Questions : is Chang’e 2 orbiter still in L2 ? I believe it’s the only one active there. Does it have any chance to take a picture of Webb ?

https://en.wikipedia.org/wiki/List_of_objec...range_points#L2

With regards to Chang'e2 ... I don't know. But if we hear, we should perhaps update the wiki article.

Yes that's part of it with the other considerations explained here:

https://blogs.nasa.gov/webb/2022/01/06/why-...oyment-cameras/

By the way, the first mirror wing deployment is in progress! There is a plan for live NASA TV coverage Jan 8 around 1400 UTC for the second wing.

Amateur telescopes will be able to image JWST (as a dot), given ephemeris and depending upon the reflective properties of the exposed sunshield. In fact, an amateur already did so while it was about 1/6 of the way to L2, and longer exposures will enable this to occur during its main mission. Of course, larger professional telescopes including HST will be able to image it.

But the sunshield will be the only part in sunlight, by design. We are never going to see pictures of it deployed looking elegant.

Good evening,

Excerpts from Wikipedia:

"According to Ouyang Ziyuan at the 16th conference of the Chinese Academy of Sciences, Chang'e 2 left Lagrange Point L2 on 15 April 2012 to fly over asteroid (4179) Toutatis."

"The probe is then placed on a flight path of the asteroid (4179) Toutatis15. The meeting took place on 13 December at 8:30 UTC at a relative speed of 10.73 km/s. Chang'e 2 passes a distance of 3.2 km from the asteroid and manages to take a dozen images of the asteroid with a maximum resolution of 10 meters per pixel."

"Since 2012, Chang'e 2 has left Earth-Moon space. In 2016, Chang'e 2 has reached a distance of 200 million km from Earth. The probe is used to verify the Chinese network tracking capabilities for far space. It could return to the terrestrial environment around 2029."

It's worth adding - the Lagrange points are not.....'points'. The spacecraft at L1, for example....there can be >500,00km between them, as they halo-orbit they way around.

For example, right now it's 468,000km between SOHO and DSCOVR, and 694,000km between DSCOVR and WIND, and 482,00km between WIND and SOHO

Even for something as powerful as HiRISE JWST would be a fraction of a pixel at those distances.

Thanks Doug, I knew it was a halo but didn’t knew it was that large

The left wing of primary mirror segments has been successfully deployed. Right wing deployment should begin next. There's no single moment when we will suddenly say that the risks of a successful JWST mission are all behind us, but things are definitely looking good now.

The telescope is now fully deployed, though latching activities continue.

Congratulations to the team!

NASA Twitter

This is a slowly-unfolding victory taking place. There are still many, many fine-tunings to be made with the actuators that will reorient each mirror segment to fine precision, and that step is crucially important to attaining proper focus. With memories of HST's focus problems, I don't want to count JWST's deployment as complete before this is done, but it certainly seems like the biggest points of failure – certainly by far the largest number of them – have been put behind the mission.

Not really worried about optics or focusing. Each primary segment has 7 degrees of freedom. I'm sure there's enough range to compensate for all sorts of scenarios. Hubble had nowhere near this level of control for focusing. JWST's testing was more integrated too.

Now.. Will the already 10+ years old electronics hold up? Computers/semiconductors, detectors, capacitors..

Chang'e2 is at the Earth-Moon L2 point. The JWST is going to be at the Earth-Sun L2 point. These are completely different locations.

CE-2 is in solar orbit after flying by Toutatis.
CE-5T1 is reportedly at the Earth-Moon L2, like the CE-4 relay satellite
The status of return module of CE-5 is not clear. After spending some time at one of the Earth-Sun Lagrangian points it is now back in lunar orbit or in a distant Earth orbit

Edit: CE-5 has just been recovered by radio-amateurs in lunar orbit https://twitter.com/coastal8049/status/1479619134681800704

For a commemorative photo, why not use Hubble or Keck.

Heidi Hammel addressed this at today's excellent JWST news conference and Q&A. She indicated that ground based images (already being taken by the amateur community for example) would be more likely than using Hubble. This question at 1:08:40 in the video.

https://www.c-span.org/video/?517137-1/jame...iefing&live

She then pivoted the question to joint science between Hubble and JWST. Also a good summary of solar system observations by JWST.

At a distance of 1.5e6 km, the Hubble's ACS instrument gets a resolution of 364 meters/pixel, so JWST would be a dimensionless point.

I hope that the images that JWST will actually take can attract as much enthusiasm as some have for a hypothetical photo of JWST.

