James Webb Space Telescope

JWST messages that preceded the no-jinx point were here.

 

Focusing and alignment done. Here is a thumbnail showing the images from the various different cameras, in the same relative positions as they are mounted on the focal plane. For a much more eye-popping hi-res version of this image, see this link and enlarge it to full resolution:

https://blogs.nasa.gov/webb/wp-content/uploads/sites/326/2022/04/webb_img_sharpness.png.



NASA Webb blog: NASA’s Webb In Full Focus, Ready for Instrument Commissioning
CNN: The James Webb Space Telescope is fully aligned and ready to observe the universe

 

MIRI’s Sharper View Hints at New Possibilities for Science

This thumbnail image shows how much improvement Webb provides over the view of the same field from the now-retired SIRTF / Spitzer Space Telescope, Webb's immediate predecessor as an infrared telescope and one of NASA’s Great Observatories. Spitzer was launched in 2003, operated in cold mode until its supply of liquid helium was exhausted in 2009, then two of its instruments were still able to run in 'warm' mode until it was retired two years ago.



Higher resolution here:
https://blogs.nasa.gov/webb/wp-content/uploads/sites/326/2022/05/spitzer_vs_webb_alt.png

or animated GIF, slowly blending from Spitzer to Webb images
https://blogs.nasa.gov/webb/wp-content/uploads/sites/326/2022/05/spitzer_vs_webb_LMC.gif

 

Yeah impressive. I think the "star" artifacts are due to the multi-faceted mirror?

 

It is a mixture of diffraction artifacts from the gaps between mirror facets, the shape of the individual facets, overall mirror shape (both the outer border and the central mirror-less hole), and the three spider legs blocking a bit of light while holding up the secondary mirror.

If the mirror was round, un-faceted, hole-less, and there were no obstructing spider legs, nearly all those star artifacts would disappear, except for a couple faint rings around each central star spot.

Note that in your snippet, at least one other star is bright enough to show a ring, but faint enough to not show the many spikes. The bright central star is so over-exposed that the first ring merges with the central spot.

For more discussion, start here and read the next 5 posts following it:
Hubble in trouble | Page 6 | PriusChat

Post #121 there shows the equivalent diffraction spikes from a Hubble image. Note that its spike structure is much simpler, thanks to Hubble having a single round mirror. Its spikes are from only the secondary mirror support spider vanes.

 

To add a bit more ...

Webb's mirrors segments are now quite well figured and focused and aligned, so very little of that spiky artifact pattern should be from mismatches or misalignments between the mirror segments. Nearly all should be inherent wave action results from mirror shapes and edges, non-reflecting gaps between the mirrors, and support vane shadows . E.g. if you could take a single large perfect mirror, then tape it up with non-reflecting black tape to simulate the mirror gaps and borders and central hole and support vane shadows, you should get almost the same artifact pattern.

Back when the mirrors were individually focused, and images stacked together, but the the mirrors were not yet aligned to the same 'optical height' (wavefront-wise), far more optical energy was thrown out into the spikes, making them much wider and longer than now, and also revealing very many diffraction rings (though mostly as just band segments in the spikes). That is clearly shown in the second image here:
Hubble in trouble | Page 6 | PriusChat

Something I would like to have seen would have been a same-scale comparison of one of the many single-mirror images in the first photo above, alongside the stacked image in the second photo. The properly focused central spot diameter is supposed to be inversely proportional to the mirror diameter. That means the final all-mirrors image should produce a central spot size one-fifth the diameter of the single-mirror spots. If this effect isn't seen in the final stacked but unaligned photo, then it most certainly should show up by the final fully aligned photo (when not similarly super-over-exposed).

In Mendel's snippet, notice that all the mid-brightness stars (not counting the ring around one of them) seem of have exactly the same diameter. This isn't a representation of the stars' apparent size, but is just the Airy disk image diameter of this specific telescope looking at a point (or too small to resolve) source.

