Starship Asterisk*

Posted: **Sat Mar 18, 2023 4:06 am**

Wolf-Rayet 124

Explanation: Driven by powerful stellar winds, expanding shrouds of gas and dust frame hot, luminous star Wolf-Rayet 124 in this sharp infrared view. The eye-catching 6-spike star pattern is characteristic of stellar images made with the 18 hexagonal mirrors of the James Webb Space Telescope. About 15,000 light-years distant toward the pointed northern constellation Sagitta, WR 124 has over 30 times the mass of the Sun. Produced in a brief and rarely spotted phase of massive star evolution in the Milky Way, this star's turbulent nebula is nearly 6 light-years across. It heralds WR 124's impending stellar death in a supernova explosion. Formed in the expanding nebula, dusty interstellar debris that survives the supernova will influence the formation of future generations of stars.

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Posted: **Sat Mar 18, 2023 4:14 am**

I'm not a big fan of the 18-mirror diffraction artifact.
But a lovely picture nonetheless

Posted: **Sat Mar 18, 2023 4:56 am**

I was in nuclear medicine for 25 years. Our cameras have no mirrors (or lenses, unless you count lead collimation), but we regularly see six-sided diffraction spikes in the images when the detectors are over-saturated. Is there something about JWST that dictates the six-sided spikes or is it just the degree of over-saturation that makes it 6 and not 4 or 8? I guess since the septa in the nuclear medicine collimators are hexagonal that might make the spikes six-sided, but there are literally thousands in one FOV, so maybe not.

Posted: **Sat Mar 18, 2023 7:47 am**

At the very top left there is a funny galaxy which looks like the empty set in math.

Alex.

Posted: **Sat Mar 18, 2023 8:47 am**

alex555 wrote: ↑Sat Mar 18, 2023 7:47 am At the very top left there is a funny galaxy which looks like the empty set in math.

Alex.

is it that the galaxy is gravi-lensing and representing twice a background quasar?

: Wolf-Rayet 124 (2023 Mar 18).jpg (14.69 KiB) Viewed 4043 times

Posted: **Sat Mar 18, 2023 8:58 am**

I would never thought of such colour representation but why not?
The stars are in the near infrared only, so they are represented truly.

This image combines various filters from both Webb imaging instruments, with the color red assigned to wavelengths of 4.44, 4.7, 12.8, and 18 microns (F444W, F470N, F1280W, F1800W), green to 2.1, 3.35, and 11.3 microns (F210M, F335M, F1130W), and blue to 0.9, 1.5, and 7.7 microns (F090W, F150W, F770W).

But what about the IR colour of the Empty Set Galaxy?
Well, it is not in the MIRI's frame, so it's orange comes from 2.1, 3.35, 4.44, 4.7 microns

Posted: **Sat Mar 18, 2023 8:59 am**

alex555 wrote: ↑Sat Mar 18, 2023 7:47 am At the very top left there is a funny galaxy which looks like the empty set in math.

Alex.

: Null sign or Danish letter Ø detail from APOD 18 March 2023.png (50.96 KiB) Viewed 4039 times

This galaxy looks like the null sign, you mean? This?

∅

Or maybe it is a Danish letter? You know that Copenhagen, the capital of Denmark, is spelled "København" in Danish?

Sorry for exaggerating the ø!

Ann

Posted: **Sat Mar 18, 2023 9:06 am**

Ann wrote: ↑Sat Mar 18, 2023 8:59 am
alex555 wrote: ↑Sat Mar 18, 2023 7:47 am At the very top left there is a funny galaxy which looks like the empty set in math.

Alex.

Null sign or Danish letter Ø detail from APOD 18 March 2023.png

This galaxy looks like the null sign, you mean? This? ∅

Or maybe it is a Danish letter? You know that Copenhagen, the capital of Denmark, is spelled "København" in Danish?

Sorry for exaggerating the ø!

