# James Webb Space Telescope general discussion thread **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Tags:** science-math\ **Created:** [December 25, 2021, 1:18pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624 "2021-12-25T13:18:56Z")\ **Posts on this page:** 20\ **Page:** 26
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 22, 2022, 12:13am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/501 "2022-03-22T00:13:04Z")
There are two sources of spiking. The sixfold spiking is due to diffraction in the optics, either from the hexagonal mirrors or from the tripod mount in front of the mirrors (you’ll always get an even number of spikes, so threefold symmetry leads to sixfold symmetry). There’s also a fourfold spiking, that’s in the detector, because oversaturated pixels bleed over into adjacent pixels. This is an image of a single point-source star. Bright point sources are good for calibrating a telescope, but they’re not all that interesting scientifically (at least, not until after you feed them through a spectroscope). The objects that JWST will be imaging as its actual mission will be too diffuse to cause these effects. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [March 22, 2022, 4:10am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/502 "2022-03-22T04:10:23Z")
> [@Chronos](#): > > There’s also a fourfold spiking, that’s in the detector, because oversaturated pixels bleed over into adjacent pixels. I believe the JWST instruments are not subject to this. The NIRCam sensors have a similar design to Hubble’s WFC3 sensor. A comment on the WFC3: [http://guaix.fis.ucm.es/~agpaz/Instrumentacion\_Espacio\_2010/Espacio\_Docs/HST/hst\_c17\_wfc3\_ihb.pdf](http://guaix.fis.ucm.es/~agpaz/Instrumentacion_Espacio_2010/Espacio_Docs/HST/hst_c17_wfc3_ihb.pdf) > Compared to CCD detectors, IR detectors like the one used in the WFC3 IR channel show higher read noise and dark current. Unlike CCDs, however, IR detectors allow the accumulated signal to be read out non-destructively multiple times, without affecting other pixels. The capability to sample the signal multiple times during the integration can be exploited to reduce the effective read-out noise significantly. **IR detectors are also immune to the charge bleeding exhibited by CCDs at high signal levels** ; however, saturation may still be a problem because pixels subject to the highest signal levels show higher dark-current rates (“image persistence”) in subsequent exposures. This also makes sense based on the physical design. The detectors have a separate absorber layer divided into pixels: > **[Infrared Detectors Webb/NASA](https://webb.nasa.gov/content/about/innovations/infrared.html)** > > The James Webb Space Telescope (sometimes called Webb or JWST) is a large infrared telescope with a 6.5-meter primary mirror. Webb is the premier observatory of the next decade, serving thousands of astronomers worldwide. It studies every phase in... Even if a pixel in the absorber layer saturates, it should not bleed into adjacent pixels. The readout sensor is separate and should be able to read the full range of possible voltage levels. That’s in contrast to a CCD where once the charge builds up too much, it has no place to go besides adjacent pixels. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 22, 2022, 11:21pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/503 "2022-03-22T23:21:47Z")
> [@Dr.Strangelove](#): > > I believe the JWST instruments are not subject to this. Then what is causing the horizontal spiking? There’s definitely some of that in that image, though not as much as the sixfold pattern. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [March 23, 2022, 12:43am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/504 "2022-03-23T00:43:40Z")
I believe that’s from the third/top strut. Two of the struts are placed in the same orientation as the edges of the mirror segments. The third strut is not–it’s halfway between: [![](https://i.imgur.com/ytnzcR7.png) ](https://i.imgur.com/ytnzcR7.png) ---
**Author:** ![Bootb](https://avatars.discourse-cdn.com/v4/letter/b/e19b73/32.png) [@Bootb](https://boards.straightdope.com/u/Bootb)\ **Post date:** [March 28, 2022, 4:01am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/505 "2022-03-28T04:01:18Z")
I don’t know how many have seen the latest update. It gives more information on the other instruments on the telescope. [https://blogs.nasa.gov/webb/2022/03/24/webb-continues-multi-instrument-alignment/](https://blogs.nasa.gov/webb/2022/03/24/webb-continues-multi-instrument-alignment/) ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [April 8, 2022, 9:02pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/506 "2022-04-08T21:02:32Z")
Where is Webb website now reporting MIRI at 6K. Makes me feel like shivering, even though spring is sprung here and we’ve got a whopping 291K outside just now. I believe everything is now at final operating temps. > **[Where Is Webb? NASA/Webb](https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric)** > > During Webb's launch, deployment and commissioning, 'WhereIsWebb' tracked Webb's 'flight' to L2 orbit, its state and progress during its deployment and commissioning process, and finally the release of its first images. This process is now complete.... ---
**Author:** ![kwintenstraler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kwintenstraler/32/10698_2.png) [@kwintenstraler](https://boards.straightdope.com/u/kwintenstraler)\ **Post date:** [April 8, 2022, 9:04pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/507 "2022-04-08T21:04:43Z")
Cool! ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [April 8, 2022, 9:35pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/508 "2022-04-08T21:35:30Z")
