<p>We can use the same expression that is commonly used to estimate the apparent magnitude of a planet or asteroid in the Solar System*:</p>
<p><span class="math-container">$$\boxed{m=5 \log \frac{1329}{d \cdot \sqrt p}+5 \log (D_s \cdot D_e)-2.5\log f(F)}$$</span></p>
<p>Where:</p>
<p><strong>m</strong> is the apparent magnitude</p>
<p><strong>log</strong> is the decimal logarithm</p>
<p><strong>d</strong> is the diameter in km</p>
<p><strong>p</strong> is the albedo</p>
<p><strong>Ds</strong> is the distance to the Sun in Astronomical Units (AU)</p>
<p><strong>De</strong> is the distance to Earth in Astronomical Units (AU)</p>
<p><strong>f(F)</strong> is the phase function</p>
<p>If we want to apply this expression to the James Webb Space Telescope, the values to use are as follows.</p>
<p>As the surface area of the JWST solar shield is <span class="math-container">$S=21\cdot 14=294$</span> square meters:</p>
<p><span class="math-container">$$d=\sqrt{\frac{4\cdot S}{\pi}}$$</span></p>
<p>Equivalent diameter &quot;d&quot;</p>
<p><strong>d = 0.01935 km</strong></p>
<p>The satellite hosting the Webb Telescope will be placed in a halo orbit around Lagrange L2 Sun-Earth, a point located 1.5 million kilometers from the Earth (see drawing). The radius of the halo orbit is 0.8 million km.</p>
<p><span class="math-container">$$D_e=\sqrt{1.5^2+0.8^2}=1.7$$</span></p>
<p><strong>De = 0.01136 AU</strong></p>
<p><strong>Ds = 1.01004 AU</strong></p>
<p>As a phase function we will use the usual one:</p>
<p><span class="math-container">$$f(F)=\dfrac{1+\cos F}2$$</span></p>
<p>The phase angle &quot;F&quot; is calculated using basic trigonometry from the drawing</p>
<p><a href="https://i.sstatic.net/1Nj2f.png" rel="noreferrer"><img src="https://i.sstatic.net/1Nj2f.png" alt="Webb position" /></a></p>
<p>It is obtained:</p>
<p><strong>F = 27.8º</strong></p>
<p>And we see that the contribution of the corresponding summand is almost negligible:</p>
<p><span class="math-container">$$-2.5 \log f(F)=+0.06$$</span></p>
<p>The albedo &quot;p&quot; of the heat shield will be high, to reflect the maximum amount of heat possible. But since the albedo of the solar shield is unknown to me, I add the table below showing the estimated apparent magnitude value, for different albedo values.</p>
<p><a href="https://i.sstatic.net/e5rsJ.png" rel="noreferrer"><img src="https://i.sstatic.net/e5rsJ.png" alt="magnitude vs albedo table" /></a></p>
<p>The table tells us that <strong>the apparent magnitude of the JWST</strong> when it reaches its halo orbit around L2 <strong>will be of the order of +15</strong> and therefore this should be visible with some powerful telescopes of amateur astronomers.</p>
<p>*Reference: <a href="https://www.asu.cas.cz/%7Eppravec/pravecharris07.pdf" rel="noreferrer"><strong>Binary asteroid population. 1. Angular momentum content</strong>, by P. Pravec and A.W. Harris</a></p>
<p>Best regards.</p>

CC BY-SA 4.0
2022-01-18T19:19:27.183Z
`+1` and you may be interesting in adding an answer to [Good source for the relationship between absolute magnitude, diameter, and albedo?](https://astronomy.stackexchange.com/q/26017/7982) I'm still trying to find a citable, authoritative source (or derive) the term $$\log_{10}(1329)$$ Different but related questions: [When would we detect a tiny meter size natural satellite in a geostationary orbits?](https://astronomy.stackexchange.com/q/29957/7982) and [Calculating the apparent magnitude of a satellite](https://astronomy.stackexchange.com/q/28744/7982)
uhoh
CC BY-SA 4.0
2022-01-18T11:43:14.147Z
2022-01-19T08:12:53.437Z
2022-01-19T08:12:53.437Z
Albert
<p>I have been imaging the JWST with a Celestron C11 almost every clear night since January 4th. After it arrived at L2 I estimate the magnitude around 17 or 18 based on asteroids about that magnitude that I have imaged.  I caught a significant brief brightening that can be seen in this set of images <a href="https://www.flickr.com/photos/mjzuraw/51845428333/in/photostream/" rel="noreferrer">https://www.flickr.com/photos/mjzuraw/51845428333/in/photostream/</a> It should be possible to predict these brighting or flaring events much like they do for iridium satellites.</p>

