APOD: Hubble's Messier 5 (2017 Nov 04)

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APOD: Hubble's Messier 5 (2017 Nov 04)

Postby APOD Robot » Sat Nov 04, 2017 4:09 am

Image Hubble's Messier 5

Explanation: "Beautiful Nebula discovered between the Balance [Libra] & the Serpent [Serpens] ..." begins the description of the 5th entry in 18th century astronomer Charles Messier's famous catalog of nebulae and star clusters. Though it appeared to Messier to be fuzzy and round and without stars, Messier 5 (M5) is now known to be a globular star cluster, 100,000 stars or more, bound by gravity and packed into a region around 165 light-years in diameter. It lies some 25,000 light-years away. Roaming the halo of our galaxy, globular star clusters are ancient members of the Milky Way. M5 is one of the oldest globulars, its stars estimated to be nearly 13 billion years old. The beautiful star cluster is a popular target for Earthbound telescopes. Of course, deployed in low Earth orbit on April 25, 1990, the Hubble Space Telescope has also captured its own stunning close-up view that spans about 20 light-years across the central region of M5. Even close to its dense core the cluster's aging red and blue giant stars and rejuvenated blue stragglers stand out in yellow and blue hues in the sharp color image.

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 4:36 am

As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

Bruce

P.S. The only thing red in this apod is the distraction spikes on bright yellow stars.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby geckzilla » Sat Nov 04, 2017 6:18 am

BDanielMayfield wrote:As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

Bruce

P.S. The only thing red in this apod is the distraction spikes on bright yellow stars.

A lot of Hubble datasets only cover two lightwave bands. Ergo, the resulting image will range between cyan and orange colored rather than a richer spectrum of colors. Don't blame the processing. Blame the lack of Hubble time available. Although... I will say that globular clusters are pretty much always like this, regardless of the number of bands. They really aren't very colorful. I just realized this one really does have three bands, nonetheless it appears practically two-color.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Boomer12k » Sat Nov 04, 2017 8:31 am

Nice image...

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 10:05 am

geckzilla wrote:
BDanielMayfield wrote:As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

Bruce

P.S. The only thing red in this apod is the distraction spikes on bright yellow stars.

A lot of Hubble datasets only cover two lightwave bands. Ergo, the resulting image will range between cyan and orange colored rather than a richer spectrum of colors. Don't blame the processing. Blame the lack of Hubble time available. Although... I will say that globular clusters are pretty much always like this, regardless of the number of bands. They really aren't very colorful. I just realized this one really does have three bands, nonetheless it appears practically two-color.

Ok geck. I do respect your expert testimony on this. And, as Boomer said, it is a nice image. It's just a matter of individual tastes as to color preference mixed with a desire to see things in a closer to "true color" format. I like my Red Giants to be red, that's all. I realize that infrared is invisible to us, so any image that converts it into a color we can see isn't really "true", but I still would have liked the red to be stronger here. Ann will likely say the same about blue.

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby neufer » Sat Nov 04, 2017 10:36 am

geckzilla wrote:
BDanielMayfield wrote:
As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

A lot of Hubble datasets only cover two lightwave bands. Ergo, the resulting image will range between cyan and orange colored rather than a richer spectrum of colors. Don't blame the processing. Blame the lack of Hubble time available. Although... I will say that globular clusters are pretty much always like this, regardless of the number of bands. They really aren't very colorful. I just realized this one really does have three bands, nonetheless it appears practically two-color.

Also... our eyes are just more sensitive to blue light.

One needs carbon to scatter the blue light
in order to really appreciate a red star:

http://oneminuteastronomer.com/1206/vampire-star/
http://www.skyandtelescope.com/observin ... 203201401/
Art Neuendorffer

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 11:32 am

neufer wrote:
geckzilla wrote:
BDanielMayfield wrote:
As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

A lot of Hubble datasets only cover two lightwave bands. Ergo, the resulting image will range between cyan and orange colored rather than a richer spectrum of colors. Don't blame the processing. Blame the lack of Hubble time available. Although... I will say that globular clusters are pretty much always like this, regardless of the number of bands. They really aren't very colorful. I just realized this one really does have three bands, nonetheless it appears practically two-color.

