Astronomy and Space

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Pishwish
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Re: Astronomy and Space

Post by Pishwish » Tue Jan 18, 2022 4:08 am

So I was reading a NASASpaceflight thread about the possible atmospheric pollution caused by SpaceX's Starlink constellation. I had seen claims before about satellite burnup causing harm but I didn't really think they were credible, given the amount of meteor mass added to the atmosphere every year. After looking at a few frustratingly vague articles, I couldn't help but feel that there is some motivated reasoning by people hostile to the idea of megaconstellations. This sort of thing: paper by Boley and Byers
Black carbon produced by kerosene-fueled rockets such as SpaceX’s Falcon 9 and alumina particles produced by solid-fueled rockets lead to instantaneous radiative forcing. Modelling of the cumulative effect of emissions from 1000 annual launches of hydrocarbon-fuelled rockets found that, after one decade, the black carbon would result in radiative forcing comparable to that resulting from sub-sonic aviation. Although 1000 launches annually is 10 times the current rate, the construction and renewal of multiple mega-constellations will require dramatic increases in launches. Current launches likely cause non-negligible radiative forcing already
(The modelling (by Ross et al.) was an old paper on the potential impact of suborbital launches using hybrid engines.)

This 2018 Ross and Veda paper on rocket emissions seems to suggest that, basically, nobody knows what effect the launch industry has on the upper atmosphere because there isn't enough data. The main takeaway seems to be that alumina (produced by solid rockets but also by re-entering satellites) and black carbon (produced by kerosene rockets) aerosols cool the Earth's surface but heat up the stratosphere. Ozone depletion is apparently increased by this heating and by the surface area provided by the alumina, but the extent of the depletion is difficult to calculate[*]. Although a previous paper by Ross and Sheaffer claims that instantaneous(?) radiative forcing by BC and alumina are positive, the 2018 paper does note that the forcing is negative (although "negative" is missing from this sentence in the conclusion):
Rocket emissions, though they deplete ozone and cause climate forcing, so far have not been regulated..

Was the earlier finding wrong, or am I not understanding the significance of instantaneous radiative forcing?

The 2018 paper also says
Methane fueled engines can be expected to emit, uniquely, potentially significant amounts of hydrogen oxides (HOx) into the stratosphere.
Does this mean peroxides or weird upper atmosphere radicals?

Don't get me wrong, the lack of data is troubling (a quick readup of ozone depletion indicates that ozone in the lower stratosphere is declining and we have no idea why) and the possible changes to atmospheric chemistry brought about by megaconstellations should be studied.

* and I can't read the sources.

P.S. Everyday astronaut does have a post on this subject, I found it after I wrote this.

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dyqik
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Re: Astronomy and Space

Post by dyqik » Tue Jan 18, 2022 5:41 pm

I'd assume both for the HOx products. Upper atmosphere chemistry gets a bit funky with the high UV flux (see ozone layer depletion, etc.)

Al Capone Junior
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Re: Astronomy and Space

Post by Al Capone Junior » Wed Feb 02, 2022 2:48 am

Every day astronaut is a cool channel.

Also scott manley

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Grumble
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Re: Astronomy and Space

Post by Grumble » Wed Feb 02, 2022 10:02 pm

Black hole found, wandering around the Milky Way
https://arxiv.org/abs/2201.13296
A bit churlish

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Aitch
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Re: Astronomy and Space

Post by Aitch » Sat Feb 05, 2022 7:16 pm

What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
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basementer
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Re: Astronomy and Space

Post by basementer » Sat Feb 05, 2022 7:24 pm

Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
So did I. Did yours include a "dark, serpent-shaped structure" by any chance?
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Aitch
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Re: Astronomy and Space

Post by Aitch » Sat Feb 05, 2022 8:52 pm

basementer wrote:
Sat Feb 05, 2022 7:24 pm
Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
So did I. Did yours include a "dark, serpent-shaped structure" by any chance?
I got "Two Red Spots" - "...a second "red spot" (lower left) that emerged alongside the bigger and more famous Great Red Spot (right)..." Actually, the Great Red Spot looks like a dodgy egg yolk, floating in a cream based pudding. :shock:
Some people call me strange.
I prefer unconventional.
But I'm willing to compromise and accept eccentric
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dyqik
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Re: Astronomy and Space

Post by dyqik » Sat Feb 05, 2022 8:54 pm

Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
Billions and billions of stars.

