Webb mirror alignment begins with first photons detected by instrument
With the detection by one instrument of the first photons traveling through all of the mirrors of the James Webb Telescope the alignment of its many mirror segments begins.
This week, the three-month process of aligning the telescope began – and over the last day, Webb team members saw the first photons of starlight that traveled through the entire telescope and were detected by the Near Infrared Camera (NIRCam) instrument. This milestone marks the first of many steps to capture images that are at first unfocused and use them to slowly fine-tune the telescope. This is the very beginning of the process, but so far the initial results match expectations and simulations.
The article at the link provides a very detailed description of the step-by-step process used by engineers to align the eighteen segments of the primary mirror.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
With the detection by one instrument of the first photons traveling through all of the mirrors of the James Webb Telescope the alignment of its many mirror segments begins.
This week, the three-month process of aligning the telescope began – and over the last day, Webb team members saw the first photons of starlight that traveled through the entire telescope and were detected by the Near Infrared Camera (NIRCam) instrument. This milestone marks the first of many steps to capture images that are at first unfocused and use them to slowly fine-tune the telescope. This is the very beginning of the process, but so far the initial results match expectations and simulations.
The article at the link provides a very detailed description of the step-by-step process used by engineers to align the eighteen segments of the primary mirror.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
So, is Webb far from that new Trojan?
Q:
What wavelength are we talkin’ about?
Just pondering out loud:
When I hear “photons” I generally think visible light, even though I understand that part of the EM spectrum is fairly small, and this is an infra-red telescope.
(This is sorta how our institutions lie by omission & framing, ‘they imply, and you infer.’)
wayne: Gosh you are right. Photons suggest visible light. However, visible light I assume will also travel through the mirrors, along with infrared. It is the instruments that will read the infrared as designed.
Mr. Z.,
–I have been highly leery of this telescope (time & cost mainly, and of course, ‘what could possibly go wrong….) but I am very pleased everything appears to be proceeding as planned.
–You’ve mentioned numerous times, paraphrasing broadly –we’ll get great images but they won’t be optical pictures, like the Hubble.
The Interweb tells me:
“Photon” = ‘a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass.”
So, by definition that covers the entire EM spectrum. In general parlance however, ‘photon’ smacks of visible light, or is that just me?
Wayne: Actually, this definition is correct, though your sense is also right. Generally photons are use referring to visible light, but when it comes to Webb they will clearly be gathering photons as well.
And like you, I have been very unhappy with this telescope project for years. Too expensive, does not replace Hubble, sucked all the money from every other astrophysical space telescope for more than two decades.
However, thank God everything now appears to be working, and it will finally be able to do real science in space, most of it cutting edge.
I was just thinking.
Since we now have the technology to align the mirror segments while in space couldn’t we add more segments and have the telescope unfold into a larger diameter?
I know that having a larger structure will add to the thermal distortion on the system but with constant computer corrections going on wouldn’t it at least be possible?
In terms of adding segments, I doubt it. The alignment mechanisms are amazingly precise and delecate. Tying in more mirror segments while in a difficult environment (rather than in a precisely controlled one) risks detuning the entire system.
That was a good explanation of what they’re doing but I guess they necessarily glossed over the how of coarse and fine phasing.
How the heck do you match something on the scale of 50 nanometers. There’s no way we can be talking about physical mirror movements past image stacking, can we?
This article also disproves the fake news of the first leaked Webb image. The out of focus, “remove before flight” image. ;)
Not on the Web telescope but on future ones.
Nasa can’t even figure out how to refuel their own satellites just to keep them operational longer. let alone adding more mirrors to this one.
pzatchok,
There may have been weight limitations. In addition, the more complex the system the harder to control.
Now that they made one, making another will cost one 1/100 as much.
They can wait to see what problems arise and make the necessary adjustments for additional telescopes upgraded for a better function.
Hopefully inspiring the creation of a bunch of large telescopes sensing the universe in every wavelength. (There could be a problem with ice and dust buildup from the solar wind on the cold side mirrors)
Nobel laureate explains his project, James Webb telescope explained / simplified. Smarter every day.
https://m.youtube.com/watch?v=4P8fKd0IVOs
Photons with the wave length that is visible to our eyes run from 375 nm to 775 nm.
The web can see 600 nm to 28,500 nm (or .6 microns [bright red] to 28.5 microns [very dull, dim red] ) that should be sufficient to see the known red stars and red shifted galaxy’s we can see with our eyes… and all of the deeper red galaxies and supernova/space dust that we cannot.
https://jwst.nasa.gov/content/about/faqs/facts.html
It is said that carbon dioxide reflects heat at the 700 nm range… That’s the same wavelength of light reflecting off of clouds just before sunrise. (Can you feel all that heat?) It would probably take a detector as large as the James Webb telescope to detect, collect and analyze the accurate amount of heat reflected off those clouds, perhaps even detect reflection off of carbon dioxide molecules? If it can be measured, it would put the greenhouse theory to a rest as being real… Or too small of a number to make an actual difference. (It would be interesting to see what kind of picture of the sun reflecting off the clouds this telescope would make).
Forgot to mention that there is about a golf ball sized amount of gold covering the beryllium on the reflector. Beryllium is perfect for a mirror base because it does not shrink in the cold, Gold does. It’ll be interesting to see if this bi-metal strip can hold it shape… I think it will because gold is so soft. We will see overtime if distortions creep in.