CC BY-SA 4.0
2022-02-13T17:17:32.283Z
I photographed the JWST and two asteroids in the same image on 2/10/22.  https://www.flickr.com/photos/mjzuraw/51876261098/in/dateposted/  Based on the published predicted brightness of the two asteroids, the JWST was dimmer than magnitude 17.6.
Michael Zuraw
CC BY-SA 4.0
2022-01-29T04:21:36.033Z
2022-01-29T04:21:36.033Z
Michael Zuraw
<p>One of the problems with imaging GAIA is that the satellite is moving fairly rapidly with respect to the stars so increase the exposure time does not make the image any brighter. Since JWST is in a larger halo orbit it may have a higher apparent motion so is more difficult to image. If you can track JWST it may be easier to image but of course the stars will trail.</p>

CC BY-SA 4.0
2022-01-07T22:14:54.013Z
Since GAIA's trajectory and therefore its own proper motion is known, you could certainly track it instead of the stars during a long exposure, and then its image would definitely get brighter when increasing exposure time.  For example [Help me understand these tweeted images of JWST moving through Orion!](https://space.stackexchange.com/q/57454/12102) links to [this](https://twitter.com/Skysurfer77x/status/1475805919430815753). This kind of object tracking is pretty standard and used on comets and asteroids as well.
uhoh
CC BY-SA 4.0
2022-01-07T22:35:55.547Z
The GIF in [this answer](https://astronomy.stackexchange.com/a/33695/7982) is a really dramatic example of this kind of tracking, you can see stars "shoot past" it. See also [Fastest recorded apparent motion of a comet or asteroid seen from Earth (degrees/day)?](https://astronomy.stackexchange.com/q/33697/7982) and [Which are stars and which are noise in this comet photo?](https://astronomy.stackexchange.com/q/33681/7982)
uhoh
CC BY-SA 4.0
2022-01-07T21:02:54.593Z
2022-01-07T21:02:54.593Z
JohnM
<p>At 1.5 million km JWST will be roughly 4,000 times farther than the ISS when it's overhead, and very roughly a tenth of the cross-section.</p>
<p>So if the ISS can be as bright as -4 magnitude, then JWST will be very roughly +16. That's well within the range of small observatories and large amateur telescopes.</p>
<p>But there is going to be quite a lot of variability in this!</p>
<p>Since we're in the same direction as the Sun, JWST's 20 x 15 meter sunshield is going to act like a diffuse mirror.</p>
<p>A good quality mirror in the sun still looks almost black if it's clean and reflecting a dark area of the sky, and super-bright if reflecting the Sun. But the heat-shield while reflective will have some amount of diffuseness.</p>
<p>And as the telescope points in different direction, the normal to the heatshield's surface can point almost directly towards us or actually  tens of degrees away.</p>
<p>So I expect that once in orbit and under operation, JWST's brightness will vary a lot depending on where it's looking.</p>
<hr />
<p>All the answers are helpful but <a href="https://space.stackexchange.com/a/31693/12102">@astrosnapper's answer</a> provides links to the data showing that a 1 meter telescope tracked SpaceX Starman/Roadster from magnitude +16 all the way down past +21.</p>
<p>So amateurs with good telescope should be able to track it in deep space on its several-month trip out to its Sun-Earth L2 halo orbit and follow it there.</p>
<p>An object associated with the Sun-Earth Lagrange points is really in orbit around the Sun, but because of Earth's nudging gravity has become in a resonant orbit with Earth as well.</p>
<p>As seen from Earth, the Sun-Earth L2 point itself travels the ecliptic at a point exactly opposite the Sun. But JWST's big halo orbit will cause it to appear to wiggle up and down by about 10 or 15 degrees from the ecliptic roughly twice a year.</p>
<p><strong>Lower your volume</strong> before watching the video:</p>
<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/v6ihVeEoUdo?start=571"></iframe>
            </div></div></p>