(It was doing the Hubble Deep Field observations)

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Re: Astronomy and Space

Post by monkey » Sat Feb 05, 2022 9:47 pm

dyqik wrote:
Sat Feb 05, 2022 8:54 pm
Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
Billions and billions of stars.

(It was doing the Hubble Deep Field observations)
Sames. Pretty though.

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Re: Astronomy and Space

Post by Martin_B » Sun Feb 06, 2022 12:30 am

Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
Star Clusters in the Tarantula Nebula, which sounds like an AI generated Doctor Who episode.
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dyqik
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Re: Astronomy and Space

Post by dyqik » Sun Feb 06, 2022 1:11 am

Martin_B wrote:
Sun Feb 06, 2022 12:30 am
Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
Star Clusters in the Tarantula Nebula, which sounds like an AI generated Doctor Who episode.
Screenshot_20220205-201200.png
Screenshot_20220205-201200.png (341.81 KiB) Viewed 1477 times
Bit dull. But could be combined with:
Screenshot_20220205-201307.png
Screenshot_20220205-201307.png (298.5 KiB) Viewed 1476 times

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Re: Astronomy and Space

Post by Gfamily » Sun Feb 06, 2022 1:23 am

For that second one, it's just as well that tarantulas don't do metamorphosis - because the junior phases would literally be instars
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
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Re: Astronomy and Space

Post by Gfamily » Fri Feb 11, 2022 4:24 pm

The JWST team has released the initial alignment mosaic, showing the 18 individual element images
FLU-b-jXoAI_wMI.jpeg
FLU-b-jXoAI_wMI.jpeg (76.21 KiB) Viewed 1408 times
And a selfie as well, it's now the insta' era...
FLU_NS0WYAQHwz_.jpeg
FLU_NS0WYAQHwz_.jpeg (117.45 KiB) Viewed 1408 times
Illuminated by starlight.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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Re: Astronomy and Space

Post by JQH » Sat Feb 12, 2022 3:25 pm

Ghost Head Nebula
And remember that if you botch the exit, the carnival of reaction may be coming to a town near you.

Fintan O'Toole

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Gfamily
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Re: Astronomy and Space

Post by Gfamily » Tue Mar 01, 2022 12:00 am

This website shows the realtime position of various satellite constellations.

Fascinating how different the locations of GPS satellites is compared to satellite internet webs like Starling and OneWeb

https://satellitemap.space/?constellation=GPS
gps constellation.jpg
gps constellation.jpg (56.31 KiB) Viewed 1252 times
https://satellitemap.space/?constellation=starlink
starlink constellation.jpg
starlink constellation.jpg (45.12 KiB) Viewed 1252 times
Obvious when you think of it (internet needs them close to the surface so that latency is reduced), but the difference is graphic when shown.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!

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Brightonian
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Re: Astronomy and Space

Post by Brightonian » Sun Mar 13, 2022 8:27 pm

Someone's told me the Northern Lights could be visible tonight. Unfortunately I'm too far south at the moment. https://www.manchestereveningnews.co.uk ... d-23374065

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Re: Astronomy and Space

Post by IvanV » Mon Mar 14, 2022 1:19 pm

Brightonian wrote:
Sun Mar 13, 2022 8:27 pm
Someone's told me the Northern Lights could be visible tonight. Unfortunately I'm too far south at the moment. https://www.manchestereveningnews.co.uk ... d-23374065
Apparently only as far south as Cumbria. Nice photos from Scotland - BBC

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Re: Astronomy and Space

Post by Ben B » Tue Mar 15, 2022 1:26 pm

Aitch wrote:
Sat Feb 05, 2022 7:16 pm
What Did Hubble See on Your Birthday?

Check out this page to find out.

I got a nice pic of (part of ) Jupiter. :)
Very cool.
Image
The first ten million years were the worst.
And the second ten million, they were the worst too.

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Gfamily
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Re: Astronomy and Space

Post by Gfamily » Thu Mar 17, 2022 5:17 pm

A 35 minute Alignment image showing not only the alignment star, but also a host of background galaxies

The gif shows 4 seconds of the released image, and a levels shift to bring out more background detail (my gif)
JWST Alignment Image.gif
JWST Alignment Image.gif (443.61 KiB) Viewed 1018 times
NB, this represents 1 alignment result for 1 of the sensors available, there are months ahead to refine the alignment for the other imaging and spectroscopic devices.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!

