Image JWST: Amateur Astronomy Success?

[sophiecentaur]

TL;DR Summary

Has there been any success?

JWST is only four times as far away as the Moon and its sunshield is more than 15m across. Too small to resolve it but it's very well lit and it is against a pretty dark background on occasions.
Its position is 'well known and there are some pretty big light bucket amateur scopes around. Has anyone managed to image it yet?

 

[DaveC426913]

Looks like it's supposed to be ~ mag 13.7.

 

[sophiecentaur]

Cheers. You are a star!

 

[Orodruin]

You are a star!

But what magnitude? Can he be photographed?

 

[TeethWhitener]

Looks like it's supposed to be ~ mag 13.7.

Out of curiosity, where did you find this? I found a SE thread claiming magnitude 15-16 range:
https://astronomy.stackexchange.com...es-webb-space-telescope-be-visible-from-earth

 

[DaveC426913]

Out of curiosity, where did you find this? I found a SE thread claiming magnitude 15-16 range:
https://astronomy.stackexchange.com...es-webb-space-telescope-be-visible-from-earth

Dang it. I was afraid someone would ask. I read it but didn't save the page.

 

[hutchphd]

Lets do some rough calculation. From Nasa
Webb has a 5-layer, tennis court-sized sunshield that acts like a parasol providing shade. [Actual dimensions: 21.197 m x 14.162 m (69.5 ft x 46.5 ft)]

So best case it is 300 m² mirror at 1.5 million km .
The sun subtends half a degree = 5x10^-6steradian.
The mirror subtends (3/2.25)x10^-16steradian
The magnitude of the sun is -26

Absolute best case if the shield is a perfect mirror and points back at the sun
$$\frac {I_{Webb}} {I_{sun}}=(3/11.25)x10^{-10} \approx 10^{-10.5}$$ So absolute best case $$ mag_{Webb}=mag_{sun}+(2.5)(10.5) \approx 0 $$

Seems high but that is clearly a generous estimate.

 

[sophiecentaur]

But what magnitude? Can he be photographed?

Could he sit still for long enough, though? Back to early Dagerrotype portraits.

 

[sophiecentaur]

Alternatively (?) If the Sun is reflected straight back to Earth then that's the equivalent of a hole in a screen that's the radius of the telescope sunshade. Ratio of areas is 10e-16, which is a relative magnitude of about 35(??) so that could mean a magnitude of 35-26 = 9
That would be if the sunscreen were a flat reflector and at the correct angle. Plenty of factors to increase that number by a few more. The craft is very well stabilised so perhaps it would stay in or out of the right orientation for long periods.

 

[hutchphd]

Alternatively (?)

I do not think this is correct. The appropriate measure is the projected area of the mirror onto face of the sun. Because it is at about a half million miles distance this gives an additional factor of ~200 ² reproducing my (surprising) result
Another way to say this is how big would a shade have to be to completely eclipse the sun? About twice the radius of the moon at that distance. The hole should becompared to this area leading to the surprising magnitude 0 .
Am I screwing this up?

 

[sophiecentaur]

That looks reasonable. jWST is like a pretty big rock out there and we’d say it’s pretty close and a lot more reflective.

 

[TeethWhitener]

Am I screwing this up?

I’m wondering about this discrepancy too. I don’t see anything wrong with your calcs (I’m not an expert), but I don’t see anything wrong with the calcs in the link I posted either (different approach: take the max magnitude of the ISS and note that JWST is a factor of 4000 further away). It seems the reflected light from ISS is far more diffuse than I would have naively guessed.

I will go on record here and boldly predict that the magnitude of JWST will be $m=10\pm10$.

 

[hutchphd]

I will join that bold prediction. It seems to me also that "perfectly" flat for the mirror means angular surface undulations +/- (0.25º) about equal to half the angular size of the sun, assuming the pointing is on average correct to point the sun reflection at us. I don't know enough about how thay manipulate the shield to know whether there might be such a geometry. Keep looking up...near the full moon.

 

[collinsmark]

The real difficulty I'm having is trying to find ephemeris or ephemeris-like data for JWST, and how one would interpret it.

The problem is that most widely available programs (Stellarium, for example) that can keep track of the location of satellites use two-line element (TLE) data based off of Keplerian models, and assume the satellite is orbiting Earth (I've even written such a satellite tracking program myself!) But satellites orbiting L2? That's a curve-ball.