Of the Cycle 1 plans, one of the most imaginative campaigns will image the Galileans while they're in Jupiter's shadow for the purpose not of imaging them (they will be ~black in the given wavelengths) but for seeing the silhouettes of them against the background radiation from the galaxy. These two brightness measurements will tell us the brightness of the zodiacal light, which is the reflection of sunlight from dust between Earth and Jupiter, and then the brightness of the galaxy, which will be the brightness of the area around the Galileans minus the brightness of their silhouettes.

Then we have many exoplanet campaigns, many solar system campaigns (of course, mainly outer solar system and small body targets) and many observations of black holes, stellar objects, and objects of cosmological interest.

Out of curiosity does the public know the actual first target planned?

I can't seem to find much about the first public photos planned.

An analyst who put their mind to it might be able to make some guesses, but it's not possible to know the exact schedule of observations until it's known when commissioning will end and science observations begin. Some of the planned observations are time-limited and if, say, the start of science were delayed a week, it might mean that one observation would have to be shifted from, eg, August 2022 to August 2023.

Basically, targets on the ecliptic are limited to about 100 days of accessibility each year. Targets far from the ecliptic are limited little or zero. Solar system targets have their own complex timing constraints. And exoplanet transits have their own complex periodicity (particularly if the period is relatively longer). So it's impossible to fully schedule the first year until the precise start of science observations is known.

Very intriguing idea - can you point to any details about this?

It sounds really hard. The zodiacal light away from the sun is extremely faint - even the Gegenschein you'd be looking through when Jupiter was near opposition is very faint. So any light scattered onto the eclipsed moons could easily be important. Eg, you'd expect some light scattered around the limb of Jupiter. This is analagous to the orange glow of our moon during total lunar eclipse, but probably fainter for a deeper Galilean eclipse. Also light scattered from the other Galileans, and even illumination from the inner solar system zodiacal light.

Jupiter's well off the Galactic plane for the next while, so the background would also be extremely faint.

Given all that I could imagine the eclipsed discs to be brighter than the background galaxy glow. And all of this imaging while crazy-bright Jupiter is nearby!

Here is the proposal. As you note, Jupiter is well off the galactic plane; the study is looking at extra-galactic background luminosity, and must be made before Jupiter returns to the galactic plane.

If the signal is strong enough, the complicating sources of noise can be accounted for. Eg, light from Jupiter will occur above and below the moon's silhouette as well. The thermal contribution of each moon should be a known quantity. Europa, Ganymede, and Callisto will all be observed.

https://www.stsci.edu/jwst/phase2-public/2134.pdf

Yes the background Milky Way galaxy glow is something that would be interesting to map around different galactic lat/lons. Even ground based deep imaging (both professional and amateur communities) can show faint galactic cirrus when looking away from the galactic plane. A related key question is what is the brightness of extragalactic glow (as noted in the post/proposal just above). This would ostensibly be from unresolved galaxies that wouldn't be seen in something like the Hubble Deep Field. Can this proposal really discriminate between galactic cirrus (DGL) and extragalactic background glow (EBL)? They are both of comparable brightness.

Thanks for that.

They do discuss (though non-quantitatively) stray light from Jupiter in the optical system, but they don't mention any of the sources of light that will illuminate the eclipsed discs of the moons. With Jupiter subtending only a few degrees from the outer Galileans, solar corona and zodiacal light would seem to be potentially important.

New horizons made some interesting observations from well outside the zodiacal glow, though they were limited by the instrumentation which wasn't ideal for that application:

https://arxiv.org/abs/2011.03052

And in a somewhat unrelated thought, one wonders if Webb will be able to see to the point where the Opaque Universe become the Clear Universe.

--Bill

Was wondering to what extent Jupiter being relatively hot in the infrared could impart 'backshine' brightening the moon's silhouette, but the proposal seems to suggest otherwise:

"...However, Jupiter is dark at F140M owing to the methane absorption in the Jovian atmosphere, thus stray light from Jupiter is also reduced..."

It cannot. The light from that event, which is called recombination, is at z = 1100. I.e., it's been redshifted 1100-fold,
from near infrared at the time of recombination to microwave now. That's what the cosmic microwave background is.

So this will indeed take us to the edge of the optical Universe.
Next step: VLB radio space telescopes to go microwave and beyond.

--Bill

For context, Planck has already mapped the microwave background, seeing back further than JWST will see – but at very low resolution.

