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Your M-31 Images Will Continue To Improve....Why?

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#26 entilza

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Posted 18 March 2016 - 08:38 AM

Yes, but the speed of light is a serious limitation. No matter what you do, you will run into that.

 

What no warp drive?? :)


 

#27 Klitwo

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Posted 18 March 2016 - 02:47 PM

If you're going to cross the threshold of deep space to access the outer boundaries of our galaxy...traveling at the speed of light (186,272 miles per second) is 'not' going to cut it....warp drive might possibly do it.  In the mean time, I wouldn't hold your breath too long waiting for science to try and invent a way to travel at the speed of light.  It may never happen. Just to give you an example where we're currently at in terms of our space travel technology....Voyager 1 was launched nearly 40 years ago in 1977 and so far it's cruising along out beyond our solar system at approximately 38,000 miles per hour...For an update on it's mileage...check out: 

 

http://voyager.jpl.nasa.gov/

 

Voyager 1 entered the realm of interstellar space in August 2012, nearly 35 years after blasting off.  As Voyager 1 leaves our solar system behind, the robotic spacecraft is streaking toward an encounter with a star called AC +79 3888 (Gliese 445), a 10.8 apparent magnitude red dwarf star close to Polaris in the constellation Camelopardalis, which lies 17.6 light-years from Earth.  In about 40,000 years Voyager 1 will make a close approach to AC +79 3888 (Gliese 445)...coming within a mere 1.6 light-years of it. (See attached Wikipedia Public Domain photo Images)  It will eventually swing by it and will continue to orbit around the center of our Milky Way galaxy.

 

http://www.space.com...star-flyby.html

 

P.S.  In 40,000 years...those of us humans who are lucky enough to be still be around on planet Earth during the time Voyager 1 is swinging around AC +79 3888 (Gliese 445)...it might be appropriate on or about the year 42016 AD to go ahead and remove the dust cover off of your trusty telescope and depending on our global climate conditions at that time...try and catch a glimpse of the AC +79 3888 (Gliese 445)....and while doing so, perhaps give a hardy salute and a few rounds of whiskey sour cheers to Voyager 1 having made it that far into deep interstellar space since the ancient Earth year of 1977....   

 

Klitwo

Attached Thumbnails

  • AC +79 3888 (Gliese 445).jpg
  • Interstellar Probes.jpg

Edited by Klitwo, 19 March 2016 - 05:10 AM.

 

#28 mvas

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Posted 19 March 2016 - 11:20 AM

I previously assumed the same, but a few years ago, I was summarily educated by Bob Vanderbei.  Interestingly that's not actually the case.  Assuming that M31 is still at a distance that it acts as an extended object (i.e., not individually resolved stars in exposures), then its apparent surface brightness would remain the same.  As the galaxy approaches us, it does become brighter.  However, it also covers a proportionally larger area.  For this reason the mag/arcsec^2 of any given portion remains the same.  Ergo, your required exposure is unchanged.

 

We experience the exact same phenomena in our daily lives.  If you try to take a picture of me standing on a hill a mile away in broad daylight, you might use an exposure of, say 1/200 second at ISO 200 at f/16 (sunny 16 rule).  Now, if I subsequently drive over to your house and stand 10 feet away from you, you'll find that you still need an exposure of 1/200 second at ISO 200 at f/16.  That's despite the fact that I'm over 500 times closer to you.

 

Of course, the sad implication is that, if we were to figure out how to take a rocket flight towards M42, as we got closer to it, it wouldn't become dramatically brighter and start displaying beautiful reds, blues, and greens as the cones in our eyes began responding to colors inherent in the nebula.  No, I'm sorry to say that it would just be a larger (occupying a larger part of the sky) grey blob showing subtle hints of green.  Just like it does from here on good old Terra Firma.

 

In your experiment you used the same exposure, the same ISO and the same f/ratio ( the same lens ?  ) before and after.

But wouldn't your second image now be much, much larger on the CCD Sensor, than your first image?

 

If the Andromeda Galaxy is 10 times closer, then wouldn't the Galaxy now be 10 times bigger on the CCD Imager using the same lens?

 

My idea ...

 

BEFORE

================

Aperture   = 100 mm

F-Ratio     = f/10

FL            = 1,000 mm

ISO          = 200

Exposure = 1/200 sec

 

AFTER

================

Aperture   = 100 mm

F-ratio      = f/1

FL            = 100 mm

ISO          = 200

Exposure = ? sec

 

Using the same size aperture of 100mm,

but now reduce the Focal Length by a factor of 10,

to keep the Image Size on the Sensor the same.

so the f-ratio becomes f/1 vs f/10.

