JWST images

[Macavity]

The redoubtable Maggie Aderin-Pocock on the "One Show"... 
"Blowing the minds" of the presenters (P'raps not too hard)! 🥳

Anyways... BBC2 (England) Tomorrow (Thu) 8 p.m to 9 p.m.
"Super Telescope: Mission to the Edge of the Universe" 😎
https://www.bbc.co.uk/programmes/m00197px

Edited July 13, 2022 by Macavity

[The Lazy Astronomer]

2 hours ago, gorann said:

I have not followed all the entries on this thread, so maybe this has been discussed: JWST is an IR telescope and I got quirious. Has anyone here tried IR astrophotogtaphy? Googling it gives rather few entries, but this one got me interested:

https://www.cloudynights.com/topic/554666-nirha-preview-of-horsehead-project/

My instinctive reaction is it probably wouldn't be worth the time required just for a pretty picture (if it would even turn out that pretty anyway). We would probably need somebody with a larger aperture, dual rig setup, who has a penchant for undertaking different and interesting imaging challenges. Now, if only there was someone like that around here... 🤔

[Padraic M]

2 hours ago, gorann said:

I have not followed all the entries on this thread, so maybe this has been discussed: JWST is an IR telescope and I got quirious. Has anyone here tried IR astrophotogtaphy? Googling it gives rather few entries, but this one got me interested:

https://www.cloudynights.com/topic/554666-nirha-preview-of-horsehead-project/

This chap has experimented with an IR-pass filter and a mono sensor to capture galaxies from Tokyo centre with reasonable results. It's on my list of things to try as part of a narrowband setup in Bortle 8 at some stage.

https://satakagi.github.io/IR-imaging-of-galaxies-under-light-pollution/

http://uwakinabokura.livedoor.blog/archives/9101874.html

Edited July 13, 2022 by Padraic M

[wimvb]

3 hours ago, gorann said:

I have not followed all the entries on this thread, so maybe this has been discussed: JWST is an IR telescope and I got quirious. Has anyone here tried IR astrophotogtaphy? Googling it gives rather few entries, but this one got me interested:

https://www.cloudynights.com/topic/554666-nirha-preview-of-horsehead-project/

Near infrared would be doable. There are a few things to consider:

1. The transmittance of glass in your telescope. Glass can block IR. From 2.5-3 um glass can be opaque. In IR cameras, germanium is used as a lens material. A reflector doesn’t have this problem. Also, chromatic aberration can be a serious problem since refractors aren’t designed for IR wavelengths. All in all, a reflector is a safer bet.

2. Reflectance of mirror coating. For wavelengths longer than 500 nm (green), gold has higher reflectance than aluminium. As we all know, gold doesn’t reflect blue light. But it does reflect IR very well.

3. Camera needs to be sensitive to IR. Longer wavelength IR is heat radiation. You need to cool the camera a lot. The camera shouldn’t have IR blocking glass, of course. This is the main problem. IR sensitivity if silicon cmos is poor. One could try persuading ZWO to make a camera  with a FLIR sensor.

4. The atmosphere blocks some IR wavelengths. IR light up to 5 um wavelength is ok.

All in all, NIR astrophotography up to 1 um is doable, but longer wavelengths will be a challenge.

[wimvb]

(double post)

Edited July 14, 2022 by wimvb

[badhex]

As other have mentioned, I haven't followed every single post so maybe this has been discussed, but I have a question:

So, in a conventional telescope we can correct for many aberrations created by the optical elements, e.g. CA by using multiple objective elements or Coma with a Paracorr etc. If, like the JWST we are using a large gravitational body such as a galaxy cluster as one of the optical elements in our train, clearly we cannot create a physical corrector as this would need to be different for each different gravitational body we use.

That said, if we know the data representing the physical properties of the gravitational bodies we are using as an optical element, then surely a model can built using that data to then transform the images digitally, after the fact, and restore some of the shapes and positions of the smeared galaxies we see in the JWST images? Like a sort of digital Paracorr or field flattener, let's say? 

Obviously, such a transformation could not restore data that was not captured, much like there are limits to taking a small low res image and trying to make it larger - the information simply was not recorded in the original image, but perhaps we could grt some of the way there? 

Maybe this is nonsense, but would love to hear from people with a better understanding of the physics than I. 

