Starship Asterisk*

by **MelvzLuster** » Sun Feb 19, 2023 4:18 pm

Great & wonderful scenario of ZTF Comet & Mars! A sign that we have a spectacular healthy space in a Universe full of wonders & mystery. Yes, we have an Infinite Cosmos ever expanding directly proportional to the increase in population growth of our planet Earth. Our eternal Universe approves and favors our worthwhile endeavor to explore & inhabit Mars & other habitable exoplanets. For these reasons, we are going to live forever conquering the infinity & vastness of the Universe for all eternity! And so it is!

by **Lorenzo Comolli** » Fri Feb 17, 2023 2:18 pm

I think that the APOD caption should include a sentence like:

This image is an artistic composition of images taken from the same location but at different sky positions, times and focal lengths respect to the final composition. This is not representing the real sky.

The actual sentence informing about the image tecniques is

Both the foreground and background images were taken on the same evening by the same camera and from the same location.

but I think it is misleading, implying that taking the images in this way is sufficient to give a realistic view.

Regards,
Lorenzo

by **jfgout** » Fri Feb 17, 2023 3:29 am

I note that the author is in no hurry to answer problematics questions such as: what focal length was used for the two different images. Before this thread gets completely forgotten, I'm going to write my own "honest" version of this APOD's description:

Reading back the description for this image, I'm amazed by this part: "The comet's white dust tail is visible to the right of the green coma, while the light blue ion tail trails towards the top of the image." Well, there is no white nor blue in this image of the comet, it is all green! It made me want to write a "honest" description of the picture (in the same spirit as honest trailers for movies...):

Donato went to the magnificent Swiss Alps to capture this beautiful conjunction of C/2022 with Mars. Shortly after sunset, he captured a wide-angle view of the the Matterhorn and surrounding mountains. He then used a telephoto lens with a much longer focal length to record images of the comet while it was almost directly overhead and recorded 60 frames of 2 minutes each while tracking the sky with an equatorial mount. Because the comet's motion relative to the background sky was consequent in 2 hours (~15' or half the size of the angular size of the full moon), the final composite requires mixing together a layer of stacked images tracked on the comet with another layer of stacked images tracked on the stars. Succumbing to the constant buzz about the GREEN comet, Donato could not resist and he moved the white balance cursors through the roof in the comet layer to make it appear as green as possible. Unfortunately, by doing so, he removed the subtle white/yellowish color of the dust tail and the delicate blue colors in the ion tail.
After merging the comet and background sky layers, the author decided that it would look great with the Matterhorn in the foreground and blended in the landscape picture taken earlier, positioning the sky in a way to produce the best possible looking composition.

For reasons that escape our comprehension, the author resisted the temptation to also include a view of the Eiffel tower in the foreground, but he insisted on the fact that both the sky and the landscape images had been taken during the same night, from the same camera, as if this was a token of authenticity.

Maybe I should offer my services to the APOD as a text writer

jf

PS: Just to be clear, I totally understand that the authors of the APOD do not have the time to investigate the many images submitted. That's also why I think it is important that the astrophotography community does this job of pointing out data manipulation problems that do not respect APOD's ethical statement.

by **Michael Teoh** » Wed Feb 15, 2023 9:02 pm

Lorenzo Comolli wrote: ↑Tue Feb 14, 2023 9:10 pm Dear Donato, great to have you here.
Please can you reply to questions posed by others? They whould greatly help to understand how the image was made, than anyone can judge if it is ok or not.

1. Focal lenght of the two images (and eventual crop factor). Can you share 2 originals uncropped?
2. Location (Gornergrat?) How was imaging at night in shuch high altitude in winter?
3. Date time of the two images
4. Did you shot a reference image at the date time of the composition? I.e. at comet mars setting. Can you share?
5. Which processing steps caused the dark nebula stand in front of the mars glare?

Ciao,
Lorenzo

I would add:

6. Did you mention it being a composite in your submission to APOD? You did in your FB/IG post, but in the submission?

I have seen the APOD authors mentioning an image being composite when it was, so I'm sure they won't miss it if you did mentioned.