Ann

Are they really different symbols?
empty set (U+2205) ∅
diameter sign (U+2300) ⌀
latin capital letter o with stroke (U+00D8) Ø

Posted: **Sat Mar 18, 2023 9:08 am**

I, too, find the diffraction spikes visually disturbing, but the purpose of Webb is not to produce aestetically pleasing images.
Note that there are eight spikes, six originating from the hexagonal mirrors and two more ("horizontal") from the three spokes carrying the secondary mirror.
The following illustration from https://bigthink.com/starts-with-a-bang ... bb-spikes/ might be helpful:

It is the "vertical" spoke which produces the "horisontal" spikes. The other two spokes also produce spikes, but they overlap those produced by the mirrors. As a non-English speaker I hope that "spoke" is the correct term

(This should be a high-resolution image, but I can't figure out how to enlarge it on this page)

Posted: **Sat Mar 18, 2023 9:19 am**

I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?

Posted: **Sat Mar 18, 2023 11:03 am**

VictorBorun wrote: ↑Sat Mar 18, 2023 9:06 am
Ann wrote: ↑Sat Mar 18, 2023 8:59 am
alex555 wrote: ↑Sat Mar 18, 2023 7:47 am At the very top left there is a funny galaxy which looks like the empty set in math.

Alex.

Null sign or Danish letter Ø detail from APOD 18 March 2023.png

This galaxy looks like the null sign, you mean? This? ∅

Or maybe it is a Danish letter? You know that Copenhagen, the capital of Denmark, is spelled "København" in Danish?

Sorry for exaggerating the ø!

Ann
Are they really different symbols?
empty set (U+2205) ∅

You are right, they are different. And sorry for sort of messing up what you wrote in my reply.

Ann

Posted: **Sat Mar 18, 2023 11:05 am**

VictorBorun wrote: ↑Sat Mar 18, 2023 9:19 am I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?

In my opinion, it is virtually impossible for the nebula of WR 124 to be two dimensional. It has to be more or less spherical, or possibly two-lobed, in such a way that we are watching one of the lobes face on.

Ann

Posted: **Sat Mar 18, 2023 2:12 pm**

eljayhalflife wrote: ↑Sat Mar 18, 2023 4:56 am I was in nuclear medicine for 25 years. Our cameras have no mirrors (or lenses, unless you count lead collimation), but we regularly see six-sided diffraction spikes in the images when the detectors are over-saturated. Is there something about JWST that dictates the six-sided spikes or is it just the degree of over-saturation that makes it 6 and not 4 or 8? I guess since the septa in the nuclear medicine collimators are hexagonal that might make the spikes six-sided, but there are literally thousands in one FOV, so maybe not.

It is precisely because gamma ray collimators have hexagonal cells that you see hexagonal diffraction spikes in gamma ray imagery. It does not matter whether you have a single hexagonal aperture, 18 hexagonal apertures, or a thousand hexagonal aperture. Other than the amount of energy that ends up in the diffraction spikes, the geometry of those spikes will be the same.

Posted: **Sat Mar 18, 2023 2:13 pm**

Ann wrote: ↑Sat Mar 18, 2023 11:05 am
VictorBorun wrote: ↑Sat Mar 18, 2023 9:19 am I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?
In my opinion, it is virtually impossible for the nebula of WR 124 to be two dimensional. It has to be more or less spherical, or possibly two-lobed, in such a way that we are watching one of the lobes face on.

Ann

The scientific term for the sort of shapes you're trying to describe is "blobby". (And I agree with your assessment.)

Posted: **Sat Mar 18, 2023 2:16 pm**

Ann wrote: ↑Sat Mar 18, 2023 11:03 am
VictorBorun wrote: ↑Sat Mar 18, 2023 9:06 am
Ann wrote: ↑Sat Mar 18, 2023 8:59 am

Null sign or Danish letter Ø detail from APOD 18 March 2023.png

This galaxy looks like the null sign, you mean? This? :arrow: ∅

Or maybe it is a Danish letter? You know that Copenhagen, the capital of Denmark, is spelled "København" in Danish?

Sorry for exaggerating the ø!

Ann
Are they really different symbols?
empty set (U+2205) ∅

You are right, they are different.

Ann
diameter sign (U+2300) ⌀
latin capital letter o with stroke (U+00D8) Ø

In terms of physical font, they may well be graphically identical. In terms of logical characters, they are defined differently, which makes sense when you consider things like screen readers for the blind or network scanners constructing search indexes.