[Alien 13]

16 minutes ago, badhex said:

As other have mentioned, I haven't followed every single post so maybe this has been discussed, but I have a question:

So, in a conventional telescope we can correct for many aberrations created by the optical elements, e.g. CA by using multiple objective elements or Coma with a Paracorr etc. If, like the JWST we are using a large gravitational body such as a galaxy cluster as one of the optical elements in our train, clearly we cannot create a physical corrector as this would need to be different for each different gravitational body we use.

That said, if we know the data representing the physical properties of the gravitational bodies we are using as an optical element, then surely a model can built using that data to then transform the images digitally, after the fact, and restore some of the shapes and positions of the smeared galaxies we see in the JWST images? Like a sort of digital Paracorr or field flattener, let's say? 

Obviously, such a transformation could not restore data that was not captured, much like there are limits to taking a small low res image and trying to make it larger - the information simply was not recorded in the original image, but perhaps we could grt some of the way there? 

Maybe this is nonsense, but would love to hear from people with a better understanding of the physics than I. 

I am sure this would be possible the same way a DSLR can have "lens data" to correct any pin cushioning etc or even to de-fish a fisheye lens.

Alan

[wimvb]

10 minutes ago, badhex said:

As other have mentioned, I haven't followed every single post so maybe this has been discussed, but I have a question:

So, in a conventional telescope we can correct for many aberrations created by the optical elements, e.g. CA by using multiple objective elements or Coma with a Paracorr etc. If, like the JWST we are using a large gravitational body such as a galaxy cluster as one of the optical elements in our train, clearly we cannot create a physical corrector as this would need to be different for each different gravitational body we use.

That said, if we know the data representing the physical properties of the gravitational bodies we are using as an optical element, then surely a model can built using that data to then transform the images digitally, after the fact, and restore some of the shapes and positions of the smeared galaxies we see in the JWST images? Like a sort of digital Paracorr or field flattener, let's say? 

Obviously, such a transformation could not restore data that was not captured, much like there are limits to taking a small low res image and trying to make it larger - the information simply was not recorded in the original image, but perhaps we could grt some of the way there? 

Maybe this is nonsense, but would love to hear from people with a better understanding of the physics than I. 

In order to do that, you would need to know the exact mass distribution in the lensing galaxies, and the exact position of tbe lensed galaxies. You could actually change the problem; figure ot the distribution of matter in the lensing galaxy, assuming that the lensed galaxy is an ordinary spiral. This could then be used to study the foreground galaxies. It's similar to determining the mass of say, Jupiter by studying the orbits of its moons. With lensing galaxies, you would probably need to do simulations, but it could tell a lot about the mass distribution and black holes in those galaxies. Studying only one such scenario wouldn't give much. But if you do this for several gravitational lenses, you'd build a knowledge base that would allow further refinements. I have no idea if scientists are already doing this.

[wimvb]

1 minute ago, Alien 13 said:

I am sure this would be possible the same way a DSLR can have "lens data" to correct any pin cushioning etc or even to de-fish a fisheye lens.

Alan

A dslr lens is much simpler, because a well known test pattern is used to determine the lenses characteristics, so the lens is well known. In the case of gravitational lenses, the lens is unknown. It's like looking at a landscape image and trying to determine both what aberrations the lens has, and what the landscape really should look like.

[saac]

Re gravitational lensing and reconstruction of image - https://skyandtelescope.org/astronomy-news/incredible-resolution-reconstructed-galaxy-pushes-hubbles-limits/

 

Jim 

[markse68]

What type of galaxy are these foreground ones? They are incredibly bright and blob shaped 

Mark

[markse68]

8 hours ago, wimvb said:

1. The transmittance of glass in your telescope. Glass can block IR. From 2.5-3 um glass can be opaque. In IR cameras, germanium is used as a lens material. A reflector doesn’t have this problem. Also, chromatic aberration can be a serious problem since refractors aren’t designed for IR wavelengths. All in all, a

I guess the filters are made from Germanium then? I thought the transmission values looked a bit low

Mark

[wimvb]

49 minutes ago, markse68 said:

I guess the filters are made from Germanium then? I thought the transmission values looked a bit low

Mark

Nope, the lenses themselves are made from this semiconductor. Germanium has about 50% transparency for wavelengths longer than 2 um. As a bit of trivia, germanium is also valued as a material to make amplifier transistors in particularly electric guitar amplifiers. According to a guitar playing former colleague.

