<p>There is a physical limit to the angular resolution of any imaging system. For a circular aperture it is often quoted that the angular resolution corresponds to around <span class="math-container">$\theta_{\rm min} = 1.22 \lambda/D$</span> (in radians), where <span class="math-container">$\lambda$</span> is the wavelength of observation and <span class="math-container">$D$</span> is the diameter of the telescope.</p>

<p>A similar limit applies in interferometry but now <span class="math-container">$D$</span> might represent the separation between your telescopes.</p>

<p>To translate an angular resolution to an actual physical resolution of size you would have to multiply by the distance to the source.</p>

<p>So the ways in which you can improve matters are:</p>

<ol>
<li>Use a bigger telescope or use an interferometer with a longer baseline.</li>
<li>Work at shorter wavelengths.</li>
<li>Get closer to the source.</li>
</ol>

<p>There are of course technical challenges with each of these. In particular you might have thought just increasing the baseline would be easy enough - but you need to know the separation of your telescope to a fraction of the wavelength you are using and that turns out to be tough for larger separations. Shorter wavelengths are problematic for optics - normal lenses and mirrors don't work at X-ray wavelengths for example. Getting closer to the source requires interstellar travel...</p>

<p>The OP wants to argue with me about whether the atmosphere is a significant factor. Of course the atmosphere degrades stellar images (it's not diffraction, but refraction). Going into space overcomes this and <strong>in the past</strong> this <strong>would</strong> have been the limiting issue. However, now it is commonplace for ground-based telescopes to achieve close to their diffraction-limited performance using adaptive optics techniques or "<a href="https://en.m.wikipedia.org/wiki/Lucky_imaging" rel="nofollow noreferrer">Lucky Imaging</a>", both of which can and have got better images than the Hubble Space Telescope (examples below).</p>

<p>Example 1: <em>The middle picture is from HST, the right hand image is Lucky Imaging from the ground based Palomar 5m telescope. The larger aperture of the Palomar produces better resolution despite looking through the atmosphere.</em> See <a href="https://www.ast.cam.ac.uk/research/lucky" rel="nofollow noreferrer">https://www.ast.cam.ac.uk/research/lucky</a>
for further details.</p>

<p><a href="https://i.sstatic.net/GRkWi.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GRkWi.jpg" alt="HST Vs Lucky Imaging"></a></p>

<p>Example 2: <em>HST image of Titan vs an image taken using adaptive optics with the 10m ground-based Keck telescope. Larger aperture wins again because the effects of the atmosphere can be avoided.</em></p>

<p><a href="https://i.sstatic.net/3uFOb.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3uFOb.jpg" alt="HST Vs Keck"></a></p>

CC BY-SA 4.0
2018-10-25T15:51:54.677Z
being in space is good too, the atmosphere diffracts a lot
user24634
CC BY-SA 4.0
2018-10-25T16:20:58.620Z
@user24634 I didn't add that because the issue above trumps it. The issue with the atmosphere is turbulence and actually most of that problem can be removed using clever adaptive optics techniques - but the problem above remains.
ProfRob
CC BY-SA 4.0
2018-10-25T16:39:53.133Z
a Hubble employee mentioning that the atmosphere is the main limitation,
http://www.ucolick.org/~mountain/AAA/aaawiki/doku.php?id=can_we_reveal_the_actual_optical_disk_of_another_star_than_our_sun_s
user24634
CC BY-SA 4.0
2018-10-25T16:41:04.417Z
if the solar corona diffracts light, as it does (no?), how dark would the surrounding region have to be for it to appear bright, from the contrast?
user24634
CC BY-SA 4.0
2018-10-25T16:43:51.103Z
note that larger size of the corona than previously believed. am not 100% on the history of ideas there, exactly how large people have believed it to be prior to this century, perhaps you know more about that?
user24634
CC BY-SA 4.0
2018-10-25T17:52:06.927Z
@user24634 you continue to mis-use the word "diffraction" in many ways.  You will find it a lot easier to learn about optics if you start at the beginning, reading some simple online tutorials or equivalent.
Carl Witthoft
CC BY-SA 4.0
2018-10-25T17:58:49.313Z
there is diffraction in stellar coronas,
https://arxiv.org/abs/1810.06627
user24634
CC BY-SA 4.0
2018-10-25T19:24:55.590Z
@user24634 "Well, it turns out that the real killer **in the past** has not been the size of the mirror but the blurring effects of the atmosphere. " Yep. Not now.
ProfRob
CC BY-SA 4.0
2018-10-25T19:32:53.637Z
@user24634 It is a direct quote from the article you referred to. Don't be absurd.
ProfRob
CC BY-SA 4.0
2018-10-25T23:03:29.947Z
yes from a Hubble employee
user24634
CC BY-SA 4.0
2018-10-25T23:04:00.517Z
the past means before Hubble, they are talking about space based telescopes
user24634
CC BY-SA 4.0
2018-10-25T23:05:38.977Z
here is the hypothesis I've looked at, you can see that it breaks with a few ideas in the consensus model, not too much but a bit. the Voyager 1 image from 1990 fits perfectly with the dimensions of the suns corona (not known at that time) and the distance between the sun and Venus,