TLE data is meaningless for objects orbiting L2. Well, at least it's meaningless in TLEs' current format. I wonder if Stellarium will ever keep track of JWST, and if so, how they would go about doing it.

(At the time of this post, the Unistellar Optics website claims to give ephemeris results for JWST, but I fear it may be wrong. I suspect it's still using TLE data from back before JWST reached its L2 orbit. That's useless now. [Edit: Scratch that. I've personally verified that the Unistellar website calculator is a good resource and quite accurate.])

 

[collinsmark]

On second thought, perhaps the Unistellar Optics website is correct after all. At least it seems to agree with The Sky Live's JWST info calculator.

I suppose the next step is to check their results with my scope.

(I'm still really curious about their calculation algorithms though.)

 

[collinsmark]

I've resigned myself to give it a try tonight. Clear skies are forecast.

According to The Sky Live's and Unistellar's website calculators, JWST should be at
Right Ascension: 7h 20m 55s
Declination: 9^o 7' 12"
around the middle of the night (2022-Feb-05) from my location.
So I'll track those coordinates as soon they pass over my roof, and hope for the best.
According to my calculations, it should pass through a fairly significant portion of my sensor during the rest of the night when that patch of the sky is visible from my location.

I might have luck if JWST's magnitude is not much dimmer than 15 or so. Someone on stackexchange who's been tracking it estimates (based on their observations) it's been around magnitude 17 or 18 since reaching L2. That's not good news for me, but I don't believe everything I read on the Internet.

The challenge I face is taking longer exposures won't help much after a point; it will just make JWST trail longer, but not brighter. I'll try 300 sec (5 min) exposures. I doubt anything longer than that will help me.

Wish me luck.

 

[collinsmark]

Images are slowly coming in. Rather than flood this thread with new posts, I'll just update this post with any news. I'll make a new post with pics (maybe a video -- we'll see) once I've had a chance to process the data.

2022-02-06 05:00 UT:
I have good news and bad news to report.

• The good news is that The Sky Live's and Unistellar's website calculators are accurate. Surprisingly accurate (I'll update my previous posts to make that clear). And what's more, JWST is possible to image/track with an amateur telescope! Yay!
• The bad news is that it's just barely visible (with a cooled, long exposure camera). Again, I have a 10" SCT, and if I didn't know exactly where to look, I might have missed it. I haven't estimated its magnitude yet, but I'd guess that it's dimmer than +15. And +17 or +18 don't sound unreasonable.

Dark skies should go a long way when tracking JWST. Unfortunately for me, I'm imaging in Bortle 7 or 8 skies (that means I have a lot of light pollution). I'll continue updates as the night continues, because I might have better luck as the pertinent patch of sky moves away from some of worst causes of glare and skyglow. JWST crosses the meridian in less than one hour. I have slightly darker skies on the other side.

2022-02-06 06:04 UT:
JWST just crossed the meridian. 'Looks like a tiny, blurry line, at roughly the same brightness as the dimmest of stars my gear is capable of discerning at 300 sec (5 min) exposures. I'd guess it's slightly easier to pick out than before, but only slightly.

2022-02-06 06:22 UT:
Moon just set. That might help a little I hope.
I've also noticed multiple geosynchronous satellites in the data. They produce significantly longer and brighter trails than JWST. That should tell you how dim JWST is: way dimmer than a geosynchronous satellite.

2022-02-06 07:05 UT:
Omg, omg, omg. It just passed near a star and brightened up significantly for a couple of frames. It seems that some part of JWST is either reflecting, or perhaps diffracting (maybe edge diffraction) starlight! I never even considered that!

2022-02-06 08:08 UT:
Well, it's a couple of hours past the meridian. That usually means it's all downhill from here. I also just noticed that one of the nearby neighborhood lights that had thankfully burned out, was recently reinstalled. Darn it. JWST didn't get much clearer. It is still visible in the images, but at the bare minimum of the term.

2022-02-06 10:30 UT:
Aaand it's set behind a building/structure. Welp, that's it for tonight. We'll see if I can pull anything interesting out of it after flat/dark calibration and processing. Don't hold you breath for anything fantastic. 'Like I mentioned, the JWST was just barely visible in the images. But I should have something within a couple of days.

 

[sophiecentaur]

Moon setting will mean JWST could have already set, depending on its ephemeris. Something people will have to plan for that in a different way from other obs.

