<p>What you propose is not impossible, but I think impractical. The levels of contrast required might be 1 part in a billion (<span class="math-container">$10^9$</span>) or more.</p>
<p>In your method, how would you account for non-axisymmetric inhomogeneities of the telescope, which are bound to be bigger than this and quite probably time variable?</p>
<p>Secondly, properly characterising a tiny blip on top of a pedestal of noise is not so easy. Especially when you are using a detector (a CCD camera) with limited dynamic range.</p>
<p>For example, if your analogue-to-digital convertor is 16-bit, then the best you can do is find an excess of 1 count in 65,000 per pixel. But in practice you can't do as well as this because the noise on 65,000 counts will be <span class="math-container">$\sqrt{65000}$</span> (assuming a gain of 1).</p>

CC BY-SA 4.0
2023-03-04T08:59:12.470Z
So if we use a 64bit ADC, and  somehow spin the telescope, it should be doable?
Abdullah is not an Amalekite
CC BY-SA 4.0
2023-03-04T09:23:32.440Z
@Abdullah you'll need to make *coulombs of photoelectrons* (circa $10^{20}$) to push $\sqrt{n}$ down to $10^{-10}$ to get a theoretical signal to noise, but that's just the beginning. Every pixel in a CCD behaves differently, collects a slightly different amount of light, has a different leakage current... it's a huge mess of problems to try to calibrate, and *calibrate how?* Very few things in experimental science can be measured to ten digits of accuracy besides those expressible as times and distances.
uhoh
CC BY-SA 4.0
2023-03-04T07:34:13.060Z
2023-03-04T07:34:13.060Z
ProfRob
<p>My understanding is that the main obsracle to seeing habitable planets is glare. Right now, the best solutions are coronagraphs and proposed starshade satellites which blocks the star.</p>
<p>But is this the only way? We know that the glare is axisymmetric. So we can measure the intensity along a ring centered on the star. The intensity should be the same along all points. Any spike - unless it can be attributed to another star or the telescope - is a planet.</p>

<exoplanet>
Seeing exoplanets with glare
Abdullah is not an Amalekite
# Seeing exoplanets with glare

(Asked by: username_0 on 2023-03-04)

My understanding is that the main obsracle to seeing habitable planets is glare. Right now, the best solutions are coronagraphs and proposed starshade satellites which blocks the star.

But is this the only way? We know that the glare is axisymmetric. So we can measure the intensity along a ring centered on the star. The intensity should be the same along all points. Any spike - unless it can be attributed to another star or the telescope - is a planet.

**Tags:** exoplanet

---

## 1 answers

### Answer by username_1 on 2023-03-04. Score: 4

What you propose is not impossible, but I think impractical. The levels of contrast required might be 1 part in a billion ($10^9$) or more.

In your method, how would you account for non-axisymmetric inhomogeneities of the telescope, which are bound to be bigger than this and quite probably time variable?

Secondly, properly characterising a tiny blip on top of a pedestal of noise is not so easy. Especially when you are using a detector (a CCD camera) with limited dynamic range.

For example, if your analogue-to-digital convertor is 16-bit, then the best you can do is find an excess of 1 count in 65,000 per pixel. But in practice you can't do as well as this because the noise on 65,000 counts will be $\sqrt{65000}$ (assuming a gain of 1).

> **Comments:**
> **username_0**: So if we use a 64bit ADC, and  somehow spin the telescope, it should be doable?  
> **username_2**: @Abdullah you'll need to make *coulombs of photoelectrons* (circa $10^{20}$) to push $\sqrt{n}$ down to $10^{-10}$ to get a theoretical signal to noise, but that's just the beginning. Every pixel in a CCD behaves differently, collects a slightly different amount of light, has a different leakage current... it's a huge mess of problems to try to calibrate, and *calibrate how?* Very few things in experimental science can be measured to ten digits of accuracy besides those expressible as times and distances.  

---