https://imgur.com/a/Aggq351
user24634
CC BY-SA 4.0
2018-10-25T23:45:43.837Z
Hey, @user24634, Rob's really trying to help you, and he knows what he's talking about. Please [be open about receiving feedback](https://astronomy.stackexchange.com/conduct), especially when people are putting a lot of their time into trying to help you.
HDE 226868
CC BY-SA 4.0
2018-10-25T15:35:56.457Z
2018-10-25T22:14:24.940Z
2018-10-25T22:14:24.940Z
ProfRob
<p>In the 1700s, Edmond Halley and others discovered that stars appeared larger than they are, and attributed it to diffraction in the lens of an observer (telescope, eye) and/or in the Earth's atmosphere. Are there any ways to view stars without that effect?</p>

CC BY-SA 4.0
2018-10-25T14:57:18.353Z
What kind of answer are you looking for here? There is a physical optics limit that depends on the diameter of the telescope that you can't beat (except by using a bigger telescope or getting nearer to the star).
ProfRob
CC BY-SA 4.0
2018-10-25T14:59:49.450Z
Just the answer to the question. If its no then its no. How I've understood it, turning the brightness down makes it possible to view the actual body of stars, is that true? Could that be used in the context of the question?
user24634
CC BY-SA 4.0
2018-10-25T17:50:58.203Z
Wave diffraction in the telescope is completely different from atmospheric degradations of the wavefront.   What you are asking is unclear.
Carl Witthoft
CC BY-SA 4.0
2018-10-25T19:32:06.363Z
You have no interest in any answers or in learning about anything. You are just here to start arguments. I won't be answering any further questions from you or responding to your comments.
ProfRob
CC BY-SA 4.0
2018-10-25T19:35:39.797Z
no not at all. the atmosphere is a larger barrier. the size of telescopes, that you mentioned, noted that, have taken it to me.
user24634
CC BY-SA 4.0
2018-10-25T20:13:40.563Z
I'm voting to close this question as off-topic because it is evident from your reaction to the (good and deleted) responses from Rob Jeffries (a professional astrophysicist) that you are trolling.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-10-25T20:40:12.447Z
the Voyager 1 image of the sun, Earth and Venus, matches the dimensions of the solar corona, and distance to Venus, 13x the suns diameter (corona width, NASA, 2014) and 77x the suns diameter (sun --> venus)
https://imgur.com/a/7Sqma42
user24634
<star>
Are there any optical method of viewing stars without "diffraction" making them appear larger?
user24634
# Are there any optical method of viewing stars without "diffraction" making them appear larger?

(Asked by: username_0 on 2018-10-25)

In the 1700s, Edmond Halley and others discovered that stars appeared larger than they are, and attributed it to diffraction in the lens of an observer (telescope, eye) and/or in the Earth's atmosphere. Are there any ways to view stars without that effect?

**Tags:** star

> **Comments:**
> **username_1**: What kind of answer are you looking for here? There is a physical optics limit that depends on the diameter of the telescope that you can't beat (except by using a bigger telescope or getting nearer to the star).  
> **username_0**: Just the answer to the question. If its no then its no. How I've understood it, turning the brightness down makes it possible to view the actual body of stars, is that true? Could that be used in the context of the question?  
> **username_2**: Wave diffraction in the telescope is completely different from atmospheric degradations of the wavefront.   What you are asking is unclear.  
> **username_1**: You have no interest in any answers or in learning about anything. You are just here to start arguments. I won't be answering any further questions from you or responding to your comments.  
> **username_0**: no not at all. the atmosphere is a larger barrier. the size of telescopes, that you mentioned, noted that, have taken it to me.  
> **username_3**: I'm voting to close this question as off-topic because it is evident from your reaction to the (good and deleted) responses from Rob Jeffries (a professional astrophysicist) that you are trolling.  
> **username_0**: the Voyager 1 image of the sun, Earth and Venus, matches the dimensions of the solar corona, and distance to Venus, 13x the suns diameter (corona width, NASA, 2014) and 77x the suns diameter (sun --> venus) https://imgur.com/a/7Sqma42  

---

## 1 answers

### Answer by username_1 on 2018-10-25. Score: 3

There is a physical limit to the angular resolution of any imaging system. For a circular aperture it is often quoted that the angular resolution corresponds to around $\theta\_{\rm min} = 1.22 \lambda/D$ (in radians), where $\lambda$ is the wavelength of observation and $D$ is the diameter of the telescope.