CC BY-SA 4.0
2021-09-16T15:49:01.220Z
The Ground-based Optical Tracking of Gaia (GBOT) project ([GBOT site](https://gbot.obspm.fr)) regularly tracks the Gaia satellite out at L2 using ~2m telescopes. Its brightness is somewhat wavelength dependent but around 20. This was fainter than expected based on tests done with WMAP and Planck which were also out at L2, despite the similar spacecraft sizes and shapes. I don't know of any pre-launch modelling of the JWST brightness so we'll have to see once it gets to orbit and into the operational configuration.
astrosnapper
CC BY-SA 4.0
2021-09-16T16:42:34.270Z
@astrosnapper thanks for the update!
uhoh
CC BY-SA 4.0
2021-12-30T02:10:37.737Z
The exact magnitude of JWST is hard to calculate, because while the sun shield will reflect almost specualarly, its shape is not flat but somewhat saddle shaped. From discussions in the astronomer FB group, it seems mag 17-18 is the best we can hope for. Still visible in a relatively cheap telescope though.
pela
CC BY-SA 4.0
2021-12-30T03:22:45.867Z
@pela interesting! To an astronomer "visible in a relatively cheap telescope" might mean something different than to the lay public. If I go and buy a \$50 telescope and look through it expecting to see +17 magnitude I might be disappointed, but if an astrophotographer gets a used 30 cm for \$500 and has a programmable DLSR already laying around they might do quite nicely.
uhoh
CC BY-SA 4.0
2021-12-30T19:33:08.983Z
No I think we probably agree on what is cheap, but I hadn't thought it through — to see a 17th magnitude object, you would need a 1-m class telescope, which is definitely not cheap. But with a cheap telescope and a _camera_, it shouldn't be too difficult (although you might have to do some sky background subtraction).
pela
CC BY-SA 4.0
2022-01-06T16:05:08.097Z
Current status on the visibility of JWST: My colleague took [this picture](https://www.facebook.com/cosmicdawncenter/photos/a.132455965097243/436754671334036) through his 11.5 cm telescope with 2 min's exposure. A rough estimate based on the surrounding stars is that JWST is currently V ~ 16, although it fluctuates somewhat. Since it's currently 1e6 km away, in L2 it will be 1.5 more distant, so 1.5² times fainter, or roughly one mag.
pela
CC BY-SA 4.0
2022-01-06T21:56:12.793Z
@pela Oh that is so cool! Was it easily found using the trajectory in JPL's horizons (or similar) or did they have to hunt for it?
uhoh
CC BY-SA 4.0
2022-01-10T14:15:56.350Z
The ephemeris can be found here: [unistellaroptics.com/observe-jwst](https://unistellaroptics.com/observe-jwst). I don't know how easy it was, though.
pela
CC BY-SA 4.0
2022-01-10T20:37:31.607Z
@pela Interesting! The example gives an exposure time of 4 seconds at a gain of 25 dB, I'm guessing that's ADC gain for a specific camera/telescope combination? I think the ephemeris function might just be a front-end for JPL Horizons or a local SPICE implementation using JPL's SPKs, as it says "Source: JPL ephemeris" at the bottom of the ephemeris page. https://i.sstatic.net/Gk0eY.png So I wondered if it also uses the predicted apparent magnitude from there, but it seems at least Horizons doesn't generate one https://i.sstatic.net/cUHxT.png so they may be doing it themselves.
uhoh
CC BY-SA 4.0
2022-01-10T20:41:55.790Z
@pela I couldn't get it to display an ephemeris on my computer, it seems geared for cellphone use, perhaps with a telescope app already running. I can generate some [ephemerides](https://english.stackexchange.com/q/370655/217285) but the links https://i.sstatic.net/jvyLB.png look non-url like this: `unistellar://science/defense?ra=102.68261&dec=4.27572&et=3971&g=25&d=2400&t=1642744800` (midnight in [Paris, Texas](https://en.wikipedia.org/wiki/Paris,_Texas_(film))). Have you been able to see magnitude predictions from it on a computer without a special app?
uhoh
CC BY-SA 4.0
2022-01-11T12:51:33.443Z
I haven't been using this myself, but I think you're right that it's just a frontend for JPL. And yes, it's purpose seems to be particularly for the Unistellar App, although you can also just click the ⌄ icon to expand and see the coordinates. I get a similar URL to you, but don't really understand; it gives the same gain (g) and exposure time (et) for all times and locations, it seems.
pela
CC BY-SA 4.0
2021-09-16T14:49:52.180Z
2021-12-30T00:52:24.763Z
2021-12-30T00:52:24.763Z
uhoh
<p>Once the JWST is in orbit around L2, would it be possible to view it using any ground based telescopes? I’m mostly thinking of equipment available to amateurs, since I don’t have a 10m reflector. But would this be feasible for anything we have built or could build on the ground?</p>