As Tom suggested, a revised description would at least settle the part on misleading information. As for whether it was a badly done composite or not, that most likely will continue to be debated.

by **SpookyAstro** » Wed Feb 15, 2023 3:35 pm

rcolombari wrote: ↑Wed Feb 15, 2023 10:16 am Hi Tom!
What you call a simple correction in the APOD description has a deep meaning IMHO and deserves some further toughts.

As we pointed out the comet is at the right place for the date and time declared by the author but there's a whole amount of sky that doesn't show up to the West. At the time the comet has been imaged, ZTF and Mars were around 50º-60º up in the sky while in the image they look pretty low.
Moreover, as Lorenzo highlighted, the glare of Mars is behind the dark nebula. How could it be possible?

All these considerations lead to just a conclusion: copy and past of 2 different images resulting in something that never happened. The sky simply wasn't in this configuration.
How can such an image be APOD worthy?
It's true that, besides what many out there think, APOD doesn't mean that the images are chosen by NASA or pass through a peer review before getting published or must have a specific scientific meaning (NASA is just the hosting as far as I know, nothing less or more than this). Nevertheless, since the APOD audience is really wide, I think that the images should at least meet some basic astroimaging criteria.

Hi Roberto!! Hope all is well with you

Right I read about the orientation of the sky being incorrect based on what it would look like, I for sure agree with you and others that have stated this 100%. This image doesn't represent reality.

I guess my point is that it is very difficult to explain how this astroimage was assembled to match up with how it would look if you were there and were viewing it with a good pair of binoculars because it wouldn't look like this at all since the sky is not orientated correctly in this image. So what at this point I think is most important is to modify the description of the image at the very least to say that it's an 'artistic interpretation' or something like that as it doesn't qualify under the commonly understood definition of a composite astroimage since the sky is registered using a different coordinate system as the author stated in an earlier comment. I'm going to tread lightly here but I would kind of consider this as something like the artistic renderings of what it would look like if you were on an exoplanet looking at the night sky, it's not really based on reality it's an artistic expression type deal. Like this APOD and others like it: https://apod.nasa.gov/apod/ap050805.html

I'm not sure what qualifies any image to be published as APOD, I'll leave that up to the editors and I think that their freedom/flexibility to publish a varying array of different types of images/renderings/art etc is what makes APOD great in my opinion. Are their better more accurate examples of what this event looked like in our night sky, I would say yes. Should any of those images replace this one? That's totally up to the editors.

Clear skies bud!

Tom

by **johnnydeep** » Wed Feb 15, 2023 3:09 pm

Chris Peterson wrote: ↑Tue Feb 14, 2023 9:09 pm
johnnydeep wrote: ↑Tue Feb 14, 2023 4:02 pm
Chris Peterson wrote: ↑Tue Feb 14, 2023 12:21 am

The 18 spikes on Mars are what you get with a nine-bladed iris on the camera lens, which is a very common number. Instead of a circular aperture you have a polygon with 9 sides (a nonagon). Each straight edge creates a pair of diffraction spikes. So you end up with 18.

Ion tails are often quite straight because they are driven by high speed solar wind and point directly away from the Sun. Dust tails are often much more diffuse because they diffuse evenly away from the comet and then their particles move at different speeds depending on whether they are inside or outside the parent body orbit. And they interact with solar radiation, not the solar wind, which results in a much more scattered direction for these large particles (as opposed to the gas molecules or atoms that make up the ion tail).
Thanks. I get the nonagon aperture explanation. As for dust -vs- ions/atoms being acted upon by radiation -vs- solar wind, does the radiation not affect ions/atoms simply because they are much smaller than (the vast majority) of the wavelengths hitting them? And why doesn't the solar wind exert a force on the dust? Or is it just that the force is tiny relative to the dust grains? [ Bonus question: what's the force of solar radiation compared to that of the solar wind on an aluminum foil square foot at the distance of Earth's orbit? (I assume the material making up that square foot matters a great deal as well?) ]
The solar wind consists of charged particles, which interact electromagnetically with the ion tail. Photon pressure is exerted when photons are reflected by a surface (or absorbed and re-emitted), with a partial transfer of momentum. A macroscopic particle is more likely to interact with a photon (or photons) than a small molecule. And the forces generated by the electromagnetic interaction are much larger. So the solar wind dominates the ion tail. As the dust tail is largely neutral, its interaction with the solar wind is much smaller.

