Starship Asterisk*

by **alter-ego** » Sun Nov 15, 2020 5:15 am

Chris Peterson wrote: ↑Sun Nov 15, 2020 5:06 am
alter-ego wrote: ↑Sun Nov 15, 2020 4:54 am
johnnydeep wrote: ↑Sat Nov 14, 2020 10:21 pm
Neat!
There's more than enough visible detail to determine the field by eye when overlapping images. Having an FOV [X,Y] error of [10",6"], the visually dialed-in DSS2 image with the APOD image is shown in the hover-image below. I normally don't attempt that level of precision, but I was curious how well I could measure the FOV given Ignacio's stated dimensions.
We should note, however, that a proper plate solution goes well beyond providing the FOV. It identifies the center of the plate to a fraction of a pixel, as well as a set of mathematical coefficients that describe rotation and a number of different mapping distortions. Using the values generated by the plate solution, the astrometric position (RA and declination) of any star or structure in the image can be calculated with sub-pixel accuracy.

Yeah, no doubt is a powerful tool. Although I've not needed that analysis power myself, I have to admit it occasionally might save me some time.

by **Chris Peterson** » Sun Nov 15, 2020 5:06 am

alter-ego wrote: ↑Sun Nov 15, 2020 4:54 am
johnnydeep wrote: ↑Sat Nov 14, 2020 10:21 pm
Chris Peterson wrote: ↑Sat Nov 14, 2020 7:51 pm

It can be done inside some image processing programs (this image was processed with PixInsight, which has a plate solving tool). It can also be done by uploading an image to Astrometry.net, which can solve almost anything. This image has almost all the stars processed out, by virtue of so much signal coming from a very narrow H-alpha and OIII channels. But there were probably enough stars in the unprocessed frames to get a solution. It's also easy enough to just solve a clean star field, which will give you the pixel scale for a given imaging train, and just use that value, multiplied by the number of pixels on an axis.
Neat!
There's more than enough visible detail to determine the field by eye when overlapping images. Having an FOV [X,Y] error of [10",6"], the visually dialed-in DSS2 image with the APOD image is shown in the hover-image below. I normally don't attempt that level of precision, but I was curious how well I could measure the FOV given Ignacio's stated dimensions.

We should note, however, that a proper plate solution goes well beyond providing the FOV. It identifies the center of the plate to a fraction of a pixel, as well as a set of mathematical coefficients that describe rotation and a number of different mapping distortions. Using the values generated by the plate solution, the astrometric position (RA and declination) of any star or structure in the image can be calculated with sub-pixel accuracy.

by **alter-ego** » Sun Nov 15, 2020 4:54 am

johnnydeep wrote: ↑Sat Nov 14, 2020 10:21 pm
Chris Peterson wrote: ↑Sat Nov 14, 2020 7:51 pm
johnnydeep wrote: ↑Sat Nov 14, 2020 7:30 pm

Ok. I had to look up "plate-solving". Did you do this with software or manually? And, again, assuming your FOV is correct, the APOD is wrong to say it is 2 degrees wide, right?
It can be done inside some image processing programs (this image was processed with PixInsight, which has a plate solving tool). It can also be done by uploading an image to Astrometry.net, which can solve almost anything. This image has almost all the stars processed out, by virtue of so much signal coming from a very narrow H-alpha and OIII channels. But there were probably enough stars in the unprocessed frames to get a solution. It's also easy enough to just solve a clean star field, which will give you the pixel scale for a given imaging train, and just use that value, multiplied by the number of pixels on an axis.
Neat!

There's more than enough visible detail to determine the field by eye when overlapping images. Having an FOV [X,Y] error of [10",6"], the visually dialed-in DSS2 image with the APOD image is shown in the hover-image below. I normally don't attempt that level of precision, but I was curious how well I could measure the FOV given Ignacio's stated dimensions.

: Click to view full size image 1 or image 2

by **johnnydeep** » Sat Nov 14, 2020 10:21 pm

Chris Peterson wrote: ↑Sat Nov 14, 2020 7:51 pm
johnnydeep wrote: ↑Sat Nov 14, 2020 7:30 pm
ignacio_db wrote: ↑Fri Nov 13, 2020 7:58 pm

By plate-solving the image.

Ignacio
Ok. I had to look up "plate-solving". Did you do this with software or manually? And, again, assuming your FOV is correct, the APOD is wrong to say it is 2 degrees wide, right?
It can be done inside some image processing programs (this image was processed with PixInsight, which has a plate solving tool). It can also be done by uploading an image to Astrometry.net, which can solve almost anything. This image has almost all the stars processed out, by virtue of so much signal coming from a very narrow H-alpha and OIII channels. But there were probably enough stars in the unprocessed frames to get a solution. It's also easy enough to just solve a clean star field, which will give you the pixel scale for a given imaging train, and just use that value, multiplied by the number of pixels on an axis.