Would an the f-ratio of f/1 then allow the exposure time to be significantly shorter?

 

The two key points in my example are ...

1) Exact same aperture

2) Exact same image size on the sensor by reducing the Focal Length

leads to a faster f-ratio and a shorter exposure ?


Edited by mvas, 19 March 2016 - 11:46 AM.

 

#29 srosenfraz

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Posted 19 March 2016 - 05:09 PM

In your experiment you used the same exposure, the same ISO and the same f/ratio ( the same lens ?  ) before and after.

 

But wouldn't your second image now be much, much larger on the CCD Sensor, than your first image?

 

 

Yes, that is correct.

 

 

 

If the Andromeda Galaxy is 10 times closer, then wouldn't the Galaxy now be 10 times bigger on the CCD Imager using the same lens?

 

True.  And, accordingly, one could expect to be able to resolve details that are 10 times as small (i.e., 10 times as small in actual size - the angular resolution would be unchanged).

 

 

 

My idea ...

BEFORE
================
Aperture   = 100 mm
F-Ratio     = f/10
FL            = 1,000 mm
ISO          = 200
Exposure = 1/200 sec

AFTER
================
Aperture   = 100 mm
F-ratio      = f/1
FL            = 100 mm
ISO          = 200
Exposure = ? sec

Using the same size aperture of 100mm,
but now reduce the Focal Length by a factor of 10,
to keep the Image Size on the Sensor the same.
so the f-ratio becomes f/1 vs f/10.
Would an the f-ratio of f/1 then allow the exposure time to be significantly shorter?

The two key points in my example are ...
1) Exact same aperture
2) Exact same image size on the sensor by reducing the Focal Length
leads to a faster f-ratio and a shorter exposure ?

 

Well, I guess that's true as well.  But, a similar thing could be said for when M31 (or any other object for that matter) is at the same distance - if I change the f/ratio of my optical system from f/10 to f/1, then I would expect to require dramatically less exposure time (and, please - if you know where I can find that 100mm f/1 lens, I'd be most interested - it sounds quite wonderful!).  :-)

 

I don't disagree that when M31 is 10x as close to us that there will be a change - it will certainly occupy 10x the angular diameter and 100x the area in the sky.  I'm sure it'll be quite a spectacular sight.  What I was trying to clarify is that it's easy to assume that it'll start becoming this extremely bright object in the night sky.  The reality is that it'll occupy 100x the area while the total brightness will be 100x as great.  Accordingly, the brightness per area (i.e., the surface brightness) remains the same.  So, at a given f/ratio, it'll require the same exposure as it does today.  And, you're right, at a given focal length, it'll occupy a much larger area on the CCD sensor as well.

 

Hope this helps clarify.


 

#30 Klitwo

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Posted 19 March 2016 - 06:20 PM

 

In your experiment you used the same exposure, the same ISO and the same f/ratio ( the same lens ?  ) before and after.

 

But wouldn't your second image now be much, much larger on the CCD Sensor, than your first image?

 

 

Yes, that is correct.

 

 

 

If the Andromeda Galaxy is 10 times closer, then wouldn't the Galaxy now be 10 times bigger on the CCD Imager using the same lens?

 

True.  And, accordingly, one could expect to be able to resolve details that are 10 times as small (i.e., 10 times as small in actual size - the angular resolution would be unchanged).

 

 

 

My idea ...

BEFORE
================
Aperture   = 100 mm
F-Ratio     = f/10
FL            = 1,000 mm
ISO          = 200
Exposure = 1/200 sec

AFTER
================
Aperture   = 100 mm
F-ratio      = f/1
FL            = 100 mm
ISO          = 200
Exposure = ? sec

Using the same size aperture of 100mm,
but now reduce the Focal Length by a factor of 10,
to keep the Image Size on the Sensor the same.
so the f-ratio becomes f/1 vs f/10.
Would an the f-ratio of f/1 then allow the exposure time to be significantly shorter?

The two key points in my example are ...
1) Exact same aperture
2) Exact same image size on the sensor by reducing the Focal Length
leads to a faster f-ratio and a shorter exposure ?