Ah, yes, I completely forgot about the charged particles! Makes sense now - thanks!

by **rcolombari** » Wed Feb 15, 2023 10:16 am

Hi Tom!
What you call a simple correction in the APOD description has a deep meaning IMHO and deserves some further toughts.

As we pointed out the comet is at the right place for the date and time declared by the author but there's a whole amount of sky that doesn't show up to the West. At the time the comet has been imaged, ZTF and Mars were around 50º-60º up in the sky while in the image they look pretty low.
Moreover, as Lorenzo highlighted, the glare of Mars is behind the dark nebula. How could it be possible?

All these considerations lead to just a conclusion: copy and past of 2 different images resulting in something that never happened. The sky simply wasn't in this configuration.
How can such an image be APOD worthy?
It's true that, besides what many out there think, APOD doesn't mean that the images are chosen by NASA or pass through a peer review before getting published or must have a specific scientific meaning (NASA is just the hosting as far as I know, nothing less or more than this). Nevertheless, since the APOD audience is really wide, I think that the images should at least meet some basic astroimaging criteria.

by **SpookyAstro** » Wed Feb 15, 2023 6:30 am

I've had to give a run down of this image to a few laypeople lately who have asked about it and it has been been pretty difficult.

I won't belabor the point of the technical issues which have already been laid out quite well in this thread and elsewhere on web. But I think it's important to make a correction at this point in the description of the image relating to the 'Both the foreground and background images were taken on the same evening by the same camera and from the same location.' part. I've found it more easy to say that it's an artistic rendering/representation, similar to how APODs in the past have done so for things that don't completely match up with 'reality' or how it would look exactly but may still have value.

I would like to also add that I don't fault the editors who have done such a great job overall considering the task of running APOD and sometimes things go this way, at this point it appears to be just a matter of a simple correction in the description and then call it done IMHO.

Tom Masterson
www.transientastronomer.com

by **Lorenzo Comolli** » Tue Feb 14, 2023 9:10 pm

Dear Donato, great to have you here.
Please can you reply to questions posed by others? They whould greatly help to understand how the image was made, than anyone can judge if it is ok or not.

1. Focal lenght of the two images (and eventual crop factor). Can you share 2 originals uncropped?
2. Location (Gornergrat?) How was imaging at night in shuch high altitude in winter?
3. Date time of the two images
4. Did you shot a reference image at the date time of the composition? I.e. at comet mars setting. Can you share?
5. Which processing steps caused the dark nebula stand in front of the mars glare?

Ciao,
Lorenzo

by **Chris Peterson** » Tue Feb 14, 2023 9:09 pm

johnnydeep wrote: ↑Tue Feb 14, 2023 4:02 pm
Chris Peterson wrote: ↑Tue Feb 14, 2023 12:21 am
johnnydeep wrote: ↑Mon Feb 13, 2023 8:55 pm So why are there 18 (I think) diffraction spikes on Mars? And why is the ion tail so thin and arrow-straight compared to the broad and curved dust trail? I guess this is a question about comet tails in general now that I think about it. Both tails are made of matter (ions/dust) in orbit while also being pushed by sunlight, so why don't they look roughly similar?
The 18 spikes on Mars are what you get with a nine-bladed iris on the camera lens, which is a very common number. Instead of a circular aperture you have a polygon with 9 sides (a nonagon). Each straight edge creates a pair of diffraction spikes. So you end up with 18.

