Hydrogen Alpha region in Cygnus

On Saturday, July 11, 2015 at 11:49:14 AM UTC-5, Uncarollo2 wrote:
On Saturday, July 11, 2015 at 9:20:37 AM UTC-5, Chris L Peterson wrote:
On Fri, 10 Jul 2015 23:09:57 -0700 (PDT), "Chris.B"
wrote:

The tiny stars look very natural and satisfying.
Too many imagers enlarge [or digitally over-process?] to the point where stars become bloated and of equal "size".
The sense of realism [as if seeing the view with the naked eye through a window] simply vanishes.
The same goes for many over-enlarged, planetary images.
Just because they can does not mean that they should.
Naturalness should always be the ultimate goal.IMHO.
To show only how a local observer would/might see the object without optical aid is a real accomplishment.

Well, almost all of these objects (except for the stars) would not be
visible to an observer, local or otherwise. Imaging allows us to see
what we cannot see with our eyes.

And while naturalness is a reasonable goal for an image with a
specific aesthetic intent, there are many imaging and processing
techniques that are better at revealing information. For instance, we
could see more in Roland's and David's images if they utilized a false
color palette. The result would be "unnatural", but could take
advantage of the way our eyes work in order to reveal more detail than
we can see in grayscale. It's a matter of intent.

In the case of the Milky Way H-alpha clouds, the predominant color would be red since almost nothing else is there but hydrogen gas. When we image things like super nova remnants, planetary nebulas, etc. then we see other colors due to the presence of oxygen, sulfur and other elements. We get the color by using narrow band filters which eliminate the background sky glow of our own planet and let us gather the faint photons of these galactic molecules.

UncaNebula

Here is a color image of this area. You can see that there really isn't much there except the red hydrogen clouds, and their intricate shapes are lost:

http://www.skyimager.net/astro/nebul...HaRGB-1007.jpg

On Sat, 11 Jul 2015 09:49:13 -0700 (PDT), Uncarollo2
wrote:

In the case of the Milky Way H-alpha clouds, the predominant color would be red since almost nothing else is there but hydrogen gas.

Of course, that's using "color" in a very casual way, since color is a
physiological phenomenon, not a physical one. We would not perceive
any color with our eyes, no matter how close we might be to these
clouds. Indeed, in most cases, we'd perceive nothing at all. Only the
densest hydrogen clouds would be bright enough to be detected by our
eyes, and those without any sense of color.

On Sat, 11 Jul 2015 11:08:23 -0600, Chris L Peterson
wrote:
On Sat, 11 Jul 2015 09:49:13 -0700 (PDT), Uncarollo2
wrote:

In the case of the Milky Way H-alpha clouds, the predominant color
would be red since almost nothing else is there but hydrogen gas.

Of course, that's using "color" in a very casual way, since color
is a
physiological phenomenon, not a physical one. We would not perceive
any color with our eyes, no matter how close we might be to these
clouds. Indeed, in most cases, we'd perceive nothing at all. Only
the
densest hydrogen clouds would be bright enough to be detected by our
eyes, and those without any sense of color.

Doesn't H-alpha belong to those deep red wavelengths which are
invisible to night (scotopic) vision? Which meant that either our
eyes see H-alpha as deep red, or if it's too faint, our eyes don't
see it at all.

On Sat, 11 Jul 2015 20:28:48 +0200, Paul Schlyter
wrote:

Doesn't H-alpha belong to those deep red wavelengths which are
invisible to night (scotopic) vision? Which meant that either our
eyes see H-alpha as deep red, or if it's too faint, our eyes don't
see it at all.

H-alpha, at 658 nm, is almost exactly at the sensitivity crossover
between the rods and the L cones. The actual perceived color when the
light is very dim seems to vary, and probably depends on secondary
effects as well, such as cell density and the part of the retina being
utilized. Some people do report seeing ionized hydrogen regions as
faintly red, but most seem to report gray.

When I observe 658 nm light from a monochromator, I see it go
colorless before I stop seeing the output at all.

On 11/07/2015 19:44, Chris L Peterson wrote:
On Sat, 11 Jul 2015 20:28:48 +0200, Paul Schlyter
wrote:

Doesn't H-alpha belong to those deep red wavelengths which are
invisible to night (scotopic) vision? Which meant that either our
eyes see H-alpha as deep red, or if it's too faint, our eyes don't
see it at all.

H-alpha, at 658 nm, is almost exactly at the sensitivity crossover
between the rods and the L cones. The actual perceived color when the
light is very dim seems to vary, and probably depends on secondary
effects as well, such as cell density and the part of the retina being
utilized. Some people do report seeing ionized hydrogen regions as
faintly red, but most seem to report gray.