A similar limit applies in interferometry but now $D$ might represent the separation between your telescopes.

To translate an angular resolution to an actual physical resolution of size you would have to multiply by the distance to the source.

So the ways in which you can improve matters are:

1. Use a bigger telescope or use an interferometer with a longer baseline.
2. Work at shorter wavelengths.
3. Get closer to the source.

There are of course technical challenges with each of these. In particular you might have thought just increasing the baseline would be easy enough - but you need to know the separation of your telescope to a fraction of the wavelength you are using and that turns out to be tough for larger separations. Shorter wavelengths are problematic for optics - normal lenses and mirrors don't work at X-ray wavelengths for example. Getting closer to the source requires interstellar travel...

The OP wants to argue with me about whether the atmosphere is a significant factor. Of course the atmosphere degrades stellar images (it's not diffraction, but refraction). Going into space overcomes this and **in the past** this **would** have been the limiting issue. However, now it is commonplace for ground-based telescopes to achieve close to their diffraction-limited performance using adaptive optics techniques or "[Lucky Imaging](https://en.m.wikipedia.org/wiki/Lucky_imaging)", both of which can and have got better images than the Hubble Space Telescope (examples below).

Example 1: *The middle picture is from HST, the right hand image is Lucky Imaging from the ground based Palomar 5m telescope. The larger aperture of the Palomar produces better resolution despite looking through the atmosphere.* See <https://www.ast.cam.ac.uk/research/lucky>
for further details.

[![HST Vs Lucky Imaging](https://i.sstatic.net/GRkWi.jpg)](https://i.sstatic.net/GRkWi.jpg)

Example 2: *HST image of Titan vs an image taken using adaptive optics with the 10m ground-based Keck telescope. Larger aperture wins again because the effects of the atmosphere can be avoided.*

[![HST Vs Keck](https://i.sstatic.net/3uFOb.jpg)](https://i.sstatic.net/3uFOb.jpg)

> **Comments:**
> **username_0**: being in space is good too, the atmosphere diffracts a lot  
> **username_1**: @username_0 I didn't add that because the issue above trumps it. The issue with the atmosphere is turbulence and actually most of that problem can be removed using clever adaptive optics techniques - but the problem above remains.  
> **username_0**: a Hubble employee mentioning that the atmosphere is the main limitation, http://www.ucolick.org/~mountain/AAA/aaawiki/doku.php?id=can_we_reveal_the_actual_optical_disk_of_another_star_than_our_sun_s  
> **username_0**: if the solar corona diffracts light, as it does (no?), how dark would the surrounding region have to be for it to appear bright, from the contrast?  
> **username_0**: note that larger size of the corona than previously believed. am not 100% on the history of ideas there, exactly how large people have believed it to be prior to this century, perhaps you know more about that?  
> **username_2**: @username_0 you continue to mis-use the word "diffraction" in many ways.  You will find it a lot easier to learn about optics if you start at the beginning, reading some simple online tutorials or equivalent.  
> **username_0**: there is diffraction in stellar coronas, https://arxiv.org/abs/1810.06627  
> **username_1**: @username_0 "Well, it turns out that the real killer **in the past** has not been the size of the mirror but the blurring effects of the atmosphere. " Yep. Not now.  
> **username_1**: @username_0 It is a direct quote from the article you referred to. Don't be absurd.  
> **username_0**: yes from a Hubble employee  
> **username_0**: the past means before Hubble, they are talking about space based telescopes  
> **username_0**: here is the hypothesis I've looked at, you can see that it breaks with a few ideas in the consensus model, not too much but a bit. the Voyager 1 image from 1990 fits perfectly with the dimensions of the suns corona (not known at that time) and the distance between the sun and Venus,  https://imgur.com/a/Aggq351  
> **username_4**: Hey, @username_0, Rob's really trying to help you, and he knows what he's talking about. Please [be open about receiving feedback](https://astronomy.stackexchange.com/conduct), especially when people are putting a lot of their time into trying to help you.  

---

