James Webb Telescope

smartcooky said:
The Webb team hopes to see the mirrors cool by an additional 0.5 to 2 kelvins.​

What do they mean by "mirrors". Do they mean the primary and secondary mirrors, or are they talking about the mirror segments? Usually, when they refer to the "mirror" they are talking about primary as a whole.
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Pretty sure that they mean the individual mirror segments of the primary mirror. The secondary mirror is already quite cool (29.4 kelvins).
 
Puppycow said:
Pretty sure that they mean the individual mirror segments of the primary mirror. The secondary mirror is already quite cool (29.4 kelvins).
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I'm not sure about that.

For one thing, in previous blog entries they have referred to the segments as "segments" or "mirror segments" . For another, do they say that they hope the "mirrors" will cool down by up to 2K. Does that mean all of the segments, or the mirrors.
 
acbytesla said:
Right now is the commissioning phase of the instruments. This seems like a nebulous term that could cover anything.
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Basically, running each instrument through its paces with various settings, filters, etc. Also, they are going to moving the telescope focus to verify that pointing at new targets doesn't affect instrument performance.

More info (a little):
https://blogs.nasa.gov/webb/2022/04/28/nasas-webb-in-full-focus-ready-for-instrument-commissioning/

ETA: Same link Mike posted above.
 
https://www.universetoday.com/15568...compare-webb-to-other-infrared-observatories/

Now, We can Finally Compare Webb to Other Infrared Observatories

The images released by the James Webb Space Telescope team last week aren’t officially ‘first light’ images from the new telescope, but in a way, it feels like they are. These stunning views provide the initial indications of just how powerful JWST will be, and just how much infrared astronomy is about to improve.

The images were released following the completion of the long process to fully focus the telescope’s mirror segments. Engineers are saying JWST’s optical performance is “better than the most optimistic predictions,” and astronomers are beside themselves with excitement.

“It hasn’t broken the laws of physics, but does lie at the very best end of possibilities thanks to the extraordinary efforts of many over decades,” said Mark McCaughrean, the European Space Agency’s Senior Advisor for Science & Exploration and part of JWST’s Science Working Group, on Twitter.
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a_unique_person said:
There's just more fuzzy blobs back there I can't quite make out now.
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I can see a lot more detail.

I wonder if everything is going be just red with this telescope?

It doesn't see blues and greens right?

I guess I should have expected that. It's not an optical telescope.
 
Puppycow said:
I can see a lot more detail.

I wonder if everything is going be just red with this telescope?

It doesn't see blues and greens right?

I guess I should have expected that. It's not an optical telescope.
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It is an optical telescope, it just operates in the infrared range, rather than the visible range. The images have to be artificially adjusted so that we can see them at all. Which means, I guess, that if an image contains a range of wavelengths in the infrared spectrum, it will also have a range of wavelengths when it is shifted to the visible spectrum.

I expect that it's more complicated than that, though.
 
Puppycow said:
I can see a lot more detail.

I wonder if everything is going be just red with this telescope?

It doesn't see blues and greens right?

I guess I should have expected that. It's not an optical telescope.
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I think unique person is describing more frustration by bringing to view objects we will never quite resolve.
 
arthwollipot said:
It is an optical telescope, it just operates in the infrared range, rather than the visible range. The images have to be artificially adjusted so that we can see them at all. Which means, I guess, that if an image contains a range of wavelengths in the infrared spectrum, it will also have a range of wavelengths when it is shifted to the visible spectrum.

I expect that it's more complicated than that, though.
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Probably, it'd be interesting if anyone knows, but to me (which doesn't mean much) it seems fairly straight forward.

If the visible spectrum is between 380 nm and 750 nm wavelengths, and the telescope is (let's just assume) only observing wavelengths greater than 750 nm, then to represent that data visually, you need a function to transpose all those wavelengths to somewhere in the visible spectrum.

It seems they could just just a range between 350 and 750 nm arbitrarily. For instance 400 to 500, which would make all the stars and galaxies appear somewhere between blue and green (I think).

Since such an image would be very misleading, they seem keep the transposed range of wavelengths between yellow and red.
 
Mike Helland said:
Probably, it'd be interesting if anyone knows, but to me (which doesn't mean much) it seems fairly straight forward.

If the visible spectrum is between 380 nm and 750 nm wavelengths, and the telescope is (let's just assume) only observing wavelengths greater than 750 nm, then to represent that data visually, you need a function to transpose all those wavelengths to somewhere in the visible spectrum.

It seems they could just just a range between 350 and 750 nm arbitrarily. For instance 400 to 500, which would make all the stars and galaxies appear somewhere between blue and green (I think).

Since such an image would be very misleading, they seem keep the transposed range of wavelengths between yellow and red.
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It does see some visible-to-humans light, don't know if the images released so far are just the visible light images it does see or false coloured.

I am sure they will do as has been done with Hubble and false colour images for public release, and I don't think it is misleading if they do that.
 
Darat said:
It does see some visible-to-humans light, don't know if the images released so far are just the visible light images it does see or false coloured.

I am sure they will do as has been done with Hubble and false colour images for public release, and I don't think it is misleading if they do that.
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Makes sense to me. For public interest, translate the spectra into ones that we can differentiate using our spectra-differentiating sense, even though the image comes from photons outside our visual range. For scientific purposes, other more precise encodings can be used instead.

The light of interest it's supposed to be observing, once it's fully in operation, is not visible to humans. Any visible-to-humans light it might sense is just in the way (unless it discovers unexpected and by current cosmological models impossible anomalies).
 
Depends on the instrument. NIRCAM can reach into the reds, but I think the images released so far are from MIRI, which can't get close. Shortest it is supposed to see is 5 microns, or 5000 nm. We won't see anything longer than 800 nm.

The comparison image above says 7.7 microns. I suspect the images taken thus far are single filter captures, so there's no wavelength discrimination to apply false coloration to, just a simple gradient for intensity. That's common for gathering the highest resolution possible.
 
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