 

Well, I guess that's true as well.  But, a similar thing could be said for when M31 (or any other object for that matter) is at the same distance - if I change the f/ratio of my optical system from f/10 to f/1, then I would expect to require dramatically less exposure time (and, please - if you know where I can find that 100mm f/1 lens, I'd be most interested - it sounds quite wonderful!).  :-)

 

I don't disagree that when M31 is 10x as close to us that there will be a change - it will certainly occupy 10x the angular diameter and 100x the area in the sky.  I'm sure it'll be quite a spectacular sight.  What I was trying to clarify is that it's easy to assume that it'll start becoming this extremely bright object in the night sky.  The reality is that it'll occupy 100x the area while the total brightness will be 100x as great.  Accordingly, the brightness per area (i.e., the surface brightness) remains the same.  So, at a given f/ratio, it'll require the same exposure as it does today.  And, you're right, at a given focal length, it'll occupy a much larger area on the CCD sensor as well.

 

Hope this helps clarify.

 

 

 

Gentleman......

 

While we're on the subject of M-31 and resolution...let's see what the Hubble Telescope can do on the Andromeda galaxy (M-31)...at least at this point in time.  Click on the image link below for more details.  Resolution-wise...not too shabby...See attached Wikimedia Commons image - (Hubble/ESA - CC BY 3.0)

 

https://en.wikipedia...meda_galaxy.jpg

 

Wouldn't it be interesting if it were possible to compare this image (resolution-wise) as depicted in the Wikimedia link above/below taken by the Hubble Telescope of the Andromeda Galaxy (M-31) in Sept. 2015 compared to a photo image of the Andromeda Galaxy (M-31) taken by the Hubble two billion years from now in the future at the same exact scale, aperture, focal ratio, magnification...etc.  Would you expect to see a difference then when it's approximately 1.25 million light-years away from our galaxy?  I think it would be very obvious.  (Note that when observed slightly magnified in the Hubble Telescope Wikipedia photo...many of the stellar bodies within M-31's star clusters appear to be 'resolved' into individual stars in M-31.....We're talking a distance of approximately 2.5 million light-years....Amazing!)

 

The M-31 Wikipedia website photos demonstrate that the Hubble Telescope can see detail down to 'less' than 0.1 arcsecond across — more than 10 times clearer than what most Earth-based telescopes can image with the same, similar and/or even larger optical apertures....due for the most part because it's well placed for imaging these wonderful galactic objects well above the scintillation effects caused by the Earth's atmosphere....

 

Klitwo

Attached Thumbnails

  • Star Clusters in the Andromeda Galaxy ESA-Hubble_opt.jpg

Edited by Klitwo, 20 March 2016 - 12:05 AM.

 

#31 mvas

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Posted 19 March 2016 - 11:51 PM

 

In your experiment you used the same exposure, the same ISO and the same f/ratio ( the same lens ?  ) before and after.

 

But wouldn't your second image now be much, much larger on the CCD Sensor, than your first image?

 

 

Yes, that is correct.

 

 

 

If the Andromeda Galaxy is 10 times closer, then wouldn't the Galaxy now be 10 times bigger on the CCD Imager using the same lens?

 

True.  And, accordingly, one could expect to be able to resolve details that are 10 times as small (i.e., 10 times as small in actual size - the angular resolution would be unchanged).

 

 

 

My idea ...

BEFORE
================
Aperture   = 100 mm
F-Ratio     = f/10
FL            = 1,000 mm
ISO          = 200
Exposure = 1/200 sec

AFTER
================
Aperture   = 100 mm
F-ratio      = f/1
FL            = 100 mm
ISO          = 200
Exposure = ? sec

Using the same size aperture of 100mm,
but now reduce the Focal Length by a factor of 10,
to keep the Image Size on the Sensor the same.
so the f-ratio becomes f/1 vs f/10.
Would an the f-ratio of f/1 then allow the exposure time to be significantly shorter?

The two key points in my example are ...
1) Exact same aperture
2) Exact same image size on the sensor by reducing the Focal Length
leads to a faster f-ratio and a shorter exposure ?

 

Well, I guess that's true as well.  But, a similar thing could be said for when M31 (or any other object for that matter) is at the same distance - if I change the f/ratio of my optical system from f/10 to f/1, then I would expect to require dramatically less exposure time (and, please - if you know where I can find that 100mm f/1 lens, I'd be most interested - it sounds quite wonderful!).  :-)

 

I don't disagree that when M31 is 10x as close to us that there will be a change - it will certainly occupy 10x the angular diameter and 100x the area in the sky.  I'm sure it'll be quite a spectacular sight.  What I was trying to clarify is that it's easy to assume that it'll start becoming this extremely bright object in the night sky.  The reality is that it'll occupy 100x the area while the total brightness will be 100x as great.  Accordingly, the brightness per area (i.e., the surface brightness) remains the same.  So, at a given f/ratio, it'll require the same exposure as it does today.  And, you're right, at a given focal length, it'll occupy a much larger area on the CCD sensor as well.

