<p>A blurred fogscape. Even if JW could ever point at such low elongations, motion at (nominally) L2 exceeds the observatory panning specification, and you’d get an image of whatever the relative motion vector was.</p>

CC BY-SA 4.0
2022-08-04T02:20:56.717Z
Fascinating. Can you expand on the angular motion of Earth vs the Webb orbit, and compare it to the panning spec? With a reference?
nealmcb
CC BY-SA 4.0
2022-11-06T22:01:37.510Z
So, "speed blur"
Criggie
CC BY-SA 4.0
2022-08-01T22:22:08.393Z
2022-08-01T22:22:08.393Z
caInstrument
<p>The best angular resolution of JWST is about 0.07 arcseconds and the telescope is 1.5 million km from Earth.</p>
<p>Ignoring any blurring due to the Earth's atmosphere, this translates to about 500 m on the Earth's surface.</p>
<p>The field of view (of the NIRCAM instrument) would cover about 1000 km on the Earth.</p>
<p>Whether you would actually see any details is moot, since the Earth would be in the same direction as, but closer, than the Sun. I guess you would see features in the infrared due to temperature differences.</p>

CC BY-SA 4.0
2022-07-17T15:37:08.287Z
so, the resolution is about the same as regular Earth viewing cameras - which are often 2000 times closer (750 km) and get about 1500 times better resolution (30 cm). Disappointing, in some sense.
asdfex
CC BY-SA 4.0
2022-07-18T04:26:46.687Z
hopefully some of the imaging arrays will still work after being warmed by the Earth's thermal radiation.
uhoh
CC BY-SA 4.0
2022-07-17T15:29:17.640Z
2022-07-17T15:39:06.577Z
2022-07-17T15:39:06.577Z
ProfRob
<p>I have seen comparisons of the picture quality between Hubble and Webb, and I have read that the size of the pictures Webb is taking is akin to holding a grain of sand at arms length against the sky.</p>
<p>Still, I'm not able to comprehend how far these objects are or have a grasp on how much light is coming through.</p>
<p>I thought then that, hypothetically, if Webb would be pointed at Earth, and would be able to capture at similar range (ignoring all the impossibilities of doing so), what would show up in the pictures? A house? A pixel in a monitor? Molecules?</p>

CC BY-SA 4.0
2022-07-17T14:52:04.527Z
Before you had the chance to see anything, you would be assaulted by all the physicists and engineers that worked for decades on how to keep it cool, e.g. by never pointing it toward Earth.
pela
CC BY-SA 4.0
2022-07-18T01:31:34.100Z
Pointing it to Earth would screw up not just the cooling, but the cameras themselves probably. But as you said, we are ignoring those impossibilities.
Victor Stafusa
<james-webb-space-telescope>
What would James Webb Space Telescope be able to see if pointed at Earth?
Victor Debone
# What would James Webb Space Telescope be able to see if pointed at Earth?

(Asked by: username_0 on 2022-07-17)

I have seen comparisons of the picture quality between Hubble and Webb, and I have read that the size of the pictures Webb is taking is akin to holding a grain of sand at arms length against the sky.

Still, I'm not able to comprehend how far these objects are or have a grasp on how much light is coming through.

I thought then that, hypothetically, if Webb would be pointed at Earth, and would be able to capture at similar range (ignoring all the impossibilities of doing so), what would show up in the pictures? A house? A pixel in a monitor? Molecules?

**Tags:** james-webb-space-telescope
> **Comments:**
> **username_1**: Before you had the chance to see anything, you would be assaulted by all the physicists and engineers that worked for decades on how to keep it cool, e.g. by never pointing it toward Earth.  
> **username_2**: Pointing it to Earth would screw up not just the cooling, but the cameras themselves probably. But as you said, we are ignoring those impossibilities.  

---

## 2 answers

### Answer by username_6 on 2022-07-17. Score: 5 | Accepted answer

The best angular resolution of JWST is about 0.07 arcseconds and the telescope is 1.5 million km from Earth.

Ignoring any blurring due to the Earth's atmosphere, this translates to about 500 m on the Earth's surface.

The field of view (of the NIRCAM instrument) would cover about 1000 km on the Earth.

Whether you would actually see any details is moot, since the Earth would be in the same direction as, but closer, than the Sun. I guess you would see features in the infrared due to temperature differences.

> **Comments:**
> **username_7**: so, the resolution is about the same as regular Earth viewing cameras - which are often 2000 times closer (750 km) and get about 1500 times better resolution (30 cm). Disappointing, in some sense.  
> **username_8**: hopefully some of the imaging arrays will still work after being warmed by the Earth's thermal radiation.  

---

### Answer by username_3 on 2022-08-01. Score: 3

A blurred fogscape. Even if JW could ever point at such low elongations, motion at (nominally) L2 exceeds the observatory panning specification, and you’d get an image of whatever the relative motion vector was.

> **Comments:**
> **username_4**: Fascinating. Can you expand on the angular motion of Earth vs the Webb orbit, and compare it to the panning spec? With a reference?  
> **username_5**: So, "speed blur"  

---