Ion tails are often quite straight because they are driven by high speed solar wind and point directly away from the Sun. Dust tails are often much more diffuse because they diffuse evenly away from the comet and then their particles move at different speeds depending on whether they are inside or outside the parent body orbit. And they interact with solar radiation, not the solar wind, which results in a much more scattered direction for these large particles (as opposed to the gas molecules or atoms that make up the ion tail).
Thanks. I get the nonagon aperture explanation. As for dust -vs- ions/atoms being acted upon by radiation -vs- solar wind, does the radiation not affect ions/atoms simply because they are much smaller than (the vast majority) of the wavelengths hitting them? And why doesn't the solar wind exert a force on the dust? Or is it just that the force is tiny relative to the dust grains? [ Bonus question: what's the force of solar radiation compared to that of the solar wind on an aluminum foil square foot at the distance of Earth's orbit? (I assume the material making up that square foot matters a great deal as well?) ]

The solar wind consists of charged particles, which interact electromagnetically with the ion tail. Photon pressure is exerted when photons are reflected by a surface (or absorbed and re-emitted), with a partial transfer of momentum. A macroscopic particle is more likely to interact with a photon (or photons) than a small molecule. And the forces generated by the electromagnetic interaction are much larger. So the solar wind dominates the ion tail. As the dust tail is largely neutral, its interaction with the solar wind is much smaller.

by **stephenramsden** » Tue Feb 14, 2023 8:54 pm

I just can’t believe they didn’t throw in an ISS transit. Afterall, it’s an APOD, right?

by **johnnydeep** » Tue Feb 14, 2023 4:02 pm

Chris Peterson wrote: ↑Tue Feb 14, 2023 12:21 am
johnnydeep wrote: ↑Mon Feb 13, 2023 8:55 pm So why are there 18 (I think) diffraction spikes on Mars? And why is the ion tail so thin and arrow-straight compared to the broad and curved dust trail? I guess this is a question about comet tails in general now that I think about it. Both tails are made of matter (ions/dust) in orbit while also being pushed by sunlight, so why don't they look roughly similar?
The 18 spikes on Mars are what you get with a nine-bladed iris on the camera lens, which is a very common number. Instead of a circular aperture you have a polygon with 9 sides (a nonagon). Each straight edge creates a pair of diffraction spikes. So you end up with 18.

Ion tails are often quite straight because they are driven by high speed solar wind and point directly away from the Sun. Dust tails are often much more diffuse because they diffuse evenly away from the comet and then their particles move at different speeds depending on whether they are inside or outside the parent body orbit. And they interact with solar radiation, not the solar wind, which results in a much more scattered direction for these large particles (as opposed to the gas molecules or atoms that make up the ion tail).

Thanks. I get the nonagon aperture explanation. As for dust -vs- ions/atoms being acted upon by radiation -vs- solar wind, does the radiation not affect ions/atoms simply because they are much smaller than (the vast majority) of the wavelengths hitting them? And why doesn't the solar wind exert a force on the dust? Or is it just that the force is tiny relative to the dust grains? [ Bonus question: what's the force of solar radiation compared to that of the solar wind on an aluminum foil square foot at the distance of Earth's orbit? (I assume the material making up that square foot matters a great deal as well?) ]

by **jfgout** » Tue Feb 14, 2023 3:43 pm

Roberto Colombari wrote: ↑Tue Feb 14, 2023 2:37 pm There remain few points that are really a little bit confusing at least for me.
You shot the Comet-Mars conjunction from sunset 'till 22:45, local time approximately.
At this time there's still a good amount of sky (Jupiter, Cetus, etc...) between them and the horizon where they'll set later one. Why can't we see them in the image?

Cheers

Roberto,

The author was fairly clear in their answer on this point:

What I did was to take the foreground exposure after sunset during the blue hour pointing the camera north west where, as planned with Stellarium, the comet would set early in the morning of the 11. Then, from the exact same tripod position, I tilted the camera up and framed the comet with mars (and part of the dark nebula). I then took a series of exposures until 30 minutes more or less after moonrise…
[...]
Then I combined blended the sky with the foreground.

