James Webb Telescope

smartcooky said:
As far as I know the Fine Steering Motor and the Instrument Radiator do not have specific target temperatures, they are passively cooled by being on the shadow side of the sun-shield, while three of the instruments are semi-actively cooled by the Instrument Radiator, the fourth, MIRI is actively cooled by the cryo-cooler.

The Primary Mirror is expected to be below 50K, but keep in mind that this is just an average, because its not "a" mirror, it is 18 mirrors. The final temperatures will still have a spread of 15 to 20 kelvins across all 18. While 40K would be great, is not vital in the way that the instrument temperatures are.

I read something interesting a while ago about how the cooling works for NIRCam, NIRSpec and NIRISS using the sun-shield. Apparently the amount of energy (in milliwatts) that gets through the sun-shield, plus the heat generated by electronics of the three instruments, is exactly balanced against the loss of heat into space, in order to achieve a "steady state temperature". They calculated what the heat loss to space would be, and the heat that would be would be generated by the electronics, and then designed the sun-shield to allow just the right amount of heat through to keep the instrument temperatures stable.

The more I read about the JWST, the I am gobsmacked by the extraordinary level of engineering involved.
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Me too! I was so pessimistic about this project. I felt sure that something would go horribly wrong. I have a feeling it is going to show us galaxies that are many more billions of light years farther away than we have ever seen before.

What I really love about the JWST is that anyone from anywhere has the opportunity to get time on the telescope. All you have to do is present a subject interesting enough to the committee. The selection process is blind.
 
Green = Instrument target temperature reached

Frame and mirror
Primary Mirror -231° 43K
Instrument Radiator -237° (37K)
Fine Steering Motor -241° (33K)

Instruments
MIRI -238° (35K)
NIRcam-235° (38K)
NIRSpec-239° (35K)
FGS/NIRISS -234° (39K)

MIRI's temperature still on track to reach its target temperature of 7K in about 8-10 days
 
Turns out James Webb was a homophobe who was involved in persecution of LGBTQ+ employees at the State Department and at NASA.

New Revelations Raise Pressure on NASA to Rename the James Webb Space Telescope (Scientific American, April 4, 2022)

E-mailed exchanges show the space agency’s internal struggle to address pleas to change the controversial name of its latest, greatest observatory


Sadness. Disappointment. Frustration. Anger. These are some of the reactions from LGBTQ+ astronomers over the latest revelations regarding NASA’s decision not to rename the James Webb Space Telescope (JWST), given that the agency long had evidence suggesting its Apollo-era administrator James Webb was involved in the persecution of gay and lesbian federal employees during the 1950s and 1960s.

The new information came to light late last month when nearly 400 pages of e-mails were posted online by the journal Nature, which obtained the exchanges under a Freedom of Information Act (FOIA) request. Since early last year, four researchers have been leading the charge for NASA to alter the name of the $10-billion flagship mission, launched in December 2021, which will provide unparalleled views of the universe. The e-mails make clear that, behind the scenes, NASA was well aware of Webb’s problematic legacy even as the agency’s leadership declined to take his name off the project.

...

Originally known as the Next Generation Space Telescope, JWST was rechristened for Webb in 2002, a decision undertaken by Sean O’Keefe, NASA’s administrator at the time. Little was known then about Webb’s role in a period of mid-20th-century American history known as the Lavender Scare—a McCarthy-like witch hunt in which many gay and lesbian federal employees were seen as national security risks and subsequently surveilled, harassed and fired.

Prior to leading NASA, Webb was second-in-command at the U.S. Department of State. In a September 3, 2021, e-mail Nature obtained through FOIA, a redacted writer notes that archival documents paraphrased in a 2004 history book say, “Webb met with President [Harry S.] Truman on June 22, 1950 in order to establish how the White House, the State Department, and the Huey Committee might ‘work together on the homosexual investigation.’” A large number of LGBTQ+ workers were fired from the State Department before Webb resigned from his position there in 1952.

