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Old 25th December 2021, 02:53 AM   #201
Mike Helland
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JWST Where is Webb?

https://jwst.nasa.gov/content/webbLa...ereIsWebb.html

That's pretty cool.
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Old 25th December 2021, 03:26 AM   #202
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Two hours to go!!

Here's a livestream from Launch Pad Astronomy:

https://www.youtube.com/watch?v=pVKzZ89N2Ks

Not much to see yet though. Apparently the coverage begins about an hour before launch.
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Old 25th December 2021, 03:28 AM   #203
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Originally Posted by Mike Helland View Post
JWST Where is Webb?

https://jwst.nasa.gov/content/webbLa...ereIsWebb.html

That's pretty cool.
That's interesting. I'll keep that tab open once it launches.
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Old 25th December 2021, 03:53 AM   #204
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Originally Posted by Puppycow View Post
Two hours to go!!

Here's a livestream from Launch Pad Astronomy:

https://www.youtube.com/watch?v=pVKzZ89N2Ks

Not much to see yet though. Apparently the coverage begins about an hour before launch.
Just before midnight NZ
This is amazing for chrissakes
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Old 25th December 2021, 04:25 AM   #205
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Originally Posted by Samson View Post
I have a friend who is a serious historian, but likes evidence. He knows the big bang is nonsense because you can't get something from nothing.

The telescope is to see the big bang.
1. Historian does not = cosmologist.

2. You have an amazingly, almost moronically, simplistic view of the purpose and uses of the Webb.
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Old 25th December 2021, 04:34 AM   #206
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Originally Posted by Steve View Post
1. Historian does not = cosmologist.

2. You have an amazingly, almost moronically, simplistic view of the purpose and uses of the Webb.
Americans do not do irony, but some nations do, lol
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Old 25th December 2021, 04:42 AM   #207
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Originally Posted by Samson View Post
Americans do not do irony, but some nations do, lol
Is this in any way connected to my post that you quoted? Appears that it is not.
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Old 25th December 2021, 04:54 AM   #208
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Originally Posted by Steve View Post
Is this in any way connected to my post that you quoted? Appears that it is not.
Yes it is.
I responded to a post by referring to an actual person. The irony is embedded in knowing this telescope can't resolve the big bang.
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Old 25th December 2021, 05:00 AM   #209
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Here's the official NASA feed:

https://www.youtube.com/watch?v=7nT7JGZMbtM


Launch is about 20 minutes away.
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Old 25th December 2021, 05:30 AM   #210
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Originally Posted by Samson View Post
Yes it is.
I responded to a post by referring to an actual person. The irony is embedded in knowing this telescope can't resolve the big bang.
What do you mean by *resolve* the big bang?

What relevance did your reference to Americans have to my post?

What qualifications does your *friend*, a *serious* historian (as opposed to a comical one, no doubt) have to comment on the purpose of the Webb? Or on the status of the big bang?

Your comment was nothing more than a useless, and doubtful, anecdote.
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Old 25th December 2021, 05:31 AM   #211
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Yay!

Everything 'nominal' so far.
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Old 25th December 2021, 05:36 AM   #212
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Yay! Didn’t blow-up!!!
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Old 25th December 2021, 05:53 AM   #213
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Saw the solar panels deploy. Our last view of the telescope!

This is going great so far.
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Old 25th December 2021, 05:57 AM   #214
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The telescope is now on its own. The rocket at least did its job perfectly.

Now if anything goes wrong from here on, its not on the rocket company.
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Old 25th December 2021, 06:34 AM   #215
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“It’s a great day for planet Earth.” - Bill Nelson, NASA Administrator.

“We have delivered a Christmas gift today to humanity, to people, to NASA, but also to all the people in this world.” - Josef Aschbacher, ESA Director General

“Historians of the future will divide our understanding of the cosmos into eras Before Webb, and After Webb.” - Michelle Thaller, astronomer
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Old 25th December 2021, 06:40 AM   #216
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Great, now we have to wait months if not years for this thing to fail.


>>>>disclaimer>>>> When President Kennedy did the "We'll go to the moon." My opinion was 'yeah that's gonna happen.'
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Old 25th December 2021, 07:17 AM   #217
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Originally Posted by Darat View Post
Yay! Didn’t blow-up!!!
It will. The Jewish space lasers haven't launched their attack yet.
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Old 25th December 2021, 07:26 AM   #218
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great.
James Webb will take hi-res pictures of God and all of us atheists are going to have egg on our faces.
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Old 25th December 2021, 07:31 AM   #219
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Originally Posted by The Great Zaganza View Post
great.
James Webb will take hi-res pictures of God and all of us atheists are going to have egg on our faces.
Nah - it will be Adams’ “We apologize for the inconvenience”
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Old 25th December 2021, 08:46 AM   #220
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This event, imho, is akin to 'One small step...'
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Old 25th December 2021, 10:19 AM   #221
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Originally Posted by Samson View Post
Yes it is.
I responded to a post by referring to an actual person. The irony is embedded in knowing this telescope can't resolve the big bang.
Hardly surprising, and a pretty silly thing to say, since the JWST wasn't built to look back to the Big Bang. We have known this is not possible since the early 1960s when the CMB was discovered. It is impossible to see back any further than about 380,000 years after the Big Bang, because because it was "dark" as in there was no light.

https://jwst.nasa.gov/content/science/firstLight.html
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Old 25th December 2021, 10:27 AM   #222
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Originally Posted by Samson View Post
I have a friend who is a serious historian, but likes evidence. He knows the big bang is nonsense because you can't get something from nothing.