 

[hutchphd]

How precisely does the Webb point its sunshield at the sun? If it is very precise then the good reflection events may be more likely when it is passing through the ecliptic (?) I assume that will occur roughly six months post launch (or post final insertion ?). Probably the thermal pointing requirements are not that tight.

 

[sophiecentaur]

How precisely does the Webb point its sunshield at the sun? If it is very precise then the good reflection events may be more likely when it is passing through the ecliptic (?) I assume that will occur roughly six months post launch (or post final insertion ?). Probably the thermal pointing requirements are not that tight.

I can't actually see a picture of the deployed shield but it's unlikely to be a plane reflector. If it were, then it would be like a stealth aircraft which has mostly plane surfaces which are unlikely to bounce radar signals at a useful angle, sending sharp reflections upwards of sharply downwards. The fabric is under light tension but I can't think of any reason that it would have to be optically flat. So it's probably somewhere between a diffuse reflector and a set of fairly plane reflectors.

I'm pleased that my Noddy calculation of probable magnitude is not too far of a lot of other estimates on this thread. It can be soooo embarrassing to be orders of magnitude out. (The other sort of magnitude , I mean - or do I?)

 

[Motore]

I'm pleased that my Noddy calculation of probable magnitude is not too far of a lot of other estimates on this thread. It can be soooo embarrassing to be orders of magnitude out. (The other sort of magnitude , I mean - or do I?)

If your estimate was +9 (post #9) than per @collinsmark estimate of +16 it means that JWST is approx at least 500 to 1000 times dimmer than your estimate, so an order of maginute 2 to 3 out (the other sort of magnitude). ;)

 

[hutchphd]

If it were, then it would be like a stealth aircraft which has mostly plane surfaces which are unlikely to bounce radar signals at a useful angle

Because the sun subtends half a degree the flatness would need to be in that range. I was thinking more along the lines of an emergency signal mirror in the desert where we might see an occasional very bright glint as the mirror slowly swung through the magic alignment. Clearly that would be an absolute maximum possible signal. With the mirror not pointing at the magic angle you would get nothing.
If the mirror is instead a diffuse reflector then it is approximately a point source into the half space and one picks up a factor of $$ \frac {Area_{Webb}}{2\pi d_{Webb}^2} \approx 10^{-10} $$ which will reduce the magnitude by 25. So in fact I have cleverly bracketed the magnitude to $$m=13 \pm 13$$ Well done!

 

[sophiecentaur]

If your estimate was +9 (post #9) than per @collinsmark estimate of +16 it means that JWST is approx at least 500 to 1000 times dimmer than your estimate, so an order of maginute 2 to 3 out (the other sort of magnitude). ;)

And you’re saying that’s not near enough for jazz? You drive a hard bargain, young man.

And I’d love a link with an image of that sunscreen. Poor thing seems to get no recognition yet it’s doing a great job and the deployment was very impressive.

 

[collinsmark]

Here's a YouTube version of the data. It suffers from compression artifacts, but, well, it seems it can't be helped.

Notice the reflections when JWST passes slightly North of a couple of stars. It may be best viewed fullscreen.



Now I need to get some sleep.

 

[TeethWhitener]

Outstanding work @collinsmark ! Is the brightening an artifact of some kind? I don’t know anything about astrophotography.

 

[collinsmark]

Outstanding work @collinsmark ! Is the brightening an artifact of some kind? I don’t know anything about astrophotography.

I speculate that those brief intervals of brightening are some sort of reflection of starlight from behind JWST. It seemed correlated with passing just a bit north of stars, by just the right amount. That's just my speculation though. I don't know for certain.

 

[hutchphd]

Ever see an emergency signal mirror flash in daylight ? I think the heat shield is largely specular reflecting and occasionally points the sun back at us. See several previous entries.
Nice stuff.

 

[sophiecentaur]

Here's a YouTube version of the data. It suffers from compression artifacts, but, well, it seems it can't be helped.

Notice the reflections when JWST passes slightly North of a couple of stars. It may be best viewed fullscreen.



Now I need to get some sleep.

Great movie (and you needed confidence to see it through, too. You'll be confident that the next one will / should give results.
What length of time does the movie cover? I'm wondering how much the reflection angles could be changing, to account for the varying brightness. A good image of the sunshield would help us appreciate what could be going on.

 

[collinsmark]

Great movie (and you needed confidence to see it through, too. You'll be confident that the next one will / should give results.
What length of time does the movie cover? I'm wondering how much the reflection angles could be changing, to account for the varying brightness. A good image of the sunshield would help us appreciate what could be going on.