Also... our eyes are just more sensitive to blue light.

One needs carbon to scatter the blue light
in order to really appreciate a red star:

http://oneminuteastronomer.com/1206/vampire-star/
http://www.skyandtelescope.com/observin ... 203201401/

Nice points Art. Wouldn't you think though, that in this set of 100,000+ geriatric gems there would be at least a few fat, wheezing old gezzers choking on their own crud? (No offense intended.) :wink:

Bruce
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby heehaw » Sat Nov 04, 2017 11:50 am

Someone please tell me why globular clusters do not contain any significant amount of dark matter. Everything else does.

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby NoelC » Sat Nov 04, 2017 11:54 am

This is a false color image where the blue channel was indeed photographed through a blue filter, but the green channel is really red data and the red channel is infrared data.

Photography specifics here: https://www.spacetelescope.org/images/potw1118a/

Also, the Hubble itself was apparently rotated when shooting the infrared data (shown as the red channel) as compared to the blue and red data (shown as blue and green channels) since we can see that the red diffraction spikes don't align with the blue and green ones. Some elbow grease could correct that by removing the optical spikes, or by removing just the red ones and regenerating equivalent spikes with the same rotation as the blue/green channels.

Lastly, the three color channels are not very well aligned with one another, as you can see red/cyan fringes on virtually every star.

-Noel

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 12:08 pm

heehaw wrote:Someone please tell me why globular clusters do not contain any significant amount of dark matter. Everything else does.

How much of your personal mass is dark matter? Astronomically, how much of the Earth, Sun, etc. is dark matter?

Dark matter just ain't into us baryonic things. The attraction isn't mutual.

Bruce
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 12:11 pm

NoelC wrote:This is a false color image where the blue channel was indeed photographed through a blue filter, but the green channel is really red data and the red channel is infrared data.

Photography specifics here: https://www.spacetelescope.org/images/potw1118a/

Also, the Hubble itself was apparently rotated when shooting the infrared data (shown as the red channel) as compared to the blue and red data (shown as blue and green channels) since we can see that the red diffraction spikes don't align with the blue and green ones. Some elbow grease could correct that by removing the optical spikes, or by removing just the red ones and regenerating equivalent spikes with the same rotation as the blue/green channels.

Lastly, the three color channels are not very well aligned with one another, as you can see red/cyan fringes on virtually every star.

-Noel


Nice explanation Noel. I knew something was off about it.

Bruce
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heehaw

Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby heehaw » Sat Nov 04, 2017 12:18 pm

BDanielMayfield wrote:
heehaw wrote:Someone please tell me why globular clusters do not contain any significant amount of dark matter. Everything else does.

How much of your personal mass is dark matter? Astronomically, how much of the Earth, Sun, etc. is dark matter?

Dark matter just ain't into us baryonic things. The attraction isn't mutual.

Bruce

Thanks, Bruce, but all galaxies, including small ones (indeed, especially small ones) DO contain dark matter. But I have the impression that NO globular cluster does, and I've never read any speculation anywhere as to why that is. It does seem to me to be a very peculiar mystery.

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 12:36 pm

After looking at the specifics that Noel provided here: https://www.spacetelescope.org/images/potw1118a/
I would love to see what this cluster would look like if someone could redo M5 using the blue data for blue, an average of the blue and red channels for green, and an average of the red and infrared channels for red. That might really make the red pop!

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby BDanielMayfield » Sat Nov 04, 2017 12:53 pm

heehaw wrote:
BDanielMayfield wrote:
heehaw wrote:Someone please tell me why globular clusters do not contain any significant amount of dark matter. Everything else does.

How much of your personal mass is dark matter? Astronomically, how much of the Earth, Sun, etc. is dark matter?

Dark matter just ain't into us baryonic things. The attraction isn't mutual.