The implicit part is that combining the sky with the foreground should represent the sky as it was when the comet/Mars were setting behind the mountains (= a few hours after the background sky images were taken). I wont blame the author for not spending the night at the Gornergrat, it is cold up there!!!

. The problem is that the result is far from what the sky would have looked like (sure, it could have been worse if the picture had been taken from the North side of the Matterhorn for example...).

Again, when you read the answer from the author, they do stress that the pictures were taken "from the exact same tripod position". What is the point of stressing this, if not to make people believe that this composite represents something real? Based on all the issues that have been pointed out, why bother using a foreground image taken on the same night, or even from the same place?

Cheers,

jf

by **Roberto Colombari** » Tue Feb 14, 2023 2:37 pm

There remain few points that are really a little bit confusing at least for me.
You shot the Comet-Mars conjunction from sunset 'till 22:45, local time approximately.
At this time there's still a good amount of sky (Jupiter, Cetus, etc...) between them and the horizon where they'll set later one. Why can't we see them in the image?

Cheers

by **jfgout** » Tue Feb 14, 2023 2:27 pm

Donato wrote: ↑Tue Feb 14, 2023 8:05 am Dear @Jfgout and @Ann,

Thanks for your review even though frankly I believe you are a bit too strong in your words and frankly, especially from professionals or anyway experts, I would expect a bit less aggressive/offensive tones and more constructive words… anyway let me please try again

I clearly mentioned that this is a composite image. Please check yourself my IG page… so the whole presumed root cause of hiding things etc is a bit difficult to understand for me as from the very beginning I have not hidden it is indeed a composite image.
Please check yourself in stellarium (I hope to find a way to paste a screenshot) and you will see that the sky is aligned using celestial/equatorial coordinates. I could have used azimuthal coordinates but I preferred to use celestial ones when taking the sky… shall I be killed for this ? Not sure frankly
Indeed I augmented the saturation in post processing as already explained: it is my personal opinion (and as such I might be totally wrong) that in 100% of astro photography pictures the saturation is increased in post…maybe I could have done it better but, once again, shall I be killed for this ? Not sure

Bottom line is at least for me: as a non professional who is indeed prone to errors (even though I giorni was able to explain myself and how I imaged the picture), I would have expected a significant more constructive criticisms and not attacks like I have read… or at least this is what I do in my profession/hobbies when I see some opportunity for improvements

Dear Donato,

I'm sorry if you've found my words too strong or my tone aggressive, but all I did was demonstrate, using math and basic astronomy/photography knowledge all the manipulations in your image which I think should have been made clear from the start. In my book, that's constructive criticism. But sure, you can reply with things like "shall I be killed for this?" while ignoring all the important details (was the picture taken from the Gornergrat?, which focal lengths were used?) to pretend that you are a victim of extremists like me...

So, yes, you did mention from the start that this was a composite image (I mean, no one in their wright mind would try to pass this as a one shot) but failed to mention any of the many issues that I have mentioned. Then, why go through the trouble of specifying that the different parts of the composite were taken on the same day with the same camera? If you change the lens, paste the sky background in an impossible position relative to the foreground and at a 45 degrees angle after saturating the greens to the max (I mean, the white stars leave a green trail on your picture!!!!), why not go all the way and also add the Eiffel tower or the leaning tower of Pisa in the image?

Please check yourself in stellarium (I hope to find a way to paste a screenshot) and you will see that the sky is aligned using celestial/equatorial coordinates. I could have used azimuthal coordinates but I preferred to use celestial ones when taking the sky…

This does not mean anything. An alignment is relative to something. In your case, it seems logical to use the foreground (the mountains) as the baseline. Again, if you do this, why stop there and not use an image taken at a different time and from a different place for your foreground?