Posted: **Sat Mar 18, 2023 3:18 pm**

VictorBorun wrote: ↑Sat Mar 18, 2023 9:19 am I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?

Line of sight is discussed in the " frame" link for Wolf-Rayet (WR) nebula M 1-67.

Posted: **Sat Mar 18, 2023 4:23 pm**

Chris Peterson wrote: ↑Sat Mar 18, 2023 2:12 pm
eljayhalflife wrote: ↑Sat Mar 18, 2023 4:56 am I was in nuclear medicine for 25 years. Our cameras have no mirrors (or lenses, unless you count lead collimation), but we regularly see six-sided diffraction spikes in the images when the detectors are over-saturated. Is there something about JWST that dictates the six-sided spikes or is it just the degree of over-saturation that makes it 6 and not 4 or 8? I guess since the septa in the nuclear medicine collimators are hexagonal that might make the spikes six-sided, but there are literally thousands in one FOV, so maybe not.
It is precisely because gamma ray collimators have hexagonal cells that you see hexagonal diffraction spikes in gamma ray imagery. It does not matter whether you have a single hexagonal aperture, 18 hexagonal apertures, or a thousand hexagonal aperture. Other than the amount of energy that ends up in the diffraction spikes, the geometry of those spikes will be the same.

Thanks, Chris. The science/math part of my brain said that, but then I doubted myself because of the size of the individual units in the collimator "honeycomb" and quantity of the cells. But what gives JWST 6-sided spikes? One would think 8 or 16 because of the 16 mirrors.

Posted: **Sat Mar 18, 2023 4:34 pm**

eljayhalflife wrote: ↑Sat Mar 18, 2023 4:23 pm
Chris Peterson wrote: ↑Sat Mar 18, 2023 2:12 pm
eljayhalflife wrote: ↑Sat Mar 18, 2023 4:56 am I was in nuclear medicine for 25 years. Our cameras have no mirrors (or lenses, unless you count lead collimation), but we regularly see six-sided diffraction spikes in the images when the detectors are over-saturated. Is there something about JWST that dictates the six-sided spikes or is it just the degree of over-saturation that makes it 6 and not 4 or 8? I guess since the septa in the nuclear medicine collimators are hexagonal that might make the spikes six-sided, but there are literally thousands in one FOV, so maybe not.
It is precisely because gamma ray collimators have hexagonal cells that you see hexagonal diffraction spikes in gamma ray imagery. It does not matter whether you have a single hexagonal aperture, 18 hexagonal apertures, or a thousand hexagonal aperture. Other than the amount of energy that ends up in the diffraction spikes, the geometry of those spikes will be the same.
Thanks, Chris. The science/math part of my brain said that, but then I doubted myself because of the size of the individual units in the collimator "honeycomb" and quantity of the cells. But what gives JWST 6-sided spikes? Is it a function of the 18 mirrors /3?.

Posted: **Sat Mar 18, 2023 4:48 pm**

Chris Peterson wrote: ↑Sat Mar 18, 2023 2:16 pm
Ann wrote: ↑Sat Mar 18, 2023 11:03 am
VictorBorun wrote: ↑Sat Mar 18, 2023 9:06 am

Are they really different symbols?
empty set (U+2205) ∅

You are right, they are different.

Ann
diameter sign (U+2300) ⌀
latin capital letter o with stroke (U+00D8) Ø

In terms of physical font, they may well be graphically identical. In terms of logical characters, they are defined differently, which makes sense when you consider things like screen readers for the blind or network scanners constructing search indexes.

In physical terms the Einstein ring here is round while the letter Ø has height > width
Diameter sign ⌀ and empty set ∅ are harder to tell apart.
Is it just me or does the galaxy disk extend more 1 o'clock than 7 o'clock from its core?
Then again there is light pollution from the foreground stars eating the 7 o'clock part.
Suggesting greek letters Φϕ … oh no, those, too, can be equitailed

On the second look there seems to be a black foreground line crossing the Einstein ring along the galaxy disk… Or is the galaxy disk in fact just a gravi-lens artifact?