Bruce

Thanks, Bruce, but all galaxies, including small ones (indeed, especially small ones) DO contain dark matter. But I have the impression that NO globular cluster does, and I've never read any speculation anywhere as to why that is. It does seem to me to be a very peculiar mystery.


Your comment makes sense now that I know the scale of what you where referring to. We do know that dark and normal matter in galactic clusters can become decoupled, as in the Bullet Cluster. Wild speculation here, but perhaps dark matter did have some role in the formation of globulars in the distant past, but passages through denser parts of galaxies during globular cluster orbits decouple the DM?
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Chris Peterson » Sat Nov 04, 2017 2:07 pm

heehaw wrote:
BDanielMayfield wrote:
heehaw wrote:Someone please tell me why globular clusters do not contain any significant amount of dark matter. Everything else does.

How much of your personal mass is dark matter? Astronomically, how much of the Earth, Sun, etc. is dark matter?

Dark matter just ain't into us baryonic things. The attraction isn't mutual.

Bruce

Thanks, Bruce, but all galaxies, including small ones (indeed, especially small ones) DO contain dark matter. But I have the impression that NO globular cluster does, and I've never read any speculation anywhere as to why that is. It does seem to me to be a very peculiar mystery.

There are globular clusters which are suspected to contain small amounts of dark matter (<10% of the mass), and there are globular clusters around other galaxies which appear to have high dark matter content. Whether this difference from the local globulars (that appear to have little or no dark matter) represents a difference in formation history or is a consequence of evolution (such as stripping by galactic tides) remains an area of study.
Chris

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Chris Peterson » Sat Nov 04, 2017 2:16 pm

BDanielMayfield wrote:As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

Aside from all the issues discussed about the filters that have been used and the way two-channel data is processed, the reality is that the coolest red giants that we see are orange-yellow. I'm not aware of any stars we can see that are cool enough to appear red. The only truly red stars are that way because of intervening material altering their color- either in dust clouds or their own atmospheres.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby geckzilla » Sat Nov 04, 2017 2:19 pm

NoelC wrote:This is a false color image where the blue channel was indeed photographed through a blue filter, but the green channel is really red data and the red channel is infrared data.

Photography specifics here: https://www.spacetelescope.org/images/potw1118a/

Also, the Hubble itself was apparently rotated when shooting the infrared data (shown as the red channel) as compared to the blue and red data (shown as blue and green channels) since we can see that the red diffraction spikes don't align with the blue and green ones. Some elbow grease could correct that by removing the optical spikes, or by removing just the red ones and regenerating equivalent spikes with the same rotation as the blue/green channels.

Lastly, the three color channels are not very well aligned with one another, as you can see red/cyan fringes on virtually every star.

It would make very little difference if the red channel was a real red or the near-infrared channel that was used in this case. That only makes a big difference for galaxies, where an image like this would have green ionized hydrogen clouds instead of the preferable pinkish ones, and more background galaxies would be revealed. In this case, the infrared actually helps separate the colors more. If you wanted the globular to become very red, then you would have to include some near-UV data for the blue channel. That would turn the entire globular yellow, and then the most yellowish stars would become red.

As a side note of possible interest, here* are some clusters I picked out from a near-uv / visible blue image of the Triangulum galaxy. Note the distinct difference between a globular cluster and the young ones. The globulars nearly became invisible!
https://twitter.com/SpaceGeck/status/925233406455070723

Regarding the alignment of the channels: I just want to note that even if you align them perfectly, the detector is more sensitive to the redder wavelengths than it is the bluer ones, and the point spread function is also different for each quadrant of the detector. This is close to perfectly aligned, but maybe not exactly. But I'm saying even if it was perfectly aligned, fringing is almost inevitable as the red will spread out a bit farther, and it spreads with some asymmetry. Ergo: colorful fringing.

BDanielMayfield wrote:After looking at the specifics that Noel provided here: https://www.spacetelescope.org/images/potw1118a/
I would love to see what this cluster would look like if someone could redo M5 using the blue data for blue, an average of the blue and red channels for green, and an average of the red and infrared channels for red. That might really make the red pop!