After you mentioned it, I searched for your previous APOD. Well, it's a very nice image (congratulations). It might would have been nicer with a mountain in the foreground

Roberto Colombari wrote: ↑Tue Feb 14, 2023 12:53 pm From Gornergrat you spot Monte Cervino a few degrees South when looking to straight to West; let it be, as you said, azimuth between 260º and 265º.
Now, reading what they guy wrote ("I shot Mars and the Comet till the Moon rise" [i.e., ~22:45 local time]), it's not so unlikely to have Mars on that side of Monte Cervino.

Of course, at the time he took the background sky pictures, Mars was close to the meridian (azimuth ~180 degrees). But at that time, it was also 60 degrees above the horizon!!! So, a picture with the Matterhorn in it taken at this time would have a LOT of sky between the mountain (horizon) and Mars/Comet (constellations of Pisces and Cetus, Jupiter would be visible, ...). If you paste the sky in the location where it would have been at the time the comet/Mars were approaching the west horizon, try to do it reasonably correctly.

Now, there are lots of good things: there is plenty of signal, the dark nebula is nice. So, I'll end my message on this positive note.

jf

by **donato** » Tue Feb 14, 2023 1:20 pm

Thanks Roberto for the feedback...so I hope the topic is now closed and I can relax...it was actually a bit frustrating (and stressful) for me because I felt attacked (too much frankly speaking)...and I was not expecting that, especially considering that nothing at all like this happened for my other apod. Now I know what can be expected

Ciao,
Donato

by **Roberto Colombari** » Tue Feb 14, 2023 1:04 pm

Yeah, that's right. At that time the Comet had a declination far northern than Mars. I read 11th of February meant as the night of the 11th of February

by **donato** » Tue Feb 14, 2023 1:00 pm

Roberto Colombari wrote: ↑Tue Feb 14, 2023 12:37 pm > can you please tell me how can I attach an image when posting a reply so that i can attach my screen shot

You have to upload the screenshot on postimage.org, for instance, get the direct link to the image and put it here.

> you rotated the celestial coordinates by ~180-45=135 degrees instead of rotating by 45 degrees

I've simply aligned the sky of your picture with Stellarium. If you look at it both the screenshots have the same position angle, more or less.
The point that I have probably missed is that you shot the comet the night between 10 and 11 of February, right? When it really had further north declinations than Mars. I thought you shot it the next night when it got southern.

Dear @Roberto Colombari,

You can find the screenshot here: https://i.postimg.cc/yWqkfDRt/screenshot-stellarium.jpg
And thanks for the tip on how to add an image in the thred.
You will see in the screenshot that the position of mars and comet is indeed correct. The photos were taken during the nught between the 10th and 11th of Feb, as written in some other replies. The screenshot I linked is according to this.

I hope I clarified...

by **Roberto Colombari** » Tue Feb 14, 2023 12:53 pm

jfgout wrote: ↑Tue Feb 14, 2023 2:40 am
2) I have strong doubts about the location the sky relative to the mountain. This one is tricky to check without knowing the exact location of where the picture was taken. I'm going to assume that it was taken from the Gornergrat observatory area. This would put the summit of Matterhorn at a 265 degrees heading. When Mars was ~5 degrees above the horizon on that day, its azimuth was 300 degrees. So (assuming that I did not mess up too much my guess about the location from where the photo was taken), not only is the orientation of the sky not correct, it is also not placed correctly relative to the foreground. Mars should be on the other side of the Matterhorn.

jf

From Gornergrat you spot Monte Cervino a few degrees South when looking to straight to West; let it be, as you said, azimuth between 260º and 265º.
Now, reading what they guy wrote ("I shot Mars and the Comet till the Moon rise" [i.e., ~22:45 local time]), it's not so unlikely to have Mars on that side of Monte Cervino.

Cheers

by **Roberto Colombari** » Tue Feb 14, 2023 12:37 pm

> can you please tell me how can I attach an image when posting a reply so that i can attach my screen shot

You have to upload the screenshot on postimage.org, for instance, get the direct link to the image and put it here.