 

Hope this helps clarify.

 

 

This was the discussion in message #16

===============================

 

Klitwo said

========

On a much less serious note and 'not' intended to be humorous...but if you were still going to be around for the next three billion years or so...you could expect to see progressively shorter exposure times when imaging M-31.  That possibility should be somewhat encouraging and obviously something to look forward too....however, I wouldn't necessary plan on it unless you've been blessed with 'immortality'.... :waytogo:

 

 

Then you replied

=============

I previously assumed the same, but a few years ago, I was summarily educated by Bob Vanderbei.  Interestingly that's not actually the case

 

 

Then I replied

============

Actually, Klitwo was correct, yes we should expect shorter exposure times when imaging M-31.


 

#32 mvas

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Posted 19 March 2016 - 11:55 PM

 

Gentleman......

 

While we're on the subject of M-31 and resolution...let's see what the Hubble Telescope can do on the Andromeda galaxy (M-31)...at least at this point in time.  Click on the image link below for more details.  Resolution-wise...not too shabby...See attached Wikimedia Commons image - (Hubble/ESA - CC BY 3.0)

 

https://en.wikipedia...meda_galaxy.jpg

 

Wouldn't it be interesting if it were possible to compare this image (resolution-wise) as depicted in the Wikimedia link above/below taken by the Hubble Telescope of the Andromeda Galaxy (M-31) in Sept. 2015 compared to a photo image of the Andromeda Galaxy (M-31) taken by the Hubble two billion years from now in the future at the same exact scale, aperture, focal ratio, magnification...etc.  Would you expect to see a difference then when it's approximately 1.25 million light-years away from our galaxy?  I think it would be very obvious.  (Note that when observed slightly magnified in the Hubble Telescope Wikipedia photo...many of the stellar bodies within M-31's star clusters appear to be 'resolved' into individual stars in M-31.....We're talking about a distance of approximately 2.5 million light-years....Amazing!)

 

It's pretty obvious based on Wikipedia website M-31 photos demonstrates that the Hubble Telescope can see detail down to less than 0.1 arcsecond across — more than 10 times clearer than Earth-based telescopes with the same, similar and in most cases, even larger optical characteristics....due for the most part because it's well placed for imaging these wonderful galactic objects well above the scintillation effects caused by the Earth's atmosphere....

 

Klitwo

 

We can download the raw Hubble and post-process on our own computers.

Would that be an even higher resolution?

 

It has a 2,4000 mm Diameter Mirror and 56,700mm Focal Length ( ~ f/24 ? )

I do not know the Pixel Pitch of any of the CCD imagers

 

The theoretical resolution could be computed, but not by and not now  Zzzzzz.......


Edited by mvas, 20 March 2016 - 12:04 AM.

 

#33 Klitwo

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Posted 20 March 2016 - 01:13 AM

 

 

Gentleman......

 

While we're on the subject of M-31 and resolution...let's see what the Hubble Telescope can do on the Andromeda galaxy (M-31)...at least at this point in time.  Click on the image link below for more details.  Resolution-wise...not too shabby...See attached Wikimedia Commons image - (Hubble/ESA - CC BY 3.0)

 

https://en.wikipedia...meda_galaxy.jpg

 

Wouldn't it be interesting if it were possible to compare this image (resolution-wise) as depicted in the Wikimedia link above/below taken by the Hubble Telescope of the Andromeda Galaxy (M-31) in Sept. 2015 compared to a photo image of the Andromeda Galaxy (M-31) taken by the Hubble two billion years from now in the future at the same exact scale, aperture, focal ratio, magnification...etc.  Would you expect to see a difference then when it's approximately 1.25 million light-years away from our galaxy?  I think it would be very obvious.  (Note that when observed slightly magnified in the Hubble Telescope Wikipedia photo...many of the stellar bodies within M-31's star clusters appear to be 'resolved' into individual stars in M-31.....We're talking about a distance of approximately 2.5 million light-years....Amazing!)

