telescopes are sometimes fitted with some interesting gear to improve that aspect - variations in it as photo's are taken.
In the early days some observers using these made use of the hands, feet and mouth to achieve the same thing.
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All sorts of holes in some of the above... I'll only pick up that Hubble's mirror error was about 60 times what was stated - they checked it against the thing they made it with - oops.
That's similar to a problem with diy-ground mirrors, they can be smooth to some fraction of λ but "miles" out of sphericity.
On the JWT, nice images with explanations here.
That's similar to a problem with diy-ground mirrors, they can be smooth to some fraction of λ but "miles" out of sphericity.
On the JWT, nice images with explanations here.
They figured it to the accuracy they wanted according to the gizmo used - the problem was an error in producing the gizmo. An incorrectly sized or installed spacer. My recollection is that sizing was the problem. Confusion when the design was moved to actual manufacture. They corrected Hubble eventually by adding something similar to a schmidt camera corrector plate but designed for that specific job.
It worked because the main mirror was incredibly accurately out which allowed them to design it to suite.A parabola is nothing remotely like a sphere and with shorter and shorter focal lengths and increasing diameters the differences get even larger.
There are also various designs of cassegrain type telescopes that use curvatures other than parabolic. This one for instance
Ritchey–Chrétien telescope - Wikipedia
The Web is actually a 4 mirror off axis system. All mirror means no chromatic aberration problems. One it seems is flat.
The paper on that page gives more explanations,
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It would be better if you googled for yourself and asked when you find something you don't understand.
Tell us what you understand by the term "the speed of gravity"?
One answer to your question is that the instrument may help test theories which form an overall picture.
The impression you're giving, from your abusive responses, is that you have little science education, no respect for those who have more, so try to be a complete jerk because you're embarrassed. If that's not the case, stop trying to take the píss out of things you're clueless about and the people who try to help. OK?
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