Posted: **Sat Mar 18, 2023 5:54 pm**

APOD Robot wrote: ↑Sat Mar 18, 2023 4:06 am Wolf-Rayet 124

I also like geck's version

biggg:https://live.staticflickr.com/65535/527 ... 8fae_o.png
Credit: NASA/ESA/CSA/ Judy Schmidt

Comment "This version of WR 124 is a combination of Hubble and JWST MIRI data. A press release recently featured the same data, and since this is one of my favorite objects, of course I had to have a go at it. The official release from the ERO team was a little bit dark. I also went ahead and used the same G'MIC processing to remove much of the banding noise from the dark parts of the image, allowing me to make it even brighter."

Red: JWST/MIRI F1800W
Yellow: JWST/MIRI F1280W
Yellow-Green: JWST/MIRI F1130W
Cyan: JWST/MIRI F770W
Blue: HST WF/PC2 F656N

Posted: **Sat Mar 18, 2023 7:06 pm**

VictorBorun wrote: ↑Sat Mar 18, 2023 4:48 pm
Chris Peterson wrote: ↑Sat Mar 18, 2023 2:16 pm
In terms of physical font, they may well be graphically identical. In terms of logical characters, they are defined differently, which makes sense when you consider things like screen readers for the blind or network scanners constructing search indexes.
In physical terms the Einstein ring here is round while the letter Ø has height > width
Diameter sign ⌀ and empty set ∅ are harder to tell apart.
Is it just me or does the galaxy disk extend more 1 o'clock than 7 o'clock from its core?
Then again there is light pollution from the foreground stars eating the 7 o'clock part.
Suggesting greek letters Φϕ … oh no, those, too, can be equitailed

Any of these characters can have any aspect ratio, tall, wide, whatever. That's a decision by the font designer, not something intrinsic to the logical character in any way. They can be graphically identical to each other, or designed to look very different. A matter of aesthetics only.

Posted: **Sat Mar 18, 2023 7:13 pm**

eljayhalflife wrote: ↑Sat Mar 18, 2023 4:23 pm
Chris Peterson wrote: ↑Sat Mar 18, 2023 2:12 pm
eljayhalflife wrote: ↑Sat Mar 18, 2023 4:56 am I was in nuclear medicine for 25 years. Our cameras have no mirrors (or lenses, unless you count lead collimation), but we regularly see six-sided diffraction spikes in the images when the detectors are over-saturated. Is there something about JWST that dictates the six-sided spikes or is it just the degree of over-saturation that makes it 6 and not 4 or 8? I guess since the septa in the nuclear medicine collimators are hexagonal that might make the spikes six-sided, but there are literally thousands in one FOV, so maybe not.
It is precisely because gamma ray collimators have hexagonal cells that you see hexagonal diffraction spikes in gamma ray imagery. It does not matter whether you have a single hexagonal aperture, 18 hexagonal apertures, or a thousand hexagonal aperture. Other than the amount of energy that ends up in the diffraction spikes, the geometry of those spikes will be the same.
Thanks, Chris. The science/math part of my brain said that, but then I doubted myself because of the size of the individual units in the collimator "honeycomb" and quantity of the cells. But what gives JWST 6-sided spikes? One would think 8 or 16 because of the 16 mirrors.

Diffraction is produced by edges. A circular aperture produces a diffraction pattern made up of rings around bright sources. Straight edges produce lines that are perpendicular to the angle of the edge. It doesn't matter how many edges there are, only how many different angles there are. Whether you have a single hexagonal aperture, or 18 edge-aligned hexagons, or a 1000 hole honeycomb, there are only six angles, meaning only six diffraction spikes. (Actually, each edge produces a pair of spikes, one in each direction, so six edge directions produces 12 spikes... but since they overlap each other, we only see 6.)

