Starship Asterisk*

JWST: Ghosts and Mirrors

Explanation: Ghosts aren't actually hovering over the James Webb Space Telescope. But the lights are out as it stands with gold tinted mirror segments and support structures folded in Goddard Space Flight Center's Spacecraft Systems Development and Integration Facility clean room. Following vibration and acoustic testing, bright flashlights and ultraviolet lights are played over the stationary telescope looking for contamination, easier to spot in a darkened room. In the dimness the camera's long exposure creates the ghostly apparitions, blurring the moving lights and engineers. A scientific successor to Hubble, the James Webb Space Telescope is optimized for the infrared exploration of the early Universe. Its planned launch is in 2018 from French Guiana on a European Space Agency Ariane 5 rocket.

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Successor (or rather complement) to the Hubble, which followed Copernicus, a high-spectral-resolution ultraviolet telescope conceived by Lyman Spitzer Jr. Copernicus was a huge success, but when launched, and turned on, and pointed to a pre-selected BRIGHT UV star....they got NO signal! They agonized for hours over what could possibly have gone wrong, and finally Lyman said "let's go to bed and we'll figure it out in the morning." When they all reassembled, Lyman said "we launched it with the spectrometer set at the wavelength of the deepest strong hydrogen line! Let's start moving in wavelength! They did so, and ... a beautiful profile of a UV spectral line appeared as they scanned! Good luck to JWST!

Hope it performs as awesome as it looks...

:---[===] *

Which reminds me....I was a graduate student in 1963 and James Webb was visiting the Department of Astrophysical Sciences at Princeton, and Lyman Spitzer and Martin Schwarzschild invited us graduate students to join them with Webb for dinner at the Balt. Webb (of course) was then Administrator of NASA.
So many telescopes have been named for astronomers; now, at last, one for ... an administrator! Who knows? Maybe, some day, an Engineer might...

heehaw wrote:
Which reminds me....I was a graduate student in 1963 and James Webb was visiting the Department of Astrophysical Sciences at Princeton, and Lyman Spitzer and Martin Schwarzschild invited us graduate students to join them with Webb for dinner at the Balt. Webb (of course) was then Administrator of NASA.

You were an astronomy grad student in 1963 How did that turn out?

I was an astronomy grad student at the Univ. of Md. in 1970 when I got to meet Lyman Spitzer and the irrepressible Martin Schwarzschild. I was subsequently drafted into the Army and ended up working on weather satellites for NOAA (where my mantra was 'follow the water vapor').

I CANNOT wait for the results to come in..once it is successfully implemented!!!!

This thing just better works.

crossed wrote:
This thing just better works.

• Or there will be spell to pay

neufer wrote: You were an astronomy grad student in 1963
I was an astronomy grad student at the Univ. of Md. in 1970 when I got to meet Lyman Spitzer and the irrepressible Martin Schwarzschild. I was subsequently drafted into the Army and ended up working on weather satellites for NOAA (where my mantra was 'follow the water vapor').

You ask how did that turn out? Great! Got my PhD and a postdoc at NRL and on to JHU! As a Canadian I was free of the draft, thank God.

heehaw wrote:
Got my PhD and a postdoc at NRL and on to JHU!

My dad got his physics PhD at JHU and later my eldest daughter got her masters in teaching there.

So what research did you do?

So, the telescope, "is optimized for the infrared exploration..." Does this mean that it will be able to take visible light images? If not, why not? It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

FLPhotoCatcher wrote:So, the telescope, "is optimized for the infrared exploration..." Does this mean that it will be able to take visible light images? If not, why not? It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

I can only suggest you read up on what JWST's actual range of wavelengths will be. Infrared is not analogous to, say, one color of the visible rainbow. It's more like an entire rainbow all on its own. There is nothing at all narrow about it except for specific filters, such as the Paschen-alpha filter, which is something like Hydrogen-alpha's infrared cousin.

FLPhotoCatcher wrote:So, the telescope, "is optimized for the infrared exploration..." Does this mean that it will be able to take visible light images? If not, why not? It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

It has a camera that has some sensitivity at the red end of the spectrum, so in a sense it can take "visible light" images. For instance, it has sensitivity to H-alpha at 656 nm, but has no narrowband filters for this line.

The wavelength range for the JWST is much wider than that of any visible light instrument (such as Hubble). The primary reason that it is limited to wavelengths longer than 600 nm (and thus largely outside the visible range) is because of the nature of the detectors used in the cameras. Ordinary silicon detectors such as those used by Hubble (and in our everyday digital cameras) are not sensitive outside of visible and very near IR. So a near- to mid-range IR sensor is made of more exotic materials, not sensitive to visible light. In order for the JWST to image visible light, they would have needed another camera. Perhaps they would have considered this, except for the fact that all the other optics, including the main mirror, are made of materials that are not well suited to reflecting or passing shorter wave light. Nor is the adaptive optics system well suited to short wavelengths.

In short, it just isn't practical to make a single instrument that covers the range from short wavelength visible through mid-IR, because all of the manipulation and detection technology is different. It's like saying that your radio should also serve as a microscope. Sure, both detect and manipulate electromagnetic radiation. But they do so very differently.

FLPhotoCatcher wrote:It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

Infrared vision enables us to see heat and to see through dust. Being able to extend our vision is hardly "a waste".

Bruce

BDanielMayfield wrote:

FLPhotoCatcher wrote:It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

Infrared vision enables us to see heat and to see through dust. Being able to extend our vision is hardly "a waste".

That might be confusing. In fact, IR lets us see very low temperatures compared with shorter wavelength instruments.

Chris Peterson wrote:

BDanielMayfield wrote:

FLPhotoCatcher wrote:
It seems kind-of a waste to make such a good telescope that only sees in such a narrow wavelength.

Infrared vision enables us to see heat and to see through dust. Being able to extend our vision is hardly "a waste".

That might be confusing. In fact, IR lets us see very low temperatures compared with shorter wavelength instruments.

Mostly, though, the JWST will allow us to see the most distant galaxies whose starlight is now in the IR.

neufer wrote:

Chris Peterson wrote:

BDanielMayfield wrote: Infrared vision enables us to see heat and to see through dust. Being able to extend our vision is hardly "a waste".

That might be confusing. In fact, IR lets us see very low temperatures compared with shorter wavelength instruments.

Mostly, though, the JWST will allow us to see the most distant galaxies whose starlight is now in the IR.

And of course, in that application, we could argue that JWST is seeing in visible light!