 

It's pretty obvious based on Wikipedia website M-31 photos demonstrates that the Hubble Telescope can see detail down to less than 0.1 arcsecond across — more than 10 times clearer than Earth-based telescopes with the same, similar and in most cases, even larger optical characteristics....due for the most part because it's well placed for imaging these wonderful galactic objects well above the scintillation effects caused by the Earth's atmosphere....

 

Klitwo

 

We can download the raw Hubble and post-process on our own computers.

Would that be an even higher resolution?

 

It has a 2,4000 mm Diameter Mirror and 56,700mm Focal Length ( ~ f/24 ? )

I do not know the Pixel Pitch of any of the CCD imagers

 

The theoretical resolution could be computed, but not by and not now  Zzzzzz.......

 

 

Hello mvas....

 

If you want 'raw' unprocessed Hubble images...you can probably find them in the Hubble Legacy Archive at the following website:

 

http://hubblesite.or...age_processors/

 

See examples of Hubble's excellent resolution of M-31 on this website: 

 

http://ryanmarciniak.com/archives/427

 

P.S. When you get to the last image of M-31 on this website...click a couple of times on each star filled 'box' that highlights a specific star-filled in area in Andromeda....This is Hubble resolution at it's best....

 

Klitwo


Edited by Klitwo, 20 March 2016 - 02:57 AM.

 

#34 srosenfraz

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Posted 20 March 2016 - 07:28 PM



 

This was the discussion in message #16

===============================

 

Klitwo said

========

On a much less serious note and 'not' intended to be humorous...but if you were still going to be around for the next three billion years or so...you could expect to see progressively shorter exposure times when imaging M-31.  That possibility should be somewhat encouraging and obviously something to look forward too....however, I wouldn't necessary plan on it unless you've been blessed with 'immortality'.... :waytogo:

 

 

Then you replied

=============

I previously assumed the same, but a few years ago, I was summarily educated by Bob Vanderbei.  Interestingly that's not actually the case

 

 

Then I replied

============

Actually, Klitwo was correct, yes we should expect shorter exposure times when imaging M-31.

 

 

I'm not trying to be argumentative, but I have to disagree with this conclusion.  Some background - the exposure time needed to obtain a given SNR for an extended object at a given f/ratio is a function of the surface brightness (the amount of light received per area).  If you have an object that has a higher surface brightness, then you can decrease total exposure to achieve a target SNR.  Conversely, if the object has a lower surface brightness, then you can increase total exposure time to achieve the target SNR.

 

However, if the surface brightness remains unchanged, then you will require the same exposure time to achieve a given SNR.  The only way to change that is to change the f/ratio of the system in use (assuming you're using a camera with similar QE, optical system with similiar transmission characteristics, etc.).  For an extended object, the exposure time needed for this level of SNR is not a function of focal length or aperture or any other component - its a function of the f/ratio of the optical system.  Yes, changing the focal length and keeping the aperture will change the f/ratio. And, yes, changing the aperture and keeping the focal length the same will change the f/ratio.  And, yes, if you change aperture and/or focal length to achieve a different f/ratio, you will affect the required exposure time.  But, the driving factor here is that you changed the f/ratio.

 

As I said earlier, I don't have to wait a few billion years to change my f/ratio and capture shorter exposure times to image M31.  I can do that today.

 

The fallacy I see in your statement above ("Actually, Klitwo was correct, yes we should expect shorter exposure times when imaging M-31") is that it implies that M31 will be blazingly bright, thereby necessitating shorter exposures.  That's simply not the case.  It's total magnitude will be brighter (the aggregate of all the light we receive), but it will be spread out over a proportionately larger area.  Accordingly, the time required to image it (and achieve a target level of SNR) with a given optical system will remain unchanged.

 

Siimilarly, if I live in a light polluted city today and have a very difficult time finding M31 with my naked eye, I will have just as hard a time finding M31 from a similarly light polluted city a few billion years in the future.  If I do manage to find it, it will be much, much larger in the sky.  But, it'll still be a faint fuzzy.

 

(paraphrasing Dennis Miller) Of course, I'm just an amateur astrophotographer. I could be wrong....


Edited by srosenfraz, 20 March 2016 - 07:53 PM.

 

#35 whwang

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Posted 22 March 2016 - 07:58 PM

 

I'm not trying to be argumentative, but I have to disagree with this conclusion.  Some background - the exposure time needed to obtain a given SNR for an extended object at a given f/ratio is a function of the surface brightness (the amount of light received per area).  If you have an object that has a higher surface brightness, then you can decrease total exposure to achieve a target SNR.  Conversely, if the object has a lower surface brightness, then you can increase total exposure time to achieve the target SNR.