CC BY-SA 4.0
2022-01-06T20:28:21.360Z
I imaged it with a 14 inch SCT and a CMOS video camera. No problem.
Clif Ashcraft
CC BY-SA 4.0
2022-01-06T22:21:30.420Z
Any chance you would want to share it?
user287095
CC BY-SA 4.0
2022-07-06T20:22:16.257Z
Related: Gaia space telescope images Webb 1 million km away via sky mapper instrument: [Gaia snaps photo of Webb at L2](https://phys.org/news/2022-03-gaia-snaps-photo-webb-l2.html)
nealmcb
<james-webb-space-telescope>
Will the James Webb Space Telescope be visible from earth?
user287095
# Will the James Webb Space Telescope be visible from earth?

(Asked by: username_0 on 2021-09-16)

Once the JWST is in orbit around L2, would it be possible to view it using any ground based telescopes? I’m mostly thinking of equipment available to amateurs, since I don’t have a 10m reflector. But would this be feasible for anything we have built or could build on the ground?

**Tags:** james-webb-space-telescope
> **Comments:**
> **username_1**: I imaged it with a 14 inch SCT and a CMOS video camera. No problem.  
> **username_0**: Any chance you would want to share it?  
> **username_2**: Related: Gaia space telescope images Webb 1 million km away via sky mapper instrument: [Gaia snaps photo of Webb at L2](https://phys.org/news/2022-03-gaia-snaps-photo-webb-l2.html)  

---

## 4 answers

### Answer by username_4 on 2021-09-16. Score: 13 | Accepted answer

At 1.5 million km JWST will be roughly 4,000 times farther than the ISS when it's overhead, and very roughly a tenth of the cross-section.

So if the ISS can be as bright as -4 magnitude, then JWST will be very roughly +16. That's well within the range of small observatories and large amateur telescopes.

But there is going to be quite a lot of variability in this!

Since we're in the same direction as the Sun, JWST's 20 x 15 meter sunshield is going to act like a diffuse mirror.

A good quality mirror in the sun still looks almost black if it's clean and reflecting a dark area of the sky, and super-bright if reflecting the Sun. But the heat-shield while reflective will have some amount of diffuseness.

And as the telescope points in different direction, the normal to the heatshield's surface can point almost directly towards us or actually tens of degrees away.

So I expect that once in orbit and under operation, JWST's brightness will vary a lot depending on where it's looking.

---

All the answers are helpful but [@astrosnapper's answer](https://space.stackexchange.com/a/31693/12102) provides links to the data showing that a 1 meter telescope tracked SpaceX Starman/Roadster from magnitude +16 all the way down past +21.

So amateurs with good telescope should be able to track it in deep space on its several-month trip out to its Sun-Earth L2 halo orbit and follow it there.

An object associated with the Sun-Earth Lagrange points is really in orbit around the Sun, but because of Earth's nudging gravity has become in a resonant orbit with Earth as well.

As seen from Earth, the Sun-Earth L2 point itself travels the ecliptic at a point exactly opposite the Sun. But JWST's big halo orbit will cause it to appear to wiggle up and down by about 10 or 15 degrees from the ecliptic roughly twice a year.

