[gnuastro-commits] master 7d95e33: Link to a amateur image of M51, showing its wings in tutorial

[Mohammad Akhlaghi]

branch: master
commit 7d95e3385289f7bc5f09b76913f302f60cb5b572
Author: Mohammad Akhlaghi <address@hidden>
Commit: Mohammad Akhlaghi <address@hidden>

    Link to a amateur image of M51, showing its wings in tutorial
    
    While I was looking around in Reddit this evening, I came across a very
    nice 12 hour exposure of M51, which clearly shows the very low surface
    brightness signal that is detected in the tutorial, but invisible in the
    input image. So using this other image is a good demonstration of the
    reality of the detection for those who are dubious about the statistics.
---
 doc/gnuastro.texi | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/doc/gnuastro.texi b/doc/gnuastro.texi
index c1d3269..7fcfa34 100644
--- a/doc/gnuastro.texi
+++ b/doc/gnuastro.texi
@@ -4261,6 +4261,15 @@ more than 20 times) than the standard deviation (final 
extension). So we
 can stop configuring NoiseChisel at this point in the tutorial. We leave
 further configuration for a more accurate detection to you as an exercise.
 
+At first sight, this extent may seem too far deep into the noise. Ofcourse,
+there is no way you can visually see extended signal that is has a 0.05
+signal-to-noise ratio. Therefore, if the statistical argument above to
+justify this extent hasn't convinced you, see this amateur astronomer's 12
+hour deep image of this system (and the much wider area around it):
address@hidden://i.redd.it/address@hidden image is taken from
+this Reddit discussion:
address@hidden://www.reddit.com/r/Astronomy/comments/9d6x0q/12_hours_of_exposure_on_the_whirlpool_galaxy/}}.
+
 Let's see how deeply/successfully we carved out M51 and NGC 5195's tail
 from the noise. For this measurement, we'll need to estimate the average
 flux on the outer edges of the detection. Fortunately all this can be done