 

 

This statement is correct only if you change "SNR for an extended object" to "SNR per unit solid angle" (such as SNR per sq-arcsec).  These are two completely different concepts.

 

When we say SNR for an object (extended or not), we mean the total SNR integrated over the entire object.  Then under the condition of constant surface brightness, the SNR of an object is proportional to its linear size on the sky.  If you only want a fixed SNR over that object, then you can decrease integration time when the object is bigger.

 

Cheers,

Wei-Hao


 

#36 srosenfraz

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Posted 22 March 2016 - 10:14 PM

Hi Wei-Hao -

 

When I zoom into my image and look at the noise of my M31 in the faint outer halo, am I not effectively evaluating the SNR per arcsec^2?  In other words, isn't the appearance of noise in any given portion of the image reflective of the SNR per arcsec^2 (or whatever unit of area you wish to use)?


 

#37 Klitwo

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Posted 22 March 2016 - 10:25 PM

Kudos to NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger for their excellent view of the Andromeda galaxy 7 billion years from now......Enjoy!

 

http://www.planetary...2/06041013.html

 

 

'When you setup your trusty telescope tonight to observe the Andromeda galaxy (M-31)...remember it's approaching our galaxy the Milky Way approximately 250,000 miles per hour.  This means when you're observing it tonight...it will be about 6,000,000 miles closer than when you observed it at the same time the previous night'...

 

And with that thought in mind...there aren't too many celestial objects out there...especially extended celestial objects that you can say that about.  The Andromeda galaxy is an 'exception'....

 

Klitwo


Edited by Klitwo, 23 March 2016 - 05:54 PM.

 

#38 whwang

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Posted 22 March 2016 - 11:09 PM

Hi Wei-Hao -

 

When I zoom into my image and look at the noise of my M31 in the faint outer halo, am I not effectively evaluating the SNR per arcsec^2?  In other words, isn't the appearance of noise in any given portion of the image reflective of the SNR per arcsec^2 (or whatever unit of area you wish to use)?

 

That's right.  When we examine an image in detail and feel the "noise," we are seeing SNR per arcsec^2.  We just shouldn't call it "SNR of an object."  It's SNR of whatever unit area that's appropriate for the viewing condition.  

 

For M31, I guess the total SNR for the galaxy is many thousands (if not millions) in a decent picture.


 

#39 srosenfraz

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Posted 23 March 2016 - 08:55 AM

Thank you for the clarification.


 

#40 mvas

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Posted 26 March 2016 - 02:27 PM

I'm not trying to be argumentative, but I have to disagree with this conclusion.  Some background - the exposure time needed to obtain a given SNR for an extended object at a given f/ratio is a function of the surface brightness (the amount of light received per area).  If you have an object that has a higher surface brightness, then you can decrease total exposure to achieve a target SNR.  Conversely, if the object has a lower surface brightness, then you can increase total exposure time to achieve the target SNR.

 

However, if the surface brightness remains unchanged, then you will require the same exposure time to achieve a given SNR.  The only way to change that is to change the f/ratio of the system in use (assuming you're using a camera with similar QE, optical system with similiar transmission characteristics, etc.).  For an extended object, the exposure time needed for this level of SNR is not a function of focal length or aperture or any other component - its a function of the f/ratio of the optical system.  Yes, changing the focal length and keeping the aperture will change the f/ratio. And, yes, changing the aperture and keeping the focal length the same will change the f/ratio.  And, yes, if you change aperture and/or focal length to achieve a different f/ratio, you will affect the required exposure time.  But, the driving factor here is that you changed the f/ratio.

 

As I said earlier, I don't have to wait a few billion years to change my f/ratio and capture shorter exposure times to image M31.  I can do that today.

 

The fallacy I see in your statement above ("Actually, Klitwo was correct, yes we should expect shorter exposure times when imaging M-31") is that it implies that M31 will be blazingly bright, thereby necessitating shorter exposures.  That's simply not the case.  It's total magnitude will be brighter (the aggregate of all the light we receive), but it will be spread out over a proportionately larger area.  Accordingly, the time required to image it (and achieve a target level of SNR) with a given optical system will remain unchanged.

 

Siimilarly, if I live in a light polluted city today and have a very difficult time finding M31 with my naked eye, I will have just as hard a time finding M31 from a similarly light polluted city a few billion years in the future.  If I do manage to find it, it will be much, much larger in the sky.  But, it'll still be a faint fuzzy.