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Grumble
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Re: Astronomy and Space

Post by Grumble » Thu Mar 17, 2022 7:16 pm

Gfamily wrote:
Thu Mar 17, 2022 5:17 pm
A 35 minute Alignment image showing not only the alignment star, but also a host of background galaxies

The gif shows 4 seconds of the released image, and a levels shift to bring out more background detail (my gif)

JWST Alignment Image.gif

NB, this represents 1 alignment result for 1 of the sensors available, there are months ahead to refine the alignment for the other imaging and spectroscopic devices.
Presumably they’ve chosen to align the mirror in the most accurate way they can, are the other alignments more to do with the instruments?
A bit churlish

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Re: Astronomy and Space

Post by monkey » Thu Mar 17, 2022 7:41 pm

Grumble wrote:
Thu Mar 17, 2022 7:16 pm
Gfamily wrote:
Thu Mar 17, 2022 5:17 pm
A 35 minute Alignment image showing not only the alignment star, but also a host of background galaxies

The gif shows 4 seconds of the released image, and a levels shift to bring out more background detail (my gif)

JWST Alignment Image.gif

NB, this represents 1 alignment result for 1 of the sensors available, there are months ahead to refine the alignment for the other imaging and spectroscopic devices.
Presumably they’ve chosen to align the mirror in the most accurate way they can, are the other alignments more to do with the instruments?
IRC, They've aligned it as well as they can to the main instrument (the NIR camera) at the centre of the field of view. The next step is to align it so it is optimised across the whole field for all instruments. There's still more fine tuning of the primary mirror to do.


ETA: I bet Dyqik knows more detail than me.

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Re: Astronomy and Space

Post by Gfamily » Thu Mar 17, 2022 8:13 pm

Grumble wrote:
Thu Mar 17, 2022 7:16 pm
Gfamily wrote:
Thu Mar 17, 2022 5:17 pm
A 35 minute Alignment image showing not only the alignment star, but also a host of background galaxies

The gif shows 4 seconds of the released image, and a levels shift to bring out more background detail (my gif)

JWST Alignment Image.gif

NB, this represents 1 alignment result for 1 of the sensors available, there are months ahead to refine the alignment for the other imaging and spectroscopic devices.
Presumably they’ve chosen to align the mirror in the most accurate way they can, are the other alignments more to do with the instruments?
It's not clear, but as far as I can interpret from some of the descriptions, it's as though there are 4 dimensions to the alignment.

This image represents the basic alignment in 3D, which gives a good image on a flat (or gently curved) image plane.

However, AIUI the next phase is to perform 20 iterations of waveform adjustment, which involves tweaking pairs of mirrors at a time to get an even better alignment (I assume) for the other instruments.

The trouble is, I don't know what they mean. It's like knowing a phrase in a foreign language without really understanding it. I think I have a rough idea, but can't be sure.

If someone can provide a good translation, I'd be grateful.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!

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Re: Astronomy and Space

Post by monkey » Thu Mar 17, 2022 11:02 pm

Gfamily wrote:
Thu Mar 17, 2022 8:13 pm
Grumble wrote:
Thu Mar 17, 2022 7:16 pm
Gfamily wrote:
Thu Mar 17, 2022 5:17 pm
A 35 minute Alignment image showing not only the alignment star, but also a host of background galaxies

The gif shows 4 seconds of the released image, and a levels shift to bring out more background detail (my gif)

JWST Alignment Image.gif

NB, this represents 1 alignment result for 1 of the sensors available, there are months ahead to refine the alignment for the other imaging and spectroscopic devices.
Presumably they’ve chosen to align the mirror in the most accurate way they can, are the other alignments more to do with the instruments?
It's not clear, but as far as I can interpret from some of the descriptions, it's as though there are 4 dimensions to the alignment.

This image represents the basic alignment in 3D, which gives a good image on a flat (or gently curved) image plane.

However, AIUI the next phase is to perform 20 iterations of waveform adjustment, which involves tweaking pairs of mirrors at a time to get an even better alignment (I assume) for the other instruments.

The trouble is, I don't know what they mean. It's like knowing a phrase in a foreign language without really understanding it. I think I have a rough idea, but can't be sure.

If someone can provide a good translation, I'd be grateful.
I'll have a go!

They got all the mirrors pointing the right way using the selfie. This gives you a pretty good image, but it's not aberration* free, so it could be better. Aberrations cause the point spread function to be less than perfect, or if you like simple terms, make your focused spot go all smeary. This lowers image resolution and brightness.