Neat!

by **Chris Peterson** » Sat Nov 14, 2020 7:51 pm

johnnydeep wrote: ↑Sat Nov 14, 2020 7:30 pm
ignacio_db wrote: ↑Fri Nov 13, 2020 7:58 pm
johnnydeep wrote: ↑Fri Nov 13, 2020 7:38 pm

So, this is roughly 1 degree x 1 degree, and not 2 degrees wide per the text? How did you determine the exact field of view?
By plate-solving the image.

Ignacio
Ok. I had to look up "plate-solving". Did you do this with software or manually? And, again, assuming your FOV is correct, the APOD is wrong to say it is 2 degrees wide, right?

It can be done inside some image processing programs (this image was processed with PixInsight, which has a plate solving tool). It can also be done by uploading an image to Astrometry.net, which can solve almost anything. This image has almost all the stars processed out, by virtue of so much signal coming from a very narrow H-alpha and OIII channels. But there were probably enough stars in the unprocessed frames to get a solution. It's also easy enough to just solve a clean star field, which will give you the pixel scale for a given imaging train, and just use that value, multiplied by the number of pixels on an axis.

by **johnnydeep** » Sat Nov 14, 2020 7:30 pm

ignacio_db wrote: ↑Fri Nov 13, 2020 7:58 pm
johnnydeep wrote: ↑Fri Nov 13, 2020 7:38 pm
ignacio_db wrote: ↑Fri Nov 13, 2020 5:40 pm

The precise FOV is 1d 3' 47.8" x 1d 18' 46.0".

Ignacio
So, this is roughly 1 degree x 1 degree, and not 2 degrees wide per the text? How did you determine the exact field of view?
By plate-solving the image.

Ignacio

Ok. I had to look up "plate-solving". Did you do this with software or manually? And, again, assuming your FOV is correct, the APOD is wrong to say it is 2 degrees wide, right?

From https://www.astrophotography.app/usersg ... olving.htm

Plate-solving is a image analysis that detects the stars and then tries to identify them using catalogs of know stars. If the analysis is successful it is possible to calculate the Right Accession (RA) and Declination (Dec) of the image center which tells where exactly is pointing the telescope, image orientation, resolution and etc. Plate-solving is the engine of many scientific studies for example comet, asteroid hunting and orbit analysis.

Nowadays we are lucky to have access to many advanced techniques and devices that in the past were available only for the biggest professional observatories. Plate-solving is one these techniques that makes imaging much productive, accurate and pleasant. There are two types of solving - Near and Blind. The first one needs to know approximately where "you are" and solving will tell you exactly where "you are", it is very fast because you already know context . For the second one you don't need know where "you are" and solving will find the position without knowing the starting position, it is slower because there is need to match star patterns from all over the sky.

by **Chris Peterson** » Sat Nov 14, 2020 2:13 pm

Ann wrote: ↑Sat Nov 14, 2020 1:55 pm
Chris Peterson wrote: ↑Sat Nov 14, 2020 1:13 pm
Ann wrote: ↑Sat Nov 14, 2020 4:51 am

Okay, but this part of the Tarantula Nebula would surely be ablaze at a distance of only 1500 light-years, right?
You'd see a cluster of bright stars. The nebulosity wouldn't be anything other than a faint glow. If fact, the bright stars might make it harder to see than in some other parts.
I get it, Chris, but you know me... I often prefer the bright (blue) stars over the nebulosity anyway.

Surely R136 would look like a mighty impressive cluster from a distance of 1,500 light-years?

Ann

I'm not sure it would- it's pretty tiny. A lot of bright stars that are very close together might or might not look all that impressive to the naked eye. From 1500 ly, it would be about the same size as the Pleiades. Its dozen or so most luminous members would be about 1000 times brighter than the stars that make up the Pleiades... which sounds like a lot, but given the logarithmic nature of our vision, really isn't (7-8 magnitudes). I guess it would look like a fairly bright globular cluster- an obvious fuzzy spot in which those with good vision would see a few distinct stars, not unlike the Pleiades, but certainly brighter.

by **Ann** » Sat Nov 14, 2020 1:55 pm

Chris Peterson wrote: ↑Sat Nov 14, 2020 1:13 pm
Ann wrote: ↑Sat Nov 14, 2020 4:51 am
Chris Peterson wrote: ↑Fri Nov 13, 2020 11:32 pm

The problem is that even with 100% efficient eyes, you'd still need to stare at one spot in the sky for many minutes, and somehow integrate the photons your eyes were collecting, to see anything remotely like this.