 

(paraphrasing Dennis Miller) Of course, I'm just an amateur astrophotographer. I could be wrong....

 

 

You said, "... is that it implies that M31 will be blazingly bright ..."

No, I did not say, nor did I imply, that the M-31 would be blazing bright.

 

I said, that M-31 would be increasing larger.

 

As the size increases, we must use a shorter a focal length, to get the exact same sized image on the ccd/cmos chip.

A shorter focal length, with the same aperture (light collecting power) equals a faster f/ratio.

A faster f/ratio will lead to a shorter exposure time.

This is what happens when an object gets closer and you want the exact same sized image on the ccd/cmos chip.

 

You are talking about taking an image that is a progressively smaller and smaller and smaller and smaller and smaller portion of M-31, as it gets closer.

HUH?

That is not what I call, taking the same image of M-31.

 

When M-31 is 16X's closer, I can and will use 1/16th the Focal Length, with same aperture, to get the exact same sized image on the ccd/cmos chip.

No, it is not possible for you to change your f/ratio today, while maintaining the same aperture, and get the exact same sized image on the ccd/cmos chip.

 

I am talking about taking the exact same sized image of Andromeda, as measured on the chip, as it gets closer and closer.

 

REAL WORLD EXAMPLE

=====================

If I have a 4" @ f/10 and M-31 just fills the imager chip today

then when M-31 is twice as close I must reduce the 4" to f/5 to have M-31 just fill the imager.

This faster f/ratio is a shorter exposure time.

1) Keeping 4" the same, means using the same light collection power.

2) Keeping the size of the object on the imager,  means taking the same image

 

You are talking about taking a progressively different image of M-31, as it gets closer.

And eventually, your image will not even fit on the imager.

Is that you definition of "taking the same image of Andromeda, as it gets closer?"

 

 

When a person is real far from you and you take their photo with telephoto,

then when they are much closer to you,

do you still use the same telephoto focal length

and now take a very zoomed-in photo of just their shoe

and call that "the same photo of the person?"

I don't.


Edited by mvas, 26 March 2016 - 02:35 PM.

 

#41 Klitwo

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Posted 02 April 2016 - 02:03 AM

Just think...When this thread was first started on Feb. 26, 2016....the Andromeda galaxy (M-31) has moved about 222,000,000 miles closer to us.....I know it doesn't sound like much in astronomical terms...but in 3.75 billion years from now...if the future humans or what's left of them are still lucky enough to be around....they might want to take a quick look in the evening sky to check it out....I hope they kept that extra heavy-duty air conditioner running on high...They're going to need it...Charcoal Broil Big Time!

 

Klitwo


Edited by Klitwo, 02 April 2016 - 02:49 AM.

 

#42 Kstevens

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Posted 02 April 2016 - 01:11 PM

 Frank Drake's equation developed in 1961 which has been used in everything from SETI to StarTrek:

 

N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.

 

N = R* • fp • ne • fl • fi • fc • L

 

R* =The rate of formation of stars suitable for the development of intelligent life.

fp = The fraction of those stars with planetary systems.

ne = The number of planets, per solar system, with an environment suitable for life.

fl = The fraction of suitable planets on which life actually appears.

fi = The fraction of life bearing planets on which intelligent life emerges.

fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

L = The length of time such civilizations release detectable signals into space.

 

and then Sara Seger revised the Drake equation:

 

N = the number of planets with detectable signs of life

 

N = N* • FQ • FHZ • FO • FL • FS

 

N* = the number of stars observed

FQ = the fraction of stars that are quiet

FHZ = the fraction of stars with rocky planets in the habitable zone

FO = the fraction of those planets that can be observed

FL = the fraction that have life

FS = the fraction on which life produces a detectable signature gas

 

So the question is in the far future extents of our civilization, who will be observing who and from where and when?


Edited by Kstevens, 02 April 2016 - 01:20 PM.

 

#43 Klitwo

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Posted 05 April 2016 - 12:17 PM

The famous 'Drake Equation' seems to indicate that at least one life form does actually 'exist' on one planet in our galaxy...Earth!  Kudos to Frank Drake.

 

Klitwo


Edited by Klitwo, 06 April 2016 - 04:03 AM.