**Lower your volume** before watching the video:

> **Comments:**
> **username_7**: The Ground-based Optical Tracking of Gaia (GBOT) project ([GBOT site](https://gbot.obspm.fr)) regularly tracks the Gaia satellite out at L2 using ~2m telescopes. Its brightness is somewhat wavelength dependent but around 20. This was fainter than expected based on tests done with WMAP and Planck which were also out at L2, despite the similar spacecraft sizes and shapes. I don't know of any pre-launch modelling of the JWST brightness so we'll have to see once it gets to orbit and into the operational configuration.  
> **username_4**: @astrosnapper thanks for the update!  
> **username_8**: The exact magnitude of JWST is hard to calculate, because while the sun shield will reflect almost specualarly, its shape is not flat but somewhat saddle shaped. From discussions in the astronomer FB group, it seems mag 17-18 is the best we can hope for. Still visible in a relatively cheap telescope though.  
> **username_4**: @pela interesting! To an astronomer "visible in a relatively cheap telescope" might mean something different than to the lay public. If I go and buy a \$50 telescope and look through it expecting to see +17 magnitude I might be disappointed, but if an astrophotographer gets a used 30 cm for \$500 and has a programmable DLSR already laying around they might do quite nicely.  
> **username_8**: No I think we probably agree on what is cheap, but I hadn't thought it through — to see a 17th magnitude object, you would need a 1-m class telescope, which is definitely not cheap. But with a cheap telescope and a _camera_, it shouldn't be too difficult (although you might have to do some sky background subtraction).  
> **username_8**: Current status on the visibility of JWST: My colleague took [this picture](https://www.facebook.com/cosmicdawncenter/photos/a.132455965097243/436754671334036) through his 11.5 cm telescope with 2 min's exposure. A rough estimate based on the surrounding stars is that JWST is currently V ~ 16, although it fluctuates somewhat. Since it's currently 1e6 km away, in L2 it will be 1.5 more distant, so 1.5² times fainter, or roughly one mag.  
> **username_4**: @pela Oh that is so cool! Was it easily found using the trajectory in JPL's horizons (or similar) or did they have to hunt for it?  
> **username_8**: The ephemeris can be found here: [unistellaroptics.com/observe-jwst](https://unistellaroptics.com/observe-jwst). I don't know how easy it was, though.  
> **username_4**: @pela Interesting! The example gives an exposure time of 4 seconds at a gain of 25 dB, I'm guessing that's ADC gain for a specific camera/telescope combination? I think the ephemeris function might just be a front-end for JPL Horizons or a local SPICE implementation using JPL's SPKs, as it says "Source: JPL ephemeris" at the bottom of the ephemeris page. https://i.sstatic.net/Gk0eY.png So I wondered if it also uses the predicted apparent magnitude from there, but it seems at least Horizons doesn't generate one https://i.sstatic.net/cUHxT.png so they may be doing it themselves.  
> **username_4**: @pela I couldn't get it to display an ephemeris on my computer, it seems geared for cellphone use, perhaps with a telescope app already running. I can generate some [ephemerides](https://english.stackexchange.com/q/370655/217285) but the links https://i.sstatic.net/jvyLB.png look non-url like this: `unistellar://science/defense?ra=102.68261&dec=4.27572&et=3971&g=25&d=2400&t=1642744800` (midnight in [Paris, Texas](https://en.wikipedia.org/wiki/Paris,_Texas_(film))). Have you been able to see magnitude predictions from it on a computer without a special app?  
> **username_8**: I haven't been using this myself, but I think you're right that it's just a frontend for JPL. And yes, it's purpose seems to be particularly for the Unistellar App, although you can also just click the ⌄ icon to expand and see the coordinates. I get a similar URL to you, but don't really understand; it gives the same gain (g) and exposure time (et) for all times and locations, it seems.  

---

### Answer by username_3 on 2022-01-18. Score: 9

We can use the same expression that is commonly used to estimate the apparent magnitude of a planet or asteroid in the Solar System\*:

$$\boxed{m=5 \log \frac{1329}{d \cdot \sqrt p}+5 \log (D\_s \cdot D\_e)-2.5\log f(F)}$$

Where:

**m** is the apparent magnitude

**log** is the decimal logarithm

**d** is the diameter in km

**p** is the albedo

**Ds** is the distance to the Sun in Astronomical Units (AU)

**De** is the distance to Earth in Astronomical Units (AU)

**f(F)** is the phase function

If we want to apply this expression to the James Webb Space Telescope, the values to use are as follows.