Spitzer imaged at IR wavelengths comparable to JWST – but at less resolution and with far, far less light gathering.

HST images at about the same resolution as JWST – but different wavelengths.

JWST isn't so much extending capabilities in some single dimension that hasn't been investigated before, but in a combination of dimensions, a corner of the space so to speak, that will be entirely new.

Yeah, Planck (and others) have mapped the cosmic microwave background (CMB) at much lower resolution than JWST is capable of, but there very likely isn't much to see in the CMB at JWST resolutions, since the CMB was emitted well before the first stars and galaxies formed, when the Universe was extremely smooth.

JWST should, for the first time, be able to see back to the first stars, which is one of its main goals. UV light from those stars reionized the gas, which was neutral and transparent since recombination when the CMB was emitted. The time of reionization is considered one of the half dozen or so parameters that describe the Universe in bulk, so this will be a big thing for cosmology.

An individual mirror segment deployment tracker is on display! (that's enough detail for anyone!)

https://webb.nasa.gov/content/webbLaunch/wh...ml?units=metric

They are cranking on moving the mirrors. Down to 2.0 mm on all mirrors except A3 and A6 which still have 12.3mm to go. Somehow A3 and A6 get measured differently and are moved after all the others. The mirrors are cooling down, now at -206C on way to -233C. Webb is 93% the way to L2 and the insertion burn is in about 5 days.
Go Webb!!

Now down to 0.0mm for all segments but A3 and A6, which are down to -10.0mm.

Really motoring!

Click to view attachment

A3 & A6 are a bit wonky at calibration, so IIRC they got calibration data on all the other mirrors to help guestimate / constrain the measurements.

IIRC, stress/strain gauges used to measure alignment didn't cooperate after assembly, so they're working out correct mirror position based on a proxy measurement like of total current through the adjustment motors?

So AFAIK, (somebody please correct this because I'm sure it's wrong in one or many ways) they measured mirror displacement and total motor current to be able to figure out mirror displacement based on net current,
after the direct measurement mechanism on A3 & A6 went wonky.

Thanks for presenting your understanding of what makes A3 and A6 different--very likely mostly correct..
The movement of the mirrors was substantially faster than 1mm/day--so moving faster than grass grows by 2-4x.

All segments now at 0.0mm:

Click to view attachment

Do the motors that performed the mirror extension out of launch position also adjust positioning and tilting?

That's my understanding.

JWST has entered its mission orbit around L2! The next steps are to focus the mirrors, cool down passively, and prepare for science to begin.

Such exciting news! This whole journey has had just the right amount of drama. And by that, I mean none. Well done to that team. I can't wait until we see the first image in several months!

Webb first image (and a selfie to boot!).

A first baby-step of many!!

--Bill

Even more detail on this tracking page has been added:
https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html
Now including instrument temperatures, mirror steps too.

More forward progress:

Webb Team Brings 18 Dots of Starlight into Hexagonal Formation

https://blogs.nasa.gov/webb/2022/02/18/webb...onal-formation/

NASA held an informative press conference today to announce completion of alignment of the JWST’s primary mirror and the capture of a fully-focused image. I watched it on a live stream and since then haven’t been able to find an archived copy. (My track record for finding archived copies of NASA and JPL press conferences is remarkably poor.)

Here’s an early press account, from New Scientist. https://www.newscientist.com/article/231264...rest-image-yet/

Still can't find a youtube link to today's press conference, but here's a twitter link to the video:

https://twitter.com/NASA/status/1504125485969772544

As Tom reported, here is the first aligned and collimated image from Webb. Note the many distant galaxies around the reference star!

https://amp-abc-net-au.cdn.ampproject.org/v...age%2F100916480

--Bill

The MIRI is now actively being cooled. For the past week it's temperature has dropped about 5 degrees kelvin/day and is now at 53 K on its way to 6 K.

April 28: "...Alignment of NASA’s James Webb Space Telescope is now complete (...) Upon completing the seventh and final stage of telescope alignment (...) Webb is ready to move forward into its next and final series of preparations, known as science instrument commissioning. This process will take about two months before scientific operations begin in the summer..."

https://blogs.nasa.gov/webb/2022/04/28/nasa...-commissioning/

"NASA will hold a media teleconference at 11 a.m. EDT on Monday, May 9, to discuss progress toward preparing the James Webb Space Telescope for science operations. The agency will livestream audio of the teleconference on its website": https://www.nasa.gov/live

https://www.nasa.gov/press-release/nasa-to-...nstrument-setup