 

#44 Klitwo

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Posted 13 May 2016 - 04:43 AM

This is just a short reminder for those of us who observe M-31 regularly through our trusty telescope.  Those who do will be happy to hear that the Andromeda galaxy has moved approximately 528,000,000 miles closer to our solar system since the start of this thread on Feb. 16, 2016.  Maybe it might be a good time to start thinking about dusting off the old lawn chair, camera and tripod in eager anticipation of getting a good view of this far in the future super-colossal cosmic event...the collision of the Andromeda galaxy (M-31) with our Milky Way galaxy in the next 3.75 billion years.  Never to early to plan....especially for those calendar watchers who were lucky enough to have been blessed with immortality!  And for those of us who weren't?....at least we'll save some $$$ on sun screen..!

 

Klitwo


Edited by Klitwo, 13 May 2016 - 02:43 PM.

 

#45 Tonk

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Posted 14 May 2016 - 06:30 AM

"our two galaxies are already in contact with each other"

 

Hummm - according to that diagram the Milkyway doesn't have a halo - that's way too strange. Surely the halo map the researchers have measured is a projection of the union of halo's of both the Milkyway and M31


 

#46 Klitwo

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Posted 31 May 2016 - 01:00 AM

The Milky Way's halo according to NASA....See link below.

 

http://www.nasa.gov/...t_gas_halo.html

 

 

Klitwo


 

#47 Klitwo

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Posted 03 June 2016 - 03:54 AM

Just think...When this thread was first started on Feb. 26, 2016....the Andromeda galaxy (M-31) has moved about 222,000,000 miles closer to us.....I know it doesn't sound like much in astronomical terms...but in 3.75 billion years from now...if the future humans or what's left of them are still lucky enough to be around....they might want to take a quick look in the evening sky to check it out....I hope they kept that extra heavy-duty air conditioner running on high...They're going to need it...Charcoal Broil Big Time!

 

Klitwo

An update....

 

Add another 61 days (366,000,000 miles) to the total from the last post on April 2, 2016 and it looks like M-31 has travelled about 588,000,000 miles closer to our Milky Way galaxy since this thread was first started on Feb. 26, 2016.  Still perhaps a little early yet to be breaking out the sun screen, lawn chairs and chilling down those "6-packs" in anticipation of watching this anxiously awaited far in the future cosmic event. 

 

P.S.  We may even end up with a bonus too...M-33, Andromeda's companion galaxy may pile into our Milky Way galaxy first adding even more cosmic disorder to the final collision....Now that's something to really look forward to...a three way galactic crash!  It doesn't get any better than that folks.

 

 

http://www.nasa.gov/...ay-collide.html

 

 

http://phys.org/news...lion-years.html

 

 

 

Klitwo


Edited by Klitwo, 04 June 2016 - 02:28 AM.

 

#48 Klitwo

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Posted 02 July 2016 - 09:38 PM

Another mileage update for the serious M-31 collision watchers out there....M-31 is approximately 768,000,000 miles closer to our Milky Way galaxy since the thread was originally posted on Feb. 26, 2016. Not quite close enough to break out the lawn chairs, potato chips and cold beer yet...but certainly a super-cosmic event to plan for if you are still planning to be around some 4 billion years from now...

Klitwo


Edited by Klitwo, 03 July 2016 - 03:46 AM.

 

#49 Klitwo

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Posted 17 July 2016 - 11:59 PM

An Update.  Some good news for the M-31/Milky Way collision calendar watchers out there!  Hold on to your seat belts....M-31 may collide with the Milky Way much sooner than expected.  It's still probably just a little bit too early yet to start dragging out those cozy lawn chairs, cleaning out the beer cooler, dusting off the old binoculars, breaking out the new barbecue grill and installing an extra heavy-duty air conditioner.  The majority of us cannot help to envy those who (if any) will still be around in the next four billion years to watch this long awaited fantastic future cosmic event unfold in our night sky....However at this point in time...it's probably a good bet that ticket prices are pretty cheap!  See attached link for details.

 

 

http://www.telegraph...n-expected.html

 

 

Klitwo


Edited by Klitwo, 18 July 2016 - 09:23 PM.

 

#50 Klitwo

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Posted 02 August 2016 - 08:59 PM

 

"our two galaxies are already in contact with each other"

 

Hummm - according to that diagram the Milkyway doesn't have a halo - that's way too strange. Surely the halo map the researchers have measured is a projection of the union of halo's of both the Milkyway and M31

 

 

The Milky Way does indeed have a large halo alright...and it's very hot and spinning very fast....See following link

 

http://www.space.com...ying-speed.html

 

 

Klitwo


 


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