In reality, if we were close enough to this to see it covering half the sky, it would look like a barely discernible gray haze, dimmer than the Milky Way.
Okay, but this part of the Tarantula Nebula would surely be ablaze at a distance of only 1500 light-years, right?
You'd see a cluster of bright stars. The nebulosity wouldn't be anything other than a faint glow. If fact, the bright stars might make it harder to see than in some other parts.

I get it, Chris, but you know me... I often prefer the bright (blue) stars over the nebulosity anyway.

Surely R136 would look like a mighty impressive cluster from a distance of 1,500 light-years?

Ann

by **Chris Peterson** » Sat Nov 14, 2020 1:13 pm

Ann wrote: ↑Sat Nov 14, 2020 4:51 am
Chris Peterson wrote: ↑Fri Nov 13, 2020 11:32 pm
Tarantulas are very nice wrote: ↑Fri Nov 13, 2020 10:31 pm

Imagine getting out of the cabin at night and seeing that across half the sky. Our view of nature would perhaps be rather less arrogant, and astronomy would be taken seriously indeed.

(We'd have H-alpha eyes, the right atmosphere, and a high tolerance for being blasted by supernovae, OK?)
The problem is that even with 100% efficient eyes, you'd still need to stare at one spot in the sky for many minutes, and somehow integrate the photons your eyes were collecting, to see anything remotely like this.

In reality, if we were close enough to this to see it covering half the sky, it would look like a barely discernible gray haze, dimmer than the Milky Way.
Okay, but this part of the Tarantula Nebula would surely be ablaze at a distance of only 1500 light-years, right?

You'd see a cluster of bright stars. The nebulosity wouldn't be anything other than a faint glow. If fact, the bright stars might make it harder to see than in some other parts.

by **Ann** » Sat Nov 14, 2020 4:51 am

Chris Peterson wrote: ↑Fri Nov 13, 2020 11:32 pm
Tarantulas are very nice wrote: ↑Fri Nov 13, 2020 10:31 pm
were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky
Imagine getting out of the cabin at night and seeing that across half the sky. Our view of nature would perhaps be rather less arrogant, and astronomy would be taken seriously indeed.

(We'd have H-alpha eyes, the right atmosphere, and a high tolerance for being blasted by supernovae, OK?)
The problem is that even with 100% efficient eyes, you'd still need to stare at one spot in the sky for many minutes, and somehow integrate the photons your eyes were collecting, to see anything remotely like this.

In reality, if we were close enough to this to see it covering half the sky, it would look like a barely discernible gray haze, dimmer than the Milky Way.

Okay, but this part of the Tarantula Nebula would surely be ablaze at a distance of only 1500 light-years, right?

Ann

by **Chris Peterson** » Fri Nov 13, 2020 11:32 pm

Tarantulas are very nice wrote: ↑Fri Nov 13, 2020 10:31 pm
were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky
Imagine getting out of the cabin at night and seeing that across half the sky. Our view of nature would perhaps be rather less arrogant, and astronomy would be taken seriously indeed.

(We'd have H-alpha eyes, the right atmosphere, and a high tolerance for being blasted by supernovae, OK?)

The problem is that even with 100% efficient eyes, you'd still need to stare at one spot in the sky for many minutes, and somehow integrate the photons your eyes were collecting, to see anything remotely like this.

In reality, if we were close enough to this to see it covering half the sky, it would look like a barely discernible gray haze, dimmer than the Milky Way.

by **Tarantulas are very nice** » Fri Nov 13, 2020 10:31 pm

were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky

Imagine getting out of the cabin at night and seeing that across half the sky. Our view of nature would perhaps be rather less arrogant, and astronomy would be taken seriously indeed.

(We'd have H-alpha eyes, the right atmosphere, and a high tolerance for being blasted by supernovae, OK?)

by **ignacio_db** » Fri Nov 13, 2020 7:58 pm

johnnydeep wrote: ↑Fri Nov 13, 2020 7:38 pm
ignacio_db wrote: ↑Fri Nov 13, 2020 5:40 pm
neufer wrote: ↑Fri Nov 13, 2020 5:23 pm
The statement that this "view spans about 2 degrees or 4 full moons" seems rather fishy to me.
The precise FOV is 1d 3' 47.8" x 1d 18' 46.0".

Ignacio
So, this is roughly 1 degree x 1 degree, and not 2 degrees wide per the text? How did you determine the exact field of view?

By plate-solving the image.

Ignacio

by **johnnydeep** » Fri Nov 13, 2020 7:40 pm

rkennaway wrote: ↑Fri Nov 13, 2020 3:32 pm "Formless protoplasm able to mock and reflect all forms and organs and processes — viscous agglutinations of bubbling cells — rubbery fifteen-foot spheroids infinitely plastic and ductile — slaves of suggestion, builders of cities — more and more sullen, more and more intelligent, more and more amphibious, more and more imitative! Great God! What madness made even those blasphemous Old Ones willing to use and carve such things?"