The telescope is to see the big bang.
You might also wish to explain to your non-cosmologist friend that expansion cosmology says nothing about something coming from nothing.
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Old 25th December 2021, 12:44 PM   #223
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Originally Posted by welshdean View Post
This event, imho, is akin to 'One small step...'
I truly hope you are right.
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Old 25th December 2021, 01:18 PM   #224
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Originally Posted by Samson View Post
I have a friend who is a serious historian, but likes evidence. He knows the big bang is nonsense because you can't get something from nothing.
The last time I heard that argument made it was made by Ginger Baker. And while I have great respect for his drumming, his pronouncements on cosmology are worth about as much as your friend's - ie not a lot.
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Old 25th December 2021, 01:23 PM   #225
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Originally Posted by smartcooky View Post
Hardly surprising, and a pretty silly thing to say, since the JWST wasn't built to look back to the Big Bang. We have known this is not possible since the early 1960s when the CMB was discovered. It is impossible to see back any further than about 380,000 years after the Big Bang, because because it was "dark" as in there was no light.

https://jwst.nasa.gov/content/science/firstLight.html
It’s alright, someone added a torch….
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Old 25th December 2021, 04:13 PM   #226
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Quote:
“This telescope is so powerful that if you were a bumble bee 240,000 miles away, which is the distance between the Earth and the moon, we will be able to see you,” said John Mather, the mission’s senior project scientist at NASA’s Goddard Space Flight Center in Maryland.
https://spaceflightnow.com/2021/12/2...e-cosmic-dawn/

This just seems mind-blowing, to me. How could it possibly reconcile an object so small at that distance?
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Old 25th December 2021, 05:20 PM   #227
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Originally Posted by Mike Helland View Post
JWST Where is Webb?

https://jwst.nasa.gov/content/webbLa...ereIsWebb.html

That's pretty cool.
That's a great site.

I do have a question on the day 30+ orbit.

The orbit for Webb is roughly circular at the L2 Lagrange point. Since the L2 point doesn't have mass there, the Webb is not orbiting a body in space (like the earth). So, how does it maintain its orbit without constant thruster firing? It must be in constant acceleration, no?
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Old 25th December 2021, 05:25 PM   #228
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Originally Posted by slyjoe View Post
That's a great site.

I do have a question on the day 30+ orbit.

The orbit for Webb is roughly circular at the L2 Lagrange point. Since the L2 point doesn't have mass there, the Webb is not orbiting a body in space (like the earth). So, how does it maintain its orbit without constant thruster firing? It must be in constant acceleration, no?
Maybe not constant, but fairly frequently.

I think that's what limits the lifetime of the telescope, its thruster fuel.

The rest of it is solar powered, I think.
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Old 25th December 2021, 05:28 PM   #229
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Originally Posted by slyjoe View Post
That's a great site.

I do have a question on the day 30+ orbit.

The orbit for Webb is roughly circular at the L2 Lagrange point. Since the L2 point doesn't have mass there, the Webb is not orbiting a body in space (like the earth). So, how does it maintain its orbit without constant thruster firing? It must be in constant acceleration, no?
Objects can orbit Lagrange points as if there was a mass there. Here's a link to Wikipedia that makes it clear:

https://en.m.wikipedia.org/wiki/Halo_orbit

Okay, I don't really understand it, but the orbit is unstable so the telescope will have to occasionally use its thrusters to maintain the orbit. As mentioned above, fuel for station keeping will probably be the limiting factor for the life of the telescope. It isn't designed to be repaired or refueled.

Last edited by jadebox; 25th December 2021 at 05:31 PM.
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Old 25th December 2021, 05:51 PM   #230
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Originally Posted by slyjoe View Post
Since the L2 point doesn't have mass there, the Webb is not orbiting a body in space (like the earth).
Webb is orbiting the Sun. The description of it "orbiting" L2 is a fiction. It only appears that way to something at the exact L2 position. It's orbit is a circle about the Sun. That orbit is changing slightly all the time for various complicated reasons but those perturbations cause the appearance of it moving "around L2" when that is just a consequence of it being at the L2 position "on average".


Originally Posted by slyjoe View Post
So, how does it maintain its orbit without constant thruster firing?
Occasional thruster firing is required as others said. However, you thinking this follows from there being "no mass" at L2 is wrong. The L4 and L5 points are stable even though there is no mass there either.