The aberrations come from the wavefronts** from each segment arriving at the focus with different phases. To adjust the phase from each segment, they move them in and out very small amounts (because wavelength is small) till it's correct. e.g. If the light from one segment is arriving at the focus with advanced phase (too soon), you move the mirror outwards, so it gets there a little later and in phase. Positioning is done on a subwavelegnth scale. This is similar to adaptive optics, what you sometimes get in ground based telescopes***. The difference being on the ground they can do a wavefront measurement and correction on the fly. JWT can't do this measurement, so they use a complicated algorithm to optimise the image ). They will only have to do this once (if everything stays still), unlike the ground based AO, where the atmosphere keeps wobbling about and messing things up and you have to correct continuously. This is the step they have just completed.

As I said in another post, they have only corrected for the centre of the field of view (for one instrument). They will have a very nice image in this one spot, but as some aberations are dependent on the angle away from the optical axis, it might not be good near the edges, for example. The next step is to optimise the whole field, again by moving the mirrors in and out, but now they will sacrifice some of the image quality at the centre to improve it over the whole field. Part of this is making sure it's good in all the instruments, I believe they have an algorithm to decide what the best mirror position is for this. Like the field correction, they may sacrifice quality in one instrument, to improve in another.


*Aberrations are stuff like defocus and astigmatism, like what glasses correct, but much they go into higher orders than that, they are normally characterised by the Zernike polynomials - wiki clicky.

** The wavefront is an imaginary line that joins up all the points of a wave that have the same phase.

***And eye imaging, microscopy, and high powered lasers - wiki clicky.

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Re: Astronomy and Space

Post by Grumble » Thu Mar 17, 2022 11:10 pm

monkey wrote:
Thu Mar 17, 2022 11:02 pm
Gfamily wrote:
Grumble wrote:

Presumably they’ve chosen to align the mirror in the most accurate way they can, are the other alignments more to do with the instruments?
It's not clear, but as far as I can interpret from some of the descriptions, it's as though there are 4 dimensions to the alignment.

This image represents the basic alignment in 3D, which gives a good image on a flat (or gently curved) image plane.

However, AIUI the next phase is to perform 20 iterations of waveform adjustment, which involves tweaking pairs of mirrors at a time to get an even better alignment (I assume) for the other instruments.

The trouble is, I don't know what they mean. It's like knowing a phrase in a foreign language without really understanding it. I think I have a rough idea, but can't be sure.

If someone can provide a good translation, I'd be grateful.
I'll have a go!

They got all the mirrors pointing the right way using the selfie. This gives you a pretty good image, but it's not aberration* free, so it could be better. Aberrations cause the point spread function to be less than perfect, or if you like simple terms, make your focused spot go all smeary. This lowers image resolution and brightness.

The aberrations come from the wavefronts** from each segment arriving at the focus with different phases. To adjust the phase from each segment, they move them in and out very small amounts (because wavelength is small) till it's correct. e.g. If the light from one segment is arriving at the focus with advanced phase (too soon), you move the mirror outwards, so it gets there a little later and in phase. Positioning is done on a subwavelegnth scale. This is similar to adaptive optics, what you sometimes get in ground based telescopes***. The difference being on the ground they can do a wavefront measurement and correction on the fly. JWT can't do this measurement, so they use a complicated algorithm to optimise the image ). They will only have to do this once (if everything stays still), unlike the ground based AO, where the atmosphere keeps wobbling about and messing things up and you have to correct continuously. This is the step they have just completed.

As I said in another post, they have only corrected for the centre of the field of view (for one instrument). They will have a very nice image in this one spot, but as some aberations are dependent on the angle away from the optical axis, it might not be good near the edges, for example. The next step is to optimise the whole field, again by moving the mirrors in and out, but now they will sacrifice some of the image quality at the centre to improve it over the whole field. Part of this is making sure it's good in all the instruments, I believe they have an algorithm to decide what the best mirror position is for this. Like the field correction, they may sacrifice quality in one instrument, to improve in another.


*Aberrations are stuff like defocus and astigmatism, like what glasses correct, but much they go into higher orders than that, they are normally characterised by the Zernike polynomials - wiki clicky.

** The wavefront is an imaginary line that joins up all the points of a wave that have the same phase.

***And eye imaging, microscopy, and high powered lasers - wiki clicky.
Thanks monkey. So to give the absolute lies to children version that numpties like me can understand, it may be worth sacrificing some of the ultimate sharpness at the central point in order to get a better overall image (and the best average for all the instruments)?
A bit churlish

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Re: Astronomy and Space

Post by Gfamily » Thu Mar 17, 2022 11:38 pm

monkey wrote:
Thu Mar 17, 2022 11:02 pm
I'll have a go!
ditto, appreciated!
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!

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