That went down quickly ! (There are new temp graphs on the site to prove it !) ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 8, 2022, 10:05pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/509 "2022-04-08T22:05:35Z")
> [@kwintenstraler](#): > > Cool! Downright cryogenically frigid! ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [April 28, 2022, 8:29pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/510 "2022-04-28T20:29:30Z")
Ok, 4 months in and ONLY ONE PICTURE ?! Come on NASA guys - you must have some other stuff to share. ---
**Author:** ![kwintenstraler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kwintenstraler/32/10698_2.png) [@kwintenstraler](https://boards.straightdope.com/u/kwintenstraler)\ **Post date:** [April 28, 2022, 8:41pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/511 "2022-04-28T20:41:00Z")
Well… here you have some testing images [![](https://jwst.nasa.gov/content/webbLaunch/assets/images/mirrorAlignment/mirrorAlignmentCompleteFullFieldImage-1400px.jpg) ](https://jwst.nasa.gov/content/webbLaunch/assets/images/mirrorAlignment/mirrorAlignmentCompleteFullFieldImage-1400px.jpg) ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [April 29, 2022, 3:12am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/512 "2022-04-29T03:12:38Z")
> [@pjd](#): > > Ok, 4 months in and ONLY ONE PICTURE ?! > Come on NASA guys - you must have some other stuff to share. It seems they are now ready to start taking “real” pics (by “real” I mean with the telescope fully functioning and doing its thing). That said, it seems it will not be until sometime this summer before we see the first pictures. [https://www.cnn.com/2022/04/28/world/james-webb-space-telescope-alignment-scn/index.html](https://www.cnn.com/2022/04/28/world/james-webb-space-telescope-alignment-scn/index.html) ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [April 29, 2022, 1:56pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/513 "2022-04-29T13:56:54Z")
_ **She’s** _ teasing us. Like an attractive _ **woman** _ who has all the control over us, _ **she’s** _ teasing us. And it’s working. ETA — don’t mean to assume we’re all _ **hetero males** _ here. Please, substitute the appropriate words in bold, italics that fit your situation. 🙂 ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [May 2, 2022, 2:03pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/514 "2022-05-02T14:03:06Z")
There’s still some calibration work on the various instruments to do. ---
**Author:** ![kwintenstraler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kwintenstraler/32/10698_2.png) [@kwintenstraler](https://boards.straightdope.com/u/kwintenstraler)\ **Post date:** [May 11, 2022, 1:02pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/515 "2022-05-11T13:02:13Z")
> **[James Webb telescope reaches 'perfect' alignment ahead of debut science images](https://www.livescience.com/james-webb-telescope-perfectly-aligned)** > > The telescope's first science images drop in July. JWST has reached alignment ahead of schedule according to this article ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [May 20, 2022, 2:09am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/516 "2022-05-20T02:09:34Z")
I’ve just discovered that among the 248 or so approved projects for the JWST will be a search for life on the Trappist-1 system! Trappist-1 was an exciting find a few years ago because it consists of seven planets orbiting close to a cool star, of which three (Trappist-1e, -1f, and -1g) are thought to be in the habitable zone. This made the Trappist-1 system really fascinating. And now the full power of the JWST will be brought to bear on those three planets, through spectroscopic analysis of their atmospheres for signatures of life like water vapour and free oxygen. It’s a long shot, but the first signature of (at least probable) extraterrestrial life could possibly be found soon. [https://www.nasa.gov/feature/goddard/2020/nasa-s-webb-will-seek-atmospheres-around-potentially-habitable-exoplanets](https://www.nasa.gov/feature/goddard/2020/nasa-s-webb-will-seek-atmospheres-around-potentially-habitable-exoplanets) ---
**Author:** ![Bullitt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bullitt/32/5725_2.png) [@Bullitt](https://boards.straightdope.com/u/Bullitt)\ **Post date:** [May 20, 2022, 6:27am UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/517 "2022-05-20T06:27:38Z")
Cool. Class M planets! ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [May 20, 2022, 1:04pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/518 "2022-05-20T13:04:15Z")
… but that Instrument Modes Check Out / Mode Commissioning Tracker hasn’t changed in _weeks_ ! ---
**Author:** ![JKellyMap](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jkellymap/32/15880_2.png) [@JKellyMap](https://boards.straightdope.com/u/JKellyMap)\ **Post date:** [May 20, 2022, 4:08pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/519 "2022-05-20T16:08:51Z")
> [@kwintenstraler](#): > > JWST has reached alignment ahead of schedule according to this article Excellent! ---
**Author:** ![Cardigan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardigan/32/187_2.png) [@Cardigan](https://boards.straightdope.com/u/Cardigan)\ **Post date:** [May 25, 2022, 12:48pm UTC](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624/520 "2022-05-25T12:48:02Z")
Shouldn’t the JWST start officially doing science any day now? [Previous page](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624.md?page=25) [Next page](https://boards.straightdope.com/t/james-webb-space-telescope-general-discussion-thread/956624.md?page=27)