> you rotated the celestial coordinates by ~180-45=135 degrees instead of rotating by 45 degrees

I've simply aligned the sky of your picture with Stellarium. If you look at it both the screenshots have the same position angle, more or less.
The point that I have probably missed is that you shot the comet the night between 10 and 11 of February, right? When it really had further north declinations than Mars. I thought you shot it the next night when it got southern.

by **donato** » Tue Feb 14, 2023 12:29 pm

Dear @Roberto Colombari,

can you please tell me how can I attach an image when posting a reply so that i can attach my screen shot? you rotated the celestial coordinates by ~180-45=135 degrees instead of rotating by 45 degrees...so what you write I am sorry but I think it is misleading... please tell me how can I add my screenshot to the thread make copy and paste but it is not working...shall I register or something? It is a bit unfair if I cannot show you exactly what I mean frankly speaking

by **Roberto Colombari** » Tue Feb 14, 2023 12:18 pm

Now the question is how the comet ended up with a further north declination compared to Mars while it's exactly the opposite.
I really would remove this image from APOD. I am not talking about the quality of the processing, anyone has his/her own style.
In this case this image is simply wrong.

by **Donato** » Tue Feb 14, 2023 8:05 am

Dear @Jfgout and @Ann,

Thanks for your review even though frankly I believe you are a bit too strong in your words and frankly, especially from professionals or anyway experts, I would expect a bit less aggressive/offensive tones and more constructive words… anyway let me please try again

I clearly mentioned that this is a composite image. Please check yourself my IG page… so the whole presumed root cause of hiding things etc is a bit difficult to understand for me as from the very beginning I have not hidden it is indeed a composite image.
Please check yourself in stellarium (I hope to find a way to paste a screenshot) and you will see that the sky is aligned using celestial/equatorial coordinates. I could have used azimuthal coordinates but I preferred to use celestial ones when taking the sky… shall I be killed for this ? Not sure frankly
Indeed I augmented the saturation in post processing as already explained: it is my personal opinion (and as such I might be totally wrong) that in 100% of astro photography pictures the saturation is increased in post…maybe I could have done it better but, once again, shall I be killed for this ? Not sure

Bottom line is at least for me: as a non professional who is indeed prone to errors (even though I giorni was able to explain myself and how I imaged the picture), I would have expected a significant more constructive criticisms and not attacks like I have read… or at least this is what I do in my profession/hobbies when I see some opportunity for improvements

by **Ann** » Tue Feb 14, 2023 5:38 am

There is a great photo of Comet ZTF, Mars and Barnard 22 (and the Pleiades) by Luca Fornaciari in the Recent Submissions thread.

Do look at the full size image.

Ann

by **jfgout** » Tue Feb 14, 2023 2:40 am

Ann wrote: ↑Mon Feb 13, 2023 7:25 am
Well, what do you think? It's the same dark nebula, isn't it?

And isn't it interesting that the photographer has managed to bring out this nebula? It sure isn't often that we see dark nebulas showing up in images that are meant to show us something else entirely. I'm not talking about iconic dark nebulas like the Coalsack Nebula or the Pipe Nebula, but anonymous and unfamiliar dark nebulas like Barnard 22.

This certainly says something about how the photographer created his image. But I'll leave that to the many photo experts (Chris?) at Starship Asterisk* to explain.

Ann

While I 100% share your concern about the (excess of) green, this patch of dark nebula is not so difficult to catch in pictures. This being said, there are so many problems with this image (most have already been pointed out, but I'll take a turn at beating the dead horse... and clarifying a few things). I appreciate the author coming here and discussing this, although I note that they did not provide any of the information that could help (or incriminate...) such as: the exact location from where this picture was taken and the focal length of the lens used. Instead, we are served the usual feel good story ("I drove 6 hours to go get this picture, totally worth it!" and the now common but HUGE red flag: "Images taken during the same night, from the same place and with the same camera").

Okay, so here is my list of everything wrong with this picture, in no particular order.