See my reply to Noel. You have the right idea, but you compressed the spectrum in a way that would result in less color separation, not more. Just to reiterate, the F814W filter is very close to human visible red in terms of space images, at least as far as stars go. It reveals some dust-obscured stars and background galaxies, and that's about it.



*Yes, I did mess up that lower right one. Noting it here again in case the tweet below which mentions this is not read. The lower right one is a hydrogen cloud. My bad!
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby neufer » Sat Nov 04, 2017 2:37 pm

Chris Peterson wrote:
There are globular clusters which are suspected to contain small amounts of dark matter (<10% of the mass), and there are globular clusters around other galaxies which appear to have high dark matter content. Whether this difference from the local globulars (that appear to have little or no dark matter) represents a difference in formation history or is a consequence of evolution (such as stripping by galactic tides) remains an area of study.
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<<Dark globular cluster is a proposed type of globular star clusters that has an unusually high mass for the number of stars within it. Proposed in 2015 on the basis of observational data, dark globular clusters are believed to be populated by objects with significant dark matter components, such as central massive black holes. The observational data for dark globular clusters comes from the Very Large Telescope (VLT) in Chile which observed the vicinity of the galaxy Centaurus A. Many of the globular clusters inside that galaxy are brighter and more massive than those orbiting the Milky Way and a sample of 125 globular clusters around Centaurus A was studied using the VLT's FLAMES instrument. While globular clusters are normally considered to be almost devoid of dark matter, the study of the dynamical properties of sampled clusters suggested the presence of exotically concentrated dark matter. The study was published in The Astrophysical Journal. The existence of dark globular clusters would suggest that their formation and evolution are markedly different from other globular clusters in Centaurus A and the Local Group.>>
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby neufer » Sat Nov 04, 2017 4:04 pm

BDanielMayfield wrote:
neufer wrote:
... our eyes are just more sensitive to blue light.

One needs carbon to scatter the blue light
in order to really appreciate a red star:

http://oneminuteastronomer.com/1206/vampire-star/
http://www.skyandtelescope.com/observin ... 203201401/

Nice points Art. Wouldn't you think though, that in this set of 100,000+ geriatric gems there would be at least a few fat, wheezing old gezzers choking on their own crud? (No offense intended.) :wink:
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Chris Peterson » Sat Nov 04, 2017 4:22 pm

neufer wrote:Also... our eyes are just more sensitive to blue light.

Our eyes are least sensitive to blue light. Our short wavelength cone response is one to two orders of magnitude less sensitive than our long wavelength cone response.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby geckzilla » Sat Nov 04, 2017 4:43 pm

Chris Peterson wrote:
neufer wrote:Also... our eyes are just more sensitive to blue light.

Our eyes are least sensitive to blue light. Our short wavelength cone response is one to two orders of magnitude less sensitive than our long wavelength cone response.

This is a very useful fact that is easily observed by hiding various things in the blue channel. At some point I hid some words in an image that said "Write yes in the comments if you can read this." or something like that, and no one wrote yes. I am also thankful for this because the blue channel tends to have the lowest signal to noise ratio and relatively lower in quality.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Chris Peterson » Sat Nov 04, 2017 4:50 pm

geckzilla wrote:
Chris Peterson wrote:
neufer wrote:Also... our eyes are just more sensitive to blue light.

Our eyes are least sensitive to blue light. Our short wavelength cone response is one to two orders of magnitude less sensitive than our long wavelength cone response.

This is a very useful fact that is easily observed by hiding various things in the blue channel. At some point I hid some words in an image that said "Write yes in the comments if you can read this." or something like that, and no one wrote yes. I am also thankful for this because the blue channel tends to have the lowest signal to noise ratio and relatively lower in quality.