It covers about 5 hours. There's a timestamp at the upper left of the video, so you can see the exact time of the imaging.

The neat thing about JWST's L2 orbit is that JWST is visible to everyone* every night, clouds allowing. It will always be within around 26 degrees or less of the intersection of the ecliptic and meridian at your local midnight. This is true regardless of season or moon phase. It's up every night for everybody*.

*(People in higher latitudes [near arctic and antarctic] might have issue with this. So, yes, there can be exceptions from time to time.)

I've put a animated GIF on the Internet that doesn't have as many compression artifacts. It's too big to embed here though (37 MB). Here's a link to it if anyone's interested:
http://www.shadycrypt.com/PF/JWST_Feb2022_2.gif

 

[collinsmark]

I'm wondering how much the reflection angles could be changing, to account for the varying brightness. A good image of the sunshield would help us appreciate what could be going on.

According to my eyballing together with Stellarium as a reference, it seems to travel a little over 9 arcminutes in that 5 hour interval. So that corresponds to just over 1.8 arcseconds per minute.

The flares last just a little over 15 minutes or so, roughly. So that's an angular change (angular change of JWST as seen from my telescope's location on Earth, with respect to the background stars) of about 27 arcseconds per flare. (0.0075^o per flare.)

 

[hutchphd]

According to my eyballing together with Stellarium as a reference, it seems to travel a little over 9 arcminutes in that 5 hour interval. So that corresponds to just over 1.8 arcseconds per minute.

Sanity check:
This just corresponds to roughly a degree per day which is the sweep of the Sun- Earth- L2 line right?
It is motion of JWST relative to that line that would cause the flareups if they are what I suspect. Are we on the same page?

 

[collinsmark]

Sanity check:
This just corresponds to roughly a degree per day which is the sweep of the Sun- Earth- L2 line right?
It is motion of JWST relative to that line that would cause the flareups if they are what I suspect. Are we on the same page?

Right. That calculation is in respect to the background stars. But as you point out, L2 is moving with respect to the background stars too.

So if we want to subtract out the L2 motion, we have some pretty complicated geometry to do.

I haven't done that geometry. (At least not yet.) To start, the image is non-inverted (it's not a mirror image), and its rotational orientation is less than +/- 0.5 deg. So let's just go with 0 deg rotation. That means North is up, South is down, East is to the Right, and South is to the Left. That's all relative to Earth's celestial pole (not relative to the ecliptic pole -- that's one of the coordinate transformations that would have to be done).

I just noticed that Stellarium has the ability to overlay ecliptic coordinates over its view. Let me try to do some more eyeballing with that.

 

[hutchphd]

So if we want to subtract out the L2 motion,

Motion relative to what? I am still not following what you are trying to do I guess.

 

[collinsmark]

Motion relative to what? I am still not following what you are trying to do I guess.

All the eyballing in my previous posts was done relative to the background stars from the point of view of my telescope.

But L2 is moving with respect to the background stars, from the point of view of my telescope. That's okay though, because JWST is not rotating relative to the background stars. (I assume it's calibrating its instrumentation at this time, and pointing at the same star.) It is however, rotating with respect to the Sun.

So in reference to my telescope (pointing at a constant direction relative the background stars), JWST's apparent illumination by the sun (as seen from my telescope) is changing for several reasons:

• JWST is rotating relative to the sun, to keep up with the revolving L2 position. (Earth is revolving at the same rate for this one. But JWST is rotating to compensate for this [this assumes it's pointing at a star])
• JWST is orbiting its L2 point, changing it's position relative to the Sun-Earth-L2 line.
• The surface of the Earth is moving relative to the line of Sun-Earth-L2, due to the Earth's rotation

If we were to analyze this further, to determine how much corresponds to each, we would need to break it down a bit more.

 

[hutchphd]

• JWST is rotating relative to the sun, to keep up with the revolving L2 position. (Earth is revolving at the same rate for this one. But JWST is rotating to compensate for this [this assumes it's pointing at a star])
• JWST is orbiting its L2 point, changing it's position relative to the Sun-Earth-L2 line.
• The surface of the Earth is moving relative to the line of Sun-Earth-L2, due to the Earth's rotation

I understand 2 and 3 and agree. But for 1 you are saying the sun-earth-L2 line is rotating nce a year but the Webb primary mirror axis is fixed on a star. Is the heat mirror axis rigidly fixed wrt the primary axis? I guess it must be?