1) The orientation of the sky relative to the horizon is wrong. On this picture, tau Tau (that's funny...), 95 tau, Mars, and the top part of IC2087 (the dark nebula) form more or less a horizontal line. Another way to say that is that the line joining tau tau to Mars is ~parallel to the horizon. But from this part of the world, shortly before setting, this line should form an ~45 degrees angle with the horizon. Anyone can use STellarium (or other) to check this.
In other words: the sky orientation is rotated ~45 degrees relative to reality.

2) I have strong doubts about the location the sky relative to the mountain. This one is tricky to check without knowing the exact location of where the picture was taken. I'm going to assume that it was taken from the Gornergrat observatory area. This would put the summit of Matterhorn at a 265 degrees heading. When Mars was ~5 degrees above the horizon on that day, its azimuth was 300 degrees. So (assuming that I did not mess up too much my guess about the location from where the photo was taken), not only is the orientation of the sky not correct, it is also not placed correctly relative to the foreground. Mars should be on the other side of the Matterhorn.

3) Sky and foreground were most likely taken with different sampling sizes (= different scale). A quick plate solving of the image indicates an image scape of 7.09"/pixel (on 4229x3838 full resolution image). On that same image, the height of the edge above Hörnlihütte (the shoulder on the right side of the mountain) is 591 pixels. These 591 pixels represent 1200 meters (the difference in elevation between Hörnlihütte and the summit) or 4190 arcseconds (591*7.09), using the previously obtained sampling scale. For 1200 meters to cover 4190 arcseconds, one would need to be standing ~50 km away from the Matterhorn. That is ~5x the distance from the Gornergrat. So, unless there is a secret spot to take this picture of the Matterhorn from 50 km away (unlikely), or the foreground (mountain) is simply 5 times smaller than what it should be if it had been take with the same sampling size (=same camera and same focal length) as the background sky.

4) As previously mentioned, the comet is waaaayyyyy too green. We can see that the leftover trails made by the brightest stars (trails from staking/tracking on the comet, which moves fast relative to the background stars) are all green. This clearly tells us that the author turned the color balance/saturation to the top in the green for the layer that contains the image tracked/stacked on the comet.

5) At the time Mars and the comet were that low in the sky, the foreground would have been inundated by the light from the gibbous Moon.

6) Absolutely zero trace of atmospheric extinction. Even in the transparent skies of high elevation Gornergrat, there should be some level of atmospheric extinction visible. On this part, the author was honest in their follow up, explaining that the background sky was captured shortly after nightfall (and before moonrise), when the Mars/Comet duo was high in the sky (and nowhere near the horizon).

So, to summarize, this image shows a comet with an absurdly green color, in the wrong location relative to the foreground, with a sky at a 45 degrees angle from reality and with a factor 5 difference in the scale between the foreground and the sky. As someone suggested, at this point, why not just use a picture of the Eiffel tower in the foreground? Or a macro shot of a beautiful mountain flower (okay, not many flowers in February in the Alps...)

What really bothers me is the use of the this: "Both the foreground and background images were taken on the same evening by the same camera and from the same location." This sentence is clearly there to let us believe that this picture represents some sort of reality. For all the reasons that I have detailed above, it is clearly NOT the case.

APOD has an ethic statement which reads: "APOD accepts composited or digitally manipulated images, but requires them to be identified as such and to have the techniques used described in a straightforward, honest and complete way." In my view, the description for this image should include the fact that different focal lengths were used for the sky and the foreground, the fact that the sky was positioned on the left of the mountain and rotated 45 degrees because it looked nicer and that the colors of the comet had been boosted in the green through the roof.

I know that the authors of the APOD do this on their free time and I certainly appreciate their work. It might be nice to have a group of "reviewers" (experienced astrophotographers) who could share their opnion with the APOD's editors and share their concerns before a photo with extensive digital manipulation is published. The APOD used to be some sort of holly grail for amateur astronomers, but more and more people in the hobby are having a negative view of it because of these images that can be considered "fake". I still love the APOD, but I would love to see a better/strict implementation of the ethics statement mention earlier.

jf

Starship Asterisk*

APOD: Comet ZTF and Mars (2023 Feb 13)

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