As the surface area of the JWST solar shield is $S=21\cdot 14=294$ square meters:

$$d=\sqrt{\frac{4\cdot S}{\pi}}$$

Equivalent diameter "d"

**d = 0.01935 km**

The satellite hosting the Webb Telescope will be placed in a halo orbit around Lagrange L2 Sun-Earth, a point located 1.5 million kilometers from the Earth (see drawing). The radius of the halo orbit is 0.8 million km.

$$D\_e=\sqrt{1.5^2+0.8^2}=1.7$$

**De = 0.01136 AU**

**Ds = 1.01004 AU**

As a phase function we will use the usual one:

$$f(F)=\dfrac{1+\cos F}2$$

The phase angle "F" is calculated using basic trigonometry from the drawing

[![Webb position](https://i.sstatic.net/1Nj2f.png)](https://i.sstatic.net/1Nj2f.png)

It is obtained:

**F = 27.8º**

And we see that the contribution of the corresponding summand is almost negligible:

$$-2.5 \log f(F)=+0.06$$

The albedo "p" of the heat shield will be high, to reflect the maximum amount of heat possible. But since the albedo of the solar shield is unknown to me, I add the table below showing the estimated apparent magnitude value, for different albedo values.

[![magnitude vs albedo table](https://i.sstatic.net/e5rsJ.png)](https://i.sstatic.net/e5rsJ.png)

The table tells us that **the apparent magnitude of the JWST** when it reaches its halo orbit around L2 **will be of the order of +15** and therefore this should be visible with some powerful telescopes of amateur astronomers.

\*Reference: [**Binary asteroid population. 1. Angular momentum content**, by P. Pravec and A.W. Harris](https://www.asu.cas.cz/%7Eppravec/pravecharris07.pdf)

Best regards.

> **Comments:**
> **username_4**: `+1` and you may be interesting in adding an answer to [Good source for the relationship between absolute magnitude, diameter, and albedo?](https://astronomy.stackexchange.com/q/26017/7982) I'm still trying to find a citable, authoritative source (or derive) the term $$\log_{10}(1329)$$ Different but related questions: [When would we detect a tiny meter size natural satellite in a geostationary orbits?](https://astronomy.stackexchange.com/q/29957/7982) and [Calculating the apparent magnitude of a satellite](https://astronomy.stackexchange.com/q/28744/7982)  

---

### Answer by username_5 on 2022-01-29. Score: 6

I have been imaging the JWST with a Celestron C11 almost every clear night since January 4th. After it arrived at L2 I estimate the magnitude around 17 or 18 based on asteroids about that magnitude that I have imaged. I caught a significant brief brightening that can be seen in this set of images <https://www.flickr.com/photos/mjzuraw/51845428333/in/photostream/> It should be possible to predict these brighting or flaring events much like they do for iridium satellites.

> **Comments:**
> **username_5**: I photographed the JWST and two asteroids in the same image on 2/10/22.  https://www.flickr.com/photos/mjzuraw/51876261098/in/dateposted/  Based on the published predicted brightness of the two asteroids, the JWST was dimmer than magnitude 17.6.  

---

### Answer by username_6 on 2022-01-07. Score: 2

One of the problems with imaging GAIA is that the satellite is moving fairly rapidly with respect to the stars so increase the exposure time does not make the image any brighter. Since JWST is in a larger halo orbit it may have a higher apparent motion so is more difficult to image. If you can track JWST it may be easier to image but of course the stars will trail.

> **Comments:**
> **username_4**: Since GAIA's trajectory and therefore its own proper motion is known, you could certainly track it instead of the stars during a long exposure, and then its image would definitely get brighter when increasing exposure time.  For example [Help me understand these tweeted images of JWST moving through Orion!](https://space.stackexchange.com/q/57454/12102) links to [this](https://twitter.com/Skysurfer77x/status/1475805919430815753). This kind of object tracking is pretty standard and used on comets and asteroids as well.  
> **username_4**: The GIF in [this answer](https://astronomy.stackexchange.com/a/33695/7982) is a really dramatic example of this kind of tracking, you can see stars "shoot past" it. See also [Fastest recorded apparent motion of a comet or asteroid seen from Earth (degrees/day)?](https://astronomy.stackexchange.com/q/33697/7982) and [Which are stars and which are noise in this comet photo?](https://astronomy.stackexchange.com/q/33681/7982)  

---