If this site had "recs" I'd give you one for the Lovecraft reference! "At The Mountains Of Madness" indeed: http://www.lovecraft-stories.com/pdf/at ... adness.pdf

by **johnnydeep** » Fri Nov 13, 2020 7:38 pm

ignacio_db wrote: ↑Fri Nov 13, 2020 5:40 pm
neufer wrote: ↑Fri Nov 13, 2020 5:23 pm
APOD Robot wrote: ↑Fri Nov 13, 2020 5:06 am The Tarantula Zone

Explanation: The rich field of view spans about 2 degrees or 4 full moons, in the southern constellation Dorado.
The statement that this "view spans about 2 degrees or 4 full moons" seems rather fishy to me.
The precise FOV is 1d 3' 47.8" x 1d 18' 46.0".

Ignacio

So, this is roughly 1 degree x 1 degree, and not 2 degrees wide per the text? How did you determine the exact field of view?

by **Ann** » Fri Nov 13, 2020 6:32 pm

ignacio_db wrote: ↑Fri Nov 13, 2020 5:21 pm I registered both images against each other, and cropped the SN area with the same geometry. Could it be the red star at the center, sided by two white stars?

Ignacio

: 1987A supernova remnant. Composite of two public domain NASA images taken from the Hubble Space Telescope. See more at https://sv.wikipedia.org/wiki/SN_1987A#/media/Fil:Supernova-1987a.jpg.

Yes indeed, you have found it. Compare your image with the one by the Hubble Space Telescope here. Note the red Hα ring and the two white stars flanking it.

Ann

by **ignacio_db** » Fri Nov 13, 2020 5:40 pm

neufer wrote: ↑Fri Nov 13, 2020 5:23 pm
APOD Robot wrote: ↑Fri Nov 13, 2020 5:06 am The Tarantula Zone

Explanation: The rich field of view spans about 2 degrees or 4 full moons, in the southern constellation Dorado.
The statement that this "view spans about 2 degrees or 4 full moons" seems rather fishy to me.

The precise FOV is 1d 3' 47.8" x 1d 18' 46.0".

Ignacio

by **ignacio_db** » Fri Nov 13, 2020 5:24 pm

Looking further, I think it is: https://www.nasa.gov/sites/default/file ... 3x2000.png

Ignacio

by **neufer** » Fri Nov 13, 2020 5:23 pm

APOD Robot wrote: ↑Fri Nov 13, 2020 5:06 am The Tarantula Zone

Explanation: The rich field of view spans about 2 degrees or 4 full moons, in the southern constellation Dorado.

The statement that this "view spans about 2 degrees or 4 full moons" seems rather fishy to me.

by **ignacio_db** » Fri Nov 13, 2020 5:21 pm

I registered both images against each other, and cropped the SN area with the same geometry. Could it be the red star at the center, sided by two white stars?

Ignacio

by **NCTom** » Fri Nov 13, 2020 4:02 pm

My guess as to location of 1987A is about 4 o'clock from the center of the Tarantula in the middle of a small dark cavity containing two stars one of which is the supernova remnant. When the probe gets there in a million years, we'll know for sure.

by **rkennaway** » Fri Nov 13, 2020 3:32 pm

"Formless protoplasm able to mock and reflect all forms and organs and processes — viscous agglutinations of bubbling cells — rubbery fifteen-foot spheroids infinitely plastic and ductile — slaves of suggestion, builders of cities — more and more sullen, more and more intelligent, more and more amphibious, more and more imitative! Great God! What madness made even those blasphemous Old Ones willing to use and carve such things?"

by **VictorBorun** » Fri Nov 13, 2020 3:15 pm

seems 1987A (bright star to the right and low besides the Tarantula) in 2020 looks dark
https://www.facebook.com/AstronomyPictu ... _tn__=R]-R

by **Tszabeau** » Fri Nov 13, 2020 12:34 pm

It looks angry.

by **orin stepanek** » Fri Nov 13, 2020 12:31 pm

Ann wrote: ↑Fri Nov 13, 2020 6:15 am
Tarantula_HOO_final_2_1024[1].jpg
The Tarantula Nebula with the remnant of SN 1987A.
Photo: Ignacio Diaz Bobillo.

Supernova 1987A (center) at the time of explosion. Photo: ESO - https://www.eso.org/public/images/eso0708a/

So where is the supernova remnant in today's APOD? Can you spot it?

Ann

Ann I'm not good at finding Nova's! The Tarantula doeesn't look like a place I'd like to visit!

Starship Asterisk*

APOD: The Tarantula Zone (2020 Nov 13)

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