[wimvb]

1 hour ago, markse68 said:

What type of galaxy are these foreground ones? They are incredibly bright and blob shaped 

Mark

Most likely elliptical. M87, which hosts the black hole that was imaged by the Event Horizon Telescope, is a nearby example of this type of galaxy.

Edited July 14, 2022 by wimvb

[markse68]

2 minutes ago, wimvb said:

Nope, the lenses themselves are made from this semiconductor. Germanium has about 50% transparency for wavelengths longer than 2 um. As a bit of trivia, germanium is also valued as a material to make amplifier transistors in particularly electric guitar amplifiers. According to a guitar playing former colleague.

hi Wim, yes i know- we have an Flir camera at work and it’s weird that the lens is opaque and silvery looking! I meant are the JWST filters made from Germanium?  Yes Germsnium transistors are a bit valve like i think when overdriven- softer sounding  than silicon- Brian May’s trademark sound is from an old HMV germanium transistor amp that i think John Deacon modified for him in the early days of Queen.

Mark

[wimvb]

1 minute ago, markse68 said:

I meant are the JWST filters made from Germanium?

I found an article on Researchgate that says substrates are either ZnSe (zinc selenide) or CdTe (cadmium telluride), depending on which wavelengths they need to cover. Don’t know if that’s what they ended up using.

[Macavity]

1 hour ago, saac said:

Re gravitational lensing and reconstruction of image - 
https://skyandtelescope.org/astronomy-news/incredible-resolution-reconstructed-galaxy-pushes-hubbles-limits/

Thanks! Was I the only one who thought (Albeit somewhat cogniscent of gravitational lensing): Aaaargh! lol. 🥳

Their "Ring Nebula" image... with the LONE edge-wise Galaxy (finally resolved as such) was less challenging!
Relatable appeal? The central star sort-of answers my question re. the (v.approximate!) magnitudes of stuff. 😎

 

[maw lod qan]

I saw the area of the deep field image described as being the equivalent of you holding a grain of sand at arms length.

It was my understanding that the Hubble's deep field was taken of an area there was nothing visible in from Earth.

I hope they just pick another area that is blank to us and do it again. To think there is something every where you look gives a new meaning to the term infinite!

[saac]

27 minutes ago, maw lod qan said:

I saw the area of the deep field image described as being the equivalent of you holding a grain of sand at arms length.

It was my understanding that the Hubble's deep field was taken of an area there was nothing visible in from Earth.

I hope they just pick another area that is blank to us and do it again. To think there is something every where you look gives a new meaning to the term infinite!

Reminds me of a line from one of my favourite poems "To See A World" (from Auguries of Innocence) by William Blake 

To see a World in a Grain of Sand

and a Heaven in a Wild Flower,

Hold infinity in the palm of your hand

And Eternity in an hour 

 

Jim 

Edited July 14, 2022 by saac

[Padraic M]

2 hours ago, maw lod qan said:

I saw the area of the deep field image described as being the equivalent of you holding a grain of sand at arms length.

 

I have to say that this description didn't really mean that much to me so I tried an experiment. 

From here https://webbtelescope.org/contents/media/images/2022/038/01G7JGTH21B5GN9VCYAHBXKSD1 we know that the Webb Deep Field image is about 2.4 arcmin across. From Stellarium, I can see that M51 is approximately 11'12" x 6'54" - so almost 7' across in its narrowest dimension.

Here's an extract from my latest M51 image with an overlay of what I believe to be the field of view of the Webb NIRCam wide field image. 

NIRCam's pixel scale is 0.031" (short wavelength channel) or 0.063" (long wavelength channel).

[DaveS]

 

[johnfosteruk]

17 minutes ago, DaveS said:

 

Been waiting for this, cheers Dave.

[DaveS]

I'll watch it tomorrow, as I'm for bed.

[niallk]

[Sunshine]

Some will find this page on NASA website interesting, it outlines Webb’s objectives and goes into the how and why it is an infra red telescope. Under each topic one must click the “read more” tab to expand.

https://webb.nasa.gov/content/science/