Posted: **Sat Mar 18, 2023 10:33 pm**

Chris Peterson wrote: ↑Sat Mar 18, 2023 7:13 pm
eljayhalflife wrote: ↑Sat Mar 18, 2023 4:23 pm
Chris Peterson wrote: ↑Sat Mar 18, 2023 2:12 pm

It is precisely because gamma ray collimators have hexagonal cells that you see hexagonal diffraction spikes in gamma ray imagery. It does not matter whether you have a single hexagonal aperture, 18 hexagonal apertures, or a thousand hexagonal aperture. Other than the amount of energy that ends up in the diffraction spikes, the geometry of those spikes will be the same.
Thanks, Chris. The science/math part of my brain said that, but then I doubted myself because of the size of the individual units in the collimator "honeycomb" and quantity of the cells. But what gives JWST 6-sided spikes? One would think 8 or 16 because of the 16 mirrors.
Diffraction is produced by edges. A circular aperture produces a diffraction pattern made up of rings around bright sources. Straight edges produce lines that are perpendicular to the angle of the edge. It doesn't matter how many edges there are, only how many different angles there are. Whether you have a single hexagonal aperture, or 18 edge-aligned hexagons, or a 1000 hole honeycomb, there are only six angles, meaning only six diffraction spikes. (Actually, each edge produces a pair of spikes, one in each direction, so six edge directions produces 12 spikes... but since they overlap each other, we only see 6.)

what, a 7-gonal mirror would give 14 spikes to a bright star?

Posted: **Sun Mar 19, 2023 1:47 am**

VictorBorun wrote: ↑Sat Mar 18, 2023 10:33 pm
Chris Peterson wrote: ↑Sat Mar 18, 2023 7:13 pm
eljayhalflife wrote: ↑Sat Mar 18, 2023 4:23 pm

Thanks, Chris. The science/math part of my brain said that, but then I doubted myself because of the size of the individual units in the collimator "honeycomb" and quantity of the cells. But what gives JWST 6-sided spikes? One would think 8 or 16 because of the 16 mirrors.
Diffraction is produced by edges. A circular aperture produces a diffraction pattern made up of rings around bright sources. Straight edges produce lines that are perpendicular to the angle of the edge. It doesn't matter how many edges there are, only how many different angles there are. Whether you have a single hexagonal aperture, or 18 edge-aligned hexagons, or a 1000 hole honeycomb, there are only six angles, meaning only six diffraction spikes. (Actually, each edge produces a pair of spikes, one in each direction, so six edge directions produces 12 spikes... but since they overlap each other, we only see 6.)
what, a 7-gonal mirror would give 14 spikes to a bright star?

Yup. An even number of edges will produce the same number of spikes as edges. An odd number will produce twice the number as edges. You'll see it on some APODs taken with ordinary camera lenses. The most common lens irises are made with 9 leaves, and you'll see 18 spikes around bright light sources. See for instance this from last month: https://apod.nasa.gov/apod/ap230213.html

Posted: **Sun Mar 19, 2023 3:26 am**

AVAO wrote: ↑Sat Mar 18, 2023 5:54 pm
APOD Robot wrote: ↑Sat Mar 18, 2023 4:06 am Wolf-Rayet 124
I also like geck's version

biggg:https://live.staticflickr.com/65535/527 ... 8fae_o.png
Credit: NASA/ESA/CSA/ Judy Schmidt

Comment "This version of WR 124 is a combination of Hubble and JWST MIRI data. A press release recently featured the same data, and since this is one of my favorite objects, of course I had to have a go at it. The official release from the ERO team was a little bit dark. I also went ahead and used the same G'MIC processing to remove much of the banding noise from the dark parts of the image, allowing me to make it even brighter."

Red: JWST/MIRI F1800W
Yellow: JWST/MIRI F1280W
Yellow-Green: JWST/MIRI F1130W
Cyan: JWST/MIRI F770W
Blue: HST WF/PC2 F656N

I think got what visually flattened the cloud in APOD-posted NIRCAM+MIRI: of course, the 2-folded use of RGB to present NIRCAM's range and MIRI's range.
When you use a monotonic mapping, the cloud gets a 3d look ok.
And it looks 3d as well in MIRI range only (Blue: F090W + F150W + F770W, Green: F210M + F335M+ F1130W, Red: F444W + F470N + F1280W + F1800W):

And it looks 3d as well in the visual range:

Starship Asterisk*

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