Note also that the big bright star (with spikes) has an apparent disk diameter that essentially matches the ring size around the brightest star to its lower left. This is no coincidence. Both should have the same central disk and first ring diameters, but the big spikey star is so over-exposed that its first ring and central disk merge into one (as displayed here for humans, probably not in the raw image sensor data).

The dimmer stars do seem to have smaller diameters, but that is because we are not seeing the whole Airy disk, but just the peak of the center spike. If we could adjust the displayed image brightness and contrast and/or get long enough exposures to show the whole spike, we should see the same size Airy disk as the mid-brightness stars.

 

Here's an oldie that sorta applies.
The Far Side comic strip by Gary Larson from Wednesday, May 11, 2022 | TheFarSide.com

 

The moment many have been waiting for now with a specific date:

NASA’s James Webb Space Telescope, a partnership with ESA (European Space Agency) and the Canadian Space Agency (CSA), will release its first full-color images and spectroscopic data on July 12, 2022. ​

https://www.nasa.gov/feature/goddard/2022/first-images-from-nasa-s-webb-space-telescope-coming-soon

 

I presume to put GAIA telescope here because it is also doing donuts around L2, and has recently dumped a lot of data:

ESA - Gaia overview

New Milky Way Visualizations Show the Dance of Millions of Stars in Incredible Detail

For the masses, these are interesting images to see. For astronomers they reveal much about galaxy and beyond.

I only speculate that some GAIA stars may also be interesting targets for JWST.

 

In this ongoing Instrument Modes Check Out and Commissioning phase, they have now reached 16 out of 17 modes completed. Only one more to go:

 

2 days to go. NASA plans to reveal the pictures at 10:30 a.m. Eastern time on Tuesday. They have selected 5 new images to demonstrate the capabilities of the new telescope.

 

Completed yesterday.

Part of this apparently moved up to 5 p.m. ET today, by Biden at the White House. “Webb’s First Deep Field."

 

Press release:

https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-delivers-deepest-infrared-image-of-universe-yet

Today's high-res deep field (45387 x 4630 pixels), showing loads of Einstein arcs:

https://jwst.nasa.gov/content/webbLaunch/assets/images/firstImages/SMACS0723_nircam-FullRez.jpg

Reduced resolution:

 

Heckuva photo. Actually this is described as a preview with the 'first' image 13 hrs later. I think they are still photoshopping out the Ronulan birds of prey or whatnot.

 

I think the White House desperately wanted some good PR, so managed to finagle an early release of one item on its own stage.

 

While "desperately" seems an editorial flourish, there is no doubt that Executive Branch wants to be part of this rollout. Biden was VP during much of JWST gestation; may count for something. Broadly, when has Executive Branch not wanted to be linked to benefits of Big Science investments? Few have been larger than this one.

But back to astronomy, the five initial targets are pretty juicy at least in terns of wall art. Stephan's Quintet features galaxies a bit too close that are pulling on others' tails. Teaser posted above shows galaxies light distorted by intervening mass during light flight towards earth. They tell similar stories in different ways. Gravity always gets ya - sooner or later.

We knew that locally from sitting under apple trees, but the big G has no scale limitation.

 

Hubble and Webb images compared:





Hubble


Webb


Hubble


Webb




Comparing Webb's First Photos to What Hubble Saw | PetaPixel

 

Nice

 

This pairing clearly shows the difference between optical and infrared bands. The Hubble optical view shows numerous dark dust lanes obscuring the visible light behind. The Webb IR view shows these very same dust lanes glowing from their own warmth.

The PetaPixel article seems to suggest that Webb has higher resolution than Hubble, then makes no mention that they are viewing different wavelength bands. But my understanding is that Webb's resolution is not better the Hubble. They are similar with Hubble still holding an edge. The difference in these pictures is almost entirely from the differing wavelength windows. Webb gets to see through some obscuring dust that blocks visible light from Hubble.