Originally Posted by slyjoe View Post
It must be in constant acceleration, no?
Yes. It's accelerating towards the Sun. All satellites in orbits are constantly accelerating toward whatever they are orbiting. This doesn't have anything to do with being a Lagrange point, stable or not.

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Old 25th December 2021, 05:55 PM   #231
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Originally Posted by RecoveringYuppy View Post
Webb is orbiting the Sun.
it orbits a point which orbits the sun.



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Old 25th December 2021, 05:55 PM   #232
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Originally Posted by slyjoe View Post
That's a great site.

I do have a question on the day 30+ orbit.

The orbit for Webb is roughly circular at the L2 Lagrange point. Since the L2 point doesn't have mass there, the Webb is not orbiting a body in space (like the earth). So, how does it maintain its orbit without constant thruster firing? It must be in constant acceleration, no?
They talked about that on the Launch Pad Astronomy stream.

The thing about the L2 Lagrange point is that it's a bit of a moving target. Its precise position changes depending on the time of year, because the earth's orbit around the sun is not a perfect circle, and the position of the moon also affects it. So there's no single stable point where they can just park it and leave it. They do unfortunately have to use the thrusters from time to time to keep it in the region of relative stability near the lagrange point. The "orbit" is just the way to minimize the amount of thrusting required and maximize the useful life of the telescope.

But I'm not an expert and I'm just trying to paraphrase what I heard someone say.
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Old 25th December 2021, 05:58 PM   #233
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Originally Posted by Puppycow View Post
So there's no single stable point where they can just park it and leave it.
The telescope can't be parked at L2 because then the Earth would block the sun, and since its solar powered, that's bad.

So its orbits L2 only so it can get sun by staying directly out of the way of the Earth.
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Old 25th December 2021, 05:59 PM   #234
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Originally Posted by Mike Helland View Post
it orbits a point which orbits the sun.
Not in the way the word "orbit" is normally used for satellites. I added some explanation to my post while you were posting.
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Old 25th December 2021, 06:02 PM   #235
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Originally Posted by RecoveringYuppy View Post
Not in the way the word "orbit" is normally used for satellites. I added some explanation to my post while you were posting.

..That orbit is changing slightly all the time for various complicated reasons
Its a single simple reason, the solar panels can't be blocked by Earth.
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Old 25th December 2021, 06:05 PM   #236
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Originally Posted by Mike Helland View Post
Its a single simple reason, the solar panels can't be blocked by Earth.
No. The L2 point is beyond the total eclipse point (outside the umbra). There is sunlight at L2. Besides that, I wasn't talking about the reason for the choice of orbit, I was talking about why the halo appears to be an orbit around L2 when it really isn't.

You could read the Wikipedia article.

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Old 25th December 2021, 06:10 PM   #237
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Originally Posted by RecoveringYuppy View Post
No.
Heh. Ok, amigo. Merry Christmas, or Happy Holidays or whatever.

"This orbit (which takes Webb about 6 months to complete once) keeps the telescope out of the shadows of both the Earth and Moon. "

https://webb.nasa.gov/content/about/orbit.html
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Old 25th December 2021, 06:10 PM   #238
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Originally Posted by Mike Helland View Post
The telescope can't be parked at L2 because then the Earth would block the sun, and since its solar powered, that's bad.

So its orbits L2 only so it can get sun by staying directly out of the way of the Earth.
Originally Posted by Mike Helland View Post
Its a single simple reason, the solar panels can't be blocked by Earth.
Huh. If that's true, I wonder why they chose solar panels as a power source. Couldn't they have gone with a nuclear source?
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Old 25th December 2021, 06:13 PM   #239
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Originally Posted by Puppycow View Post
Huh. If that's true, I wonder why they chose solar panels as a power source. Couldn't they have gone with a nuclear source?
NASA is running low on plutonium power sources. They are required for deep space outer solar system stuff, so anything which can get away without them, should.
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Old 25th December 2021, 06:15 PM   #240
slyjoe
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Well, there are other reasons not to park it at L2. It's crowded there.

1 October 2001 – October 2010: Wilkinson Microwave Anisotropy Probe[36]
November 2003 – April 2004: WIND, then it returned to Earth orbit before going to L1 where it still remains
July 2009 – 29 April 2013: Herschel Space Telescope[37]
3 July 2009 – 21 October 2013: Planck Space Observatory
25 August 2011 – April 2012: Chang'e 2,[38][39] from where it travelled to 4179 Toutatis and then into deep space
January 2014: Gaia Space Observatory
2019: Spektr-RG X-Ray Observatory
2021: James Webb Space Telescope uses a halo orbit[40]
2022: Euclid Space Telescope
2024: Nancy Grace Roman Space Telescope (WFIRST) will use a halo orbit
2031: Advanced Telescope for High-Energy Astrophysics (ATHENA) will use a halo orbit

https://en.wikipedia.org/wiki/Lagrange_point
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