What is the Universe expanding into..

Do you think there was anything before the big bang?

  • I don't think there was anything before the Big Bang

    Votes: 56 12.5%
  • I think something existed before the Big Bang

    Votes: 200 44.7%
  • I don't think the big bang happened

    Votes: 54 12.1%
  • I think the universe is part of a mutiverse

    Votes: 201 45.0%

  • Total voters
    447
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  • Star Collection.jpg
    Star Collection.jpg
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Yes, that was good, Galu. Made the point that a straight edge produces a diffraction spike at right angles.

And that the spikes depend on the shape of the aperture and any criss-crossing lines. This is calculated using something called the spatial fourier transform.

Eric Korpela explains it in detail:

https://www.quora.com/What-will-the...d-by-the-James-Webb-Space-Telescope-look-like

So the horizontal line in the image is produced by the top or vertical supporting strut of the JWST. The other two, surprisingly, overlap the hexagonal diffraction spikes.

S7 Diffraction Spikes JWST.jpg


This could have been avoided by the layout below.

System7 Space Telescope.jpg


I suppose that would have been harder to pack into a rocket.
 
I just need to look through the net curtains on my kitchen window to see the diffraction patterns around the distant street lamps.

The more distant lamps give the Hubble type spikes, while a closer lamp gives a striking horizontal interference pattern.
 
Evidently the threads of the net curtain form a geometric pattern, 🙂

Diffraction spikes are only a problem with bright objects, where the central star saturates the optics and you see thespikes.

James Webb is apparently reaching the limit of resolution known as diffraction limited. Exceeding lens imperfections.

Larger circular apertures give tighter resolution than small ones, as in this camera example:

S7 Diffraction limiting.jpg


Mathematically it is a Circular Sinc function or Airy Disk:

S7 Airy Disk aka Circular Sinc Function.jpg


This is related to the regular Sinc function which Fourier transforms to a square impulse or rectangular function. It even works with digital audio filters, but looks different with analogue filters which impart time delay to the impulse:

S7 Sinc and Rectangle Function under Fourier Transform.jpg


The Gaussian function that has a Fourier transform that is also a Gaussian. This avoids fringes. Lasers work like this.

S7 Circular Gaussian Function.jpg


Fascinating stuff. It's how it works.
 
...while a closer lamp gives a striking horizontal interference pattern.

Actually, the closer light source is a yellow, sodium-vapour street lamp.

The fact that the light it emits is nearly monochromatic explains the formation of the distinct interference pattern.

It looks similar to the middle image in the attachment.
 

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  • Interference Patterns.jpg
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I'm a bit surprised we don't have the tech to compensate/eliminate the diffraction digitally, revealing the real object.

Diffraction limits resolution, no matter how good the system is.

If two points on the object are closer to each other on the camera sensor than the pixel pitch, they will blend together no matter how small the pixel pitch is.

The finer detail of the object you would like to see, Pete, simply can not be resolved.
 
In photo terms that shot is blown meaning that the AC converter has produced all 1s. A star is a bright light source

Pete, TNT has already pointed out one limiting factor to seeing any detail in that star, and I have pointed out the other.

The star in the JWST image is just too bright and just too small.

Larger galaxies will image better.
 
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