We had some weak largely anecdotal evidence since the sample size was
small that some women could see faint H-alpha as colour red at lower
levels than men. It is known that female colour vision is slightly
superior but the standard tests are on hues in normal lighting. eg

http://jov.arvojournals.org/article....icleid=2191397

When I observe 658 nm light from a monochromator, I see it go
colorless before I stop seeing the output at all.


Same with some near IR LEDs - certainly they don't look red at all.

--
Regards,
Martin Brown

On Monday, July 13, 2015 at 8:45:37 AM UTC-4, Martin Brown wrote:

We had some weak largely anecdotal evidence since the sample size was
small that some women could see faint H-alpha as colour red at lower
levels than men. It is known that female colour vision is slightly
superior but the standard tests are on hues in normal lighting. eg

http://jov.arvojournals.org/article....icleid=2191397

Those sorts of studies are quite suspect.

Note the following:

http://news.bbcimg.co.uk/nol/shared/...dhtml_6_v2.gif

The "brown" square in the center of the top face of the cube is the same color as the "yellow" square in the center of the front face.

The phenomenon is due to lateral inhibition in the retina.

On Mon, 13 Jul 2015 07:15:41 -0700 (PDT), wrote:

On Monday, July 13, 2015 at 8:45:37 AM UTC-4, Martin Brown wrote:

We had some weak largely anecdotal evidence since the sample size was
small that some women could see faint H-alpha as colour red at lower
levels than men. It is known that female colour vision is slightly
superior but the standard tests are on hues in normal lighting. eg

http://jov.arvojournals.org/article....icleid=2191397

Those sorts of studies are quite suspect.

Note the following:

http://news.bbcimg.co.uk/nol/shared/...dhtml_6_v2.gif

The "brown" square in the center of the top face of the cube is the same color as the "yellow" square in the center of the front face.

The phenomenon is due to lateral inhibition in the retina.

How does that make the study (or worse, "those sorts of studies")
suspect? Well constructed studies of visual phenomena include
controls, and take into consideration recognized illusions. Are you
suggesting that the study referenced was of poor quality? In what way?

On 13/07/2015 15:15, wrote:
On Monday, July 13, 2015 at 8:45:37 AM UTC-4, Martin Brown wrote:

We had some weak largely anecdotal evidence since the sample size was
small that some women could see faint H-alpha as colour red at lower
levels than men. It is known that female colour vision is slightly
superior but the standard tests are on hues in normal lighting. eg

http://jov.arvojournals.org/article....icleid=2191397

Those sorts of studies are quite suspect.

Just because you don't want to believe the result?

Do you also deny that colour blindness is sex linked and that the odds
of being colour blind are worse for men XY at 1 in 12. Whereas women XX
get two bites at the cherry for having good colour vision at 1 in 20.

Picking out ripe fruit more clearly has a real survival advantage.

--
Regards,
Martin Brown

On Mon, 13 Jul 2015 17:18:38 +0100, Martin Brown
wrote:

Just because you don't want to believe the result?

Do you also deny that colour blindness is sex linked and that the odds
of being colour blind are worse for men XY at 1 in 12. Whereas women XX
get two bites at the cherry for having good colour vision at 1 in 20.

Because of the way that the genes for our cone pigments are carried on
allosomes, we see other sex-linked visual phenomena as well.
Tetrachromacy is far more common in women, and at least some
tetrachromats show better color discrimination (and wider gamuts) than
normal trichromats.

It would be surprising _not_ to find differences in color vision
between men and women.

On Monday, July 13, 2015 at 12:18:42 PM UTC-4, Martin Brown wrote:
On 13/07/2015 15:15, wsnell01 wrote:
On Monday, July 13, 2015 at 8:45:37 AM UTC-4, Martin Brown wrote:

We had some weak largely anecdotal evidence since the sample size was
small that some women could see faint H-alpha as colour red at lower
levels than men. It is known that female colour vision is slightly
superior but the standard tests are on hues in normal lighting. eg

http://jov.arvojournals.org/article....icleid=2191397

Those sorts of studies are quite suspect.

Just because you don't want to believe the result?

Clearly a better study, having adequate controls, would be needed to make what, in any case, would be a trivial result.

Do you also deny that colour blindness is sex linked and that the odds
of being colour blind are worse for men XY at 1 in 12.

That was an irrelevant comment/question.


Whereas women XX
get two bites at the cherry for having good colour vision at 1 in 20.

That was an irrelevant comment.

Picking out ripe fruit more clearly has a real survival advantage.

Most men, even most color blind ones, should be able to get by, when it comes to picking ripe versus unripe fruit. The differences uncovered are at best trivial. Further, most men have better discrimination than some women, and most women have worse discrimination than some men.

So, were you able to convince yourself that the two squares mentioned in the image are in fact the very same color?