Critics say homophobia followed Webb to NASA. During his tenure as the agency’s administrator between 1961 and 1968—a critical time in its preparations to land astronauts on the moon—a suspected gay employee, Clifford Norton, was interrogated for hours about his sexual history by NASA’s security chief and ultimately fired for “immoral, indecent, and disgraceful conduct.” This was part of the basis for calls to rename JWST, which NASA responded to by conducting an internal investigation into Webb’s complicity in such actions.

On September 27, 2021, current agency administrator Bill Nelson released a one-sentence statement saying, “We have found no evidence at this time that warrants changing the name of the James Webb Space Telescope.” The announcement seems odd, given that, as early as April 2021, one redacted author in the newly released e-mails noted that the official who fired Norton testified the termination came about because his advisers had told him that dismissal for homosexual conduct was considered a “custom within the agency.”
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arthwollipot said:
Turns out James Webb was a homophobe who was involved in persecution of LGBTQ+ employees at the State Department and at NASA.

New Revelations Raise Pressure on NASA to Rename the James Webb Space Telescope (Scientific American, April 4, 2022)
Click to expand...

Sadness. Disappointment. Frustration. Anger. These are some of the reactions from LGBTQ+ astronomers over the latest revelations regarding NASA’s decision not to rename the James Webb Space Telescope (JWST), given that the agency long had evidence suggesting its Apollo-era administrator James Webb was involved in the persecution of gay and lesbian federal employees during the 1950s and 1960s.
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Wasn't homosexuality illegal in the US in the 50s and 60s?
 
arthwollipot said:
Turns out James Webb was a homophobe who was involved in persecution of LGBTQ+ employees at the State Department and at NASA.

New Revelations Raise Pressure on NASA to Rename the James Webb Space Telescope (Scientific American, April 4, 2022)
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NASA should resist any and all pressure to change, and here's why.

Firstly, this was NASA policy at the time. Whoever was in Webb's position (NASA Administrator) would have been required to enforce that policy or lose his job, and his replacement would then be tasked with enforcing the policy.

Secondly. James Webb was the NASA Administrator from February 14, 1961 until October 7, 1968. At that time, being a homosexual was still considered morally corrupt, and was still a criminal offence in Florida. This remained the case until 1971 when the Florida Supreme Court struck down their "crime against nature" statute.

I'm not saying what James Webb did was right, only that it was understandable given the prevailing attitudes of the time. We ought not hold people in the past responsible for the moral standards of today.

“The past is a foreign country; they do things differently there.”
-LP Hartley
 
I will say this: I'm not a fan of the process by which the telescope was named after Webb in the first place. NASA's administrator at the time made a unilateral decision without seeking any outside input, apparently. And he chose to name it after a previous NASA administrator.

I will also note that this was during the George W. Bush Administration, which was decidedly unfriendly to gays. Back then, Republicans still considered gay-bashing to be a politically winning issue.

But that's water under the bridge, and the question before us now is whether to rename a telescope that most people already know the name of. There would inevitably be a big stink about "political correctness" too, and some people might refuse to go along with the name change.

And where does it end? Are we to also erase Washington and Jefferson from our money because they owned slaves? Should we also rename our nation's capital as well as that state in the Pacific Northwest?

I feel like we had this debate already and bringing it up again is just picking at a scab.
 
acbytesla said:
I have a feeling it is going to show us galaxies that are many more billions of light years farther away than we have ever seen before.
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Since the oldest galaxy we have a fuzzy photo of formed 400 million years after the BB, don’t get your hopes up.
:D

Edit: Or am I wrong? Could a galaxy have formed early enough to have travelled far enough away, to now be billions of light years further from us than one that formed 400 million years after the BB? I actually don’t know. It just sounded wrong when I read it. Oops.
 
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No, I think you’re right.

The upper limit on how far away anything we could see would be is the age of the universe. And actually less than that that, because it took some time for the first stars and galaxies to form, and there was an early period when everything was opaque.
 
Puppycow said:
No, I think you’re right.