Another factor to consider is that the cone density of short wavelength cells is also lowest. Our blue sensitivity isn't just poor, so is our blue resolution. This is very easily seen if you're out at night and observe a commercial sign with illuminated blue letters against a dark background. The writing will look out of focus. But it's not a focus problem; the failure is happening in the retina itself.
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby neufer » Sat Nov 04, 2017 5:31 pm

Chris Peterson wrote:
neufer wrote:
Also... our eyes are just more sensitive to blue light.

Our eyes are least sensitive to blue light. Our short wavelength cone response is one to two orders of magnitude less sensitive than our long wavelength cone response.

Another factor to consider is that the cone density of short wavelength cells is also lowest. Our blue sensitivity isn't just poor, so is our blue resolution. This is very easily seen if you're out at night and observe a commercial sign with illuminated blue letters against a dark background. The writing will look out of focus. But it's not a focus problem; the failure is happening in the retina itself.

While it is true that we have many more orange sensitive L cones & green sensitive M cones than blue sensitive S cones
...we have about 15 times as many green-blue sensitive rod cells as all our own cone cells.

    A rod cell is sensitive enough to respond to a single photon of light
    and is about 100 times more sensitive to a single photon than cones.
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<<Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 90 million rod cells in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is one of the main reasons why colors are much less apparent in darkness.

A rod cell is sensitive enough to respond to a single photon of light and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity (or image resolution) because the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually.

Rod cells also respond slower to light than cones and the stimuli they receive are added over roughly 100 milliseconds. While this makes rods more sensitive to smaller amounts of light, it also means that their ability to sense temporal changes, such as quickly changing images, is less accurate than that of cones.

Experiments by George Wald and others showed that rods are most sensitive to wavelengths of light around 498 nm (green-blue), and insensitive to wavelengths longer than about 640 nm (red). This is responsible for the Purkinje effect: as intensity dims at twilight, the rods take over, and before color disappears completely, peak sensitivity of vision shifts towards the rods' peak sensitivity (blue-green).

Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the sclera. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 100 million rod cells compared to 7 million cone cells.>>
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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby Ann » Sat Nov 04, 2017 5:35 pm

BDanielMayfield wrote:As I see no truly red stars here I take it that the red giants are really yellow? Or is this a processing effect? If so, though it will doubtless be very attractive to many, I say :thumb_down: on the processing. (I like red, almost as much as Ann likes blue.)

Bruce

P.S. The only thing red in this apod is the distraction spikes on bright yellow stars.


Right you are, Bruce. Extremely few stars are red. T Lyrae is red, as is V Aquilae. The latter is the only star that I have observed myself which was really, staggeringly red.

But other supposedly "red" stars turned out to be merely a pale shade of orange, like Mu Cephei.

In my humble opinion, most "red" stars are "less red" than the bluest stars are blue-white. Whatever that means. Surely most cool stars are more yellow than most hot stars are blue.

But even I must admit that when it comes to saturated hues, nothing beats T Lyrae and V Aquilae.

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Re: APOD: Hubble's Messier 5 (2017 Nov 04)

Postby neufer » Sat Nov 04, 2017 5:47 pm

geckzilla wrote:
At some point I hid some [blue] words in an image that said
"Write yes in the comments if you can read this."
or something like that, and no one wrote yes.

    The Asterisk automatically deletes [blue] words.
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<<Anecdotal evidence is evidence from anecdotes, i.e., evidence collected in a casual or informal manner and relying heavily or entirely on personal testimony. Where only one or a few anecdotes are presented, there is a larger chance that they may be unreliable due to cherry-picked or otherwise non-representative samples of typical cases. Similarly, psychologists have found that due to cognitive bias people are more likely to remember notable or unusual examples rather than typical examples. Thus, even when accurate, anecdotal evidence is not necessarily representative of a typical experience. Accurate determination of whether an anecdote is "typical" requires statistical evidence.>>
geckzilla wrote:
... the blue channel tends to have the lowest signal to noise ratio and relatively lower in quality.

Huh :!: :?:
Last edited by neufer on Sat Nov 04, 2017 5:51 pm, edited 1 time in total.
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