Hubble in trouble

posto duplicado

 

Here is a description of current capabilities of radio astronomy:

Technology | Event Horizon Telescope

Towards the end it considers imaging the black hole central to our galaxy. Goal is 10 micro arc seconds.

Optical astronomy is 3 orders of magnitude coarser than that and that gap may persist. I wish we had a real astronomer here to teach about what work at what wavelengths might reveal what.

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If any aspect of earth human technology draws attention from other galactic civilizations (if they do exist), it will be this. Not cars and not medicine. Sorry, guys.

 

On a tangentially related note ...

Physicist (and astronomer) Steven Weinberg passed away Friday, at age 88:

With Steven Weinberg’s death, physics loses a titan | Science News

Steven Weinberg - Wikipedia

 

JWST is now intended to launch Dec 18. Very long delayed and up budgeted. It will bring Hubble-scale resolution to infrared, and is larger to collect more photons. Photons are not so abundant in infrared, especially from exo planets, that optimists hope to see with it. Along with galaxies very far away a long time ago. Cue theme music.

It is intended to survive rigors of launch, unfold, and take its station more than a million km from earth. Perhaps during its service life it will become possible to go there and resupply fuel required for 'station keeping'.

Our earlier discussion here about angular resolution (could be in milli arc seconds) sent me back to possibly accurate math. Looking out from earth (or JWST's Lagrange point), the whole sky (observable universe) can be seen as a beach ball with observer in the center. If a 'pixel' spans 40 milli arc seconds, there are about 2 X 10^15 pixels to observe. That is a very large number, and target priorities will be for astronomers to contest after it comes alive. Does one JWST image cover 2 million pixels? Probably something like that, which still leaves a billion decisions about where to look. It promises to be quite an adventure.

Finally it will only be from good luck during its energetic departure, and different luck later, for JWST to approach Hubble's 3-decade run.

A plucky not-yet-interstellar civilization did this, even with only fire to push it out! Other interstellar civilizations might notice in a benevolent way. Or have they already? Bwa ha ha.

 

It looks like 10 simultaneous 4.1 Mpix sensors, for a total of 41 Mpix: https://www.stsci.edu/jwst/instrumentation/imaging-modes


"MIRI provides broad-band imaging at the longest wavelengths in nine filters from 5.6 to 25.5 μm. MIRI imaging has a field of view of 74”x113”, with a pixel scale of 0.11".


NIRCam imaging has two parallel modules, each with a field of view of 2.2’x2.2’, and separated by a ~44” gap. Within each module, the light is split by a dichroic and sent to a short-wavelength (SW, 0.6-2.3 μm) and a long-wavelength (LW, 2.4-5 μm) channel. Each SW module is split into 4 separate detectors. In total, NIRCam images simultaneously with ten 2040x2040 detectors, for a total of more than 41 million pixels. The short-wavelength channel has a pixel scale of ~0.031", which Nyquist-samples a point source at 2 μm. The long-wavelength channel has a pixel scale of ~0.063". Each channel has a comprehensive selection of wide-, medium-, and narrow-band filters.


NIRISS is capable of imaging from 0.8 to 5 μm with a field of view of 2.2’x2.2’. It uses a spare filter set from NIRCam and has a pixel scale of 0.065" per pixel, which matches the sampling of the NIRCam long-wavelength channel. In general, NIRCam is the camera of choice for near-infrared imaging with JWST, since it has twice the field of view of NIRISS and obtains SW and LW images simultaneously. However, used in parallel with NIRCam, NIRISS imaging can increase the field-of-view and efficiency of near-infrared imaging."

 

This page shows the relative positions of these and other sensors on the focal plane:
JWST Imaging - JWST User Documentation

 

More pregame show for JWST

James Webb's 30 Days of Terror - Universe Today

 

I’m more worried about the first 30 minutes….but yeah.

I take their point.
Pleasantly surprised that they haven’t had to change JWST’s initials…….yet.

 

JWST scheduled for Dec 22, so here is another description and comparison with Hubble:

https://www.quantamagazine.org/why-nasas-james-webb-space-telescope-matters-so-much-20211203/

I am glad to (finally) read that red shift Doppler effect stretches starlight wavelengths by as much as 20 times. That is some high-speed away going ...

 

The greatest red shift of any stars should be a direct function of the Universe's age when the first stars formed. But I haven't mentally absorbed all the pieces of cosmological (vs just speed, they are different) red shift, so don't have a proper translation between z / speed / age / distance.

The cosmic microwave background radiation, currently at 2.7K, would have been white light when it was emitted, so it has a red shift on the order of 1000.

 

JWST launch delay until Dec 25

Launch of Webb telescope delayed to Christmas morning – Spaceflight Now

Which also says launch window is only 32 minutes 'wide'. It perplexes me that there is only 1/48 of an earth rotation to shoot at L2. Fuel supply limitation? Dun no.

JWST should fairly have its own thread here. Let us start that after its outgoing looks nominal. Don't jinx the thing.

 

I stumbled upon a "launch window trade analysis" for mid 2018 through 2019. Presumably a current version would have very many similarities:

https://ntrs.nasa.gov/api/citations/20160001318/downloads/20160001318.pdf

I haven't yet looked close enough to decide if I might ever be able to sufficiently understand it. At first glance, launch windows vary from about 5 minutes to just under 2 hours.

"The stray light requirement protects the JWST instruments from solar, lunar and Earth stray light."

 

Following post#70 this

What do redshifts tell astronomers? | Astronomy Essentials | EarthSky.

Teaches more than I know

Except for the other tiny extreme of spectral shifts. Way out yonder, spectra are reddened a lot. In Milky Way galaxy local, stellar spectra shifts from big planets orbiting are now detectable at about 10 meters per second star wobble. It requires $uper-accurate $pectro$copy device$ that remain far beyond launchable.

So, earth-sited telescopes will add to list of exoplanets in this way. JWST in its spare time from deep-space looking might reveal something about exoplanet atmospheres

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I hope readers here realize that astronomy during your lives has done so much more to change sky looking into sky understanding, than ever before. I mean, dang.

 

It's amazing all that we have learned in a short time. I just wonder...will we ever determine the origin of the universe or is it something way beyond our ability to ever know?

 

Probably not “we.”

HOWEVER (comma!)
I have high hopes for those that follow……

 

Naaah.
I don't spend much time worrying about things that I cannot control, especially if they are statistically very, very VERY unlikely.

 

If not noted here before, USD$10 billion to make JWST does not include cost of the Ariane 5 launch; another 0.1 at least. It is, surely, the most expensive single (uninhabited) space exploration by the home team. In less than 9 hours that adventure begins.

It is Christmas eve for many readers and as such they had better be doing something other than reading here! For those in the 'doing' loop, whose this-year Christmas has been altered uniquely, I can only wish the best.

Dear Santa, please make this thing work. If it does not, a very long time will pass before a replacement would be built.

 

Launch success and no problems have been reported with the unfoldings so far. The most active play-by-play site may be:

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

although it does not appear to mention trajectory 'burns' on the way to L2. Several other satellites are already looping around L2 but I have not seen a complete list. Loops seem to be on the scale of 1 kilometer.

The TL;DR is it will take about a month to arrive, 5 more months to get primary mirror(s) aligned and cold, and then the photo ops begin.