The upper limit on how far away anything we could see would be is the age of the universe. And actually less than that that, because it took some time for the first stars and galaxies to form, and there was an early period when everything was opaque.
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It's worse than that. Because of the accelerating expansion of spacetime, there's a horizon beyond which everything is accelerating away from us at faster than the speed of light. So light emitted from over that horizon can never get to us.
 
It seems the edge of the observable universe is about 46 billion ly away and the furthest galaxy, GN-z11 about 32 billion ly, so you have 14 difference.
The question is when the first galaxy (in the observable universe) formed, it might be a few but not many billion ly further.
 
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Cheetah said:
It seems the edge of the observable universe is about 46 billion ly away and the furthest galaxy, GN-z11 about 32 billion ly, so you have 14 difference.
The question is when the first galaxy (in the observable universe) formed, it might be a few but not many billion ly further.
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I assume what you are saying is that in the present day, this galaxy is about 32 billion ly distant?

However, what we see, of course is the light that left it about 13.4 billion years ago, and since light travels at the speed of light, it would have traveled a distance of 13.4 billion light-years in that time.

https://www.u-tokyo.ac.jp/focus/en/press/z0508_00153.html

“From previous studies, the galaxy GN-z11 seems to be the farthest detectable galaxy from us, at 13.4 billion light years, or 134 nonillion kilometers (that’s 134 followed by 30 zeros),” said Kashikawa. “But measuring and verifying such a distance is not an easy task.”
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We are separated from it in both space and time, effectively, as we can only see it as it was 13.4 billion years ago.

Due to the expansion of the universe, at the present time it is likely much farther away than that. I assume that is what you are saying?
 
This point has started a train of thought for me though.

Nobody really knows how large the universe is, do they?

We can estimate the size of the observable universe, but not the entire universe. I don’t imagine that it is infinitely large, but what do I know?

For example, how big was the universe 400 million years after the Big Bang, when the light from the most distant galaxies in the observable universe began its journey to us?
 
Puppycow said:
I assume what you are saying is that in the present day, this galaxy is about 32 billion ly distant?
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Yes.
Puppycow said:
We can estimate the size of the observable universe, but not the entire universe. I don’t imagine that it is infinitely large, but what do I know?
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I imagine infinities, singularities and real paradoxes not to be part of the universe, but what do I know?
 
Puppycow said:
This point has started a train of thought for me though.

Nobody really knows how large the universe is, do they?

We can estimate the size of the observable universe, but not the entire universe. I don’t imagine that it is infinitely large, but what do I know?

For example, how big was the universe 400 million years after the Big Bang, when the light from the most distant galaxies in the observable universe began its journey to us?
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I'm waiting to see what the JWST tells us. I'm expecting the observable universe to grow substantially. As for the universe being infinite. It appears to be infinite, but so did the oceans a few hundred years ago. We can see only as far as we can see.
 
That’s just it, our observable universe cannot grow using a better telescope. We will just have more detail.
 
Puppycow said:
This point has started a train of thought for me though.

Nobody really knows how large the universe is, do they?

We can estimate the size of the observable universe, but not the entire universe. I don’t imagine that it is infinitely large, but what do I know?
Click to expand...

It might be infinitely large. It turns out this question is directly connected to whether or not it will expand forever or whether it will eventually collapse again, which is in turn connected to how fast it has expanded so far. IIRC, from what we can tell, we're close to the boundary between those two scenarios. I believe we actually can put an estimate for a lower limit on the sized of the universe, based on its expansion rate. And it's got to be pretty big, much bigger than what we can see. But we cannot exclude it being infinite. And if it's infinite, it was always infinite, even at the beginning.
 
Cheetah said:
That’s just it, our observable universe cannot grow using a better telescope. We will just have more detail.
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Or wait. Waiting expands the visible universe, though there is a limit to this as well.
 
Yes it’s getting bigger all the time due to expansion, but that has nothing to do with the quality of instrument we are using to observe it with.
The observable universe has a physical limit we can already see, the CMB.
 
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