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How to Conceptualize Magnification?

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#1 Neil Sanford

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Posted 18 November 2019 - 03:25 AM

I have a bunch of binos that I use about 50/50 terrestrial and on the night sky.  For years I was only terrestrial, and have found it easy to think of terrestrial magnification like this: 

Say my bino is 7x and I am looking at a target 7 miles away.  Then I see that target, compared to my naked eye, 7 times bigger.  Or (I like this one better) that target seems instead of 7 miles distant, only 1 mile. 

 

But I have difficulty conceptualizing astronomical magnification in a down-to-earth way that my brain can intuit.  Take Rigel, distance in light years ~1400.  Since we want our binocular view of stars, at all magnifications, to be as pinpoints, it makes no sense to achieve a 7 times bigger pinpoint.  And it seems not very helpful to say that a 7x bino lets you see Rigel as if distant only 200 light years.  That’s not like viewing a 7-mile distant mountain, then walking 6 miles closer to see it from 1 mile ...  or saving the walk and using a 7x bino.

 

On earth it makes sense (to me) to think of magnification as bigger or closer.  On the night sky, probably it makes sense to think of binocular magnification as brighter, as in we can see stars of lesser magnitude, or any given star takes on a brighter magnitude—say at 7x Rigel goes from apparent mag ~.12 to ~.017.  I guess that’s okay.   Except just as bigger and closer don’t help in thinking about astro magnification, brighter doesn’t translate to terrestrial magnification.  It doesn’t make sense to think of that mountain as 7 times brighter. 

 

I am okay with this much, don’t feel a need to seek therapy about it.  Still, your thoughts most welcome.



#2 siriusandthepup

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Posted 18 November 2019 - 05:03 AM

Closer is the better way to think of it.

 

Take the Moon for a popular example (you are correct - the stars look the same no matter the mag) call it 240,000 miles away..

 

magnify 1000x - now it looks the way it would from 240 miles away.

 

magnify 10,000x - now it looks 24 miles away.

 

Assume we have perfect seeing (yeah - right - that's gonna happen). Now ask your self - can you see a school bus naked eye at 24 miles? I don't think so. If you can't see a school bus at 24 miles away at 10,000x and perfect seeing, then you have no prayer of seeing the Apollo landing site.

 

Also, one way the stars do look different with magnification is that when you are closer to objects you get higher resolution - increased ability to see details - Example here close double stars.

 

So I vote "closer" as the better way to picture it.


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#3 Thomas Marshall

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Posted 18 November 2019 - 05:09 AM

I like thinking the distance is 'actually and literally closer' at  the various power ranges, - so if I'm seeing what happened 100 light years ago with naked eyes, - @100 power thru scope, I'm skipping closer up the beams of light, to only 1 light years distance, and I'm getting a much more current input of what's going on Now with that star. - Kind of like a history tour in reverse. 100 years ago/75 years ago/50 years ago/25 years ago/1 year ago. I'm pretty sure, that in the starbeams, it's not just viewing 100 years in the past, or whatever else it's distance, - but that it is All There, - past/present/ and future. Don't ask me to prove it, or to quit dreaming and sober up. grin.gif A diamond crystal can be 3 billion years old, and look pristine new, and yet it holds  All 3 billion years of it's history with it. It is not just an image of what it was 3 billion years ago, it's what it is/was every day of those last 3 billion years. And how much more is a star, - than a diamond crystal?wink.gif



#4 Mark9473

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Posted 18 November 2019 - 05:38 AM

There are many cool aspects about astronomical viewing.

The most obvious one, even without thinking about distances, is that objects other than stars take up a larger size in our visual field of view.

For stars in particular, I like that binoculars make the ordinary stars making up constellations look as bright or brighter than the brightest stars visually, and some even brighter than the planets visually.

 

What I find most awesome is to think about the size of the observable universe. I don't think of that as a sphere, as an object's visibility depends on its absolute brightness and not just its distance. Looking up at the sky I imagine a line connecting me to every visible star - thousands of lines converging on me, all of different length, most only some tens or hundreds of light years long, or some thousands to the larger clusters and clouds of the Milky Way, but if I'm lucky and the Andromeda galaxy is visible then there's one that's 2.5 million light years long...

Now using binoculars gives me, in a small area of sky, a much larger density of those lines-of-sight and potentially many of those really long ones. Sweeping the binoculars around, imagine all tones lines disconnecting and new ones instantly connecting.


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#5 Jon Isaacs

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Posted 18 November 2019 - 06:14 AM

A star is a point of light so it never gets larger with magnification.

 

But the separation between two stars increases with magnification and objects like galaxies, clusters, nebulae, the planets, these all increase in size proportional to the magnification.

 

Your example of Rigel is a good one, Rigel has magnitude 10.4 companion about 9 arc-seconds distant that is relatively easy to see (in a telescope) with enough magnification.

 

Otherwise, as others have suggested, magnification can be thought of just as it is terrestrially, seeing the object as if it were closer to you. In 10 x 70 binoculars stars will be 100 times brighter than a 7mm dark adapted pupil.. Rigel would 100 times brighter than naked eye. 

 

Extended objects will not be brighter but they will be proportionally larger.  M42 will be just as bright but 10 times as large, just as if you were 10 times closer. 

 

Jon


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#6 eyespy

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Posted 18 November 2019 - 12:48 PM

Hi Neil. 

 

With the the moon and the brighter larger planets I tend to to think in terms of magnification. For all other objects in the night sky I prefer to think in terms of the degree size field of the binoculars. Astronomical distances are so great that how close they appear in binoculars becomes somewhat mute. 

 

Doug....


Edited by eyespy, 18 November 2019 - 12:52 PM.


#7 Sketcher

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Posted 18 November 2019 - 12:56 PM

Conceptualize it as it is:

 

Increased magnification = larger apparent angular size.

Decreased magnification = smaller apparent angular size.



#8 KennyJ

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Posted 18 November 2019 - 02:02 PM

I have been known to look at the moon through 10x binoculars backwards, so I can get an idea what it would look like if it were around 2.4 million miles away, rather than just across the sky at 240,000 miles, or if you like, make it appear as if the moon were ten times smaller than it really is.

 

Any less than MINUS TWENTY times magnification makes the moon almost disappear into a barely distinguishable dot.


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#9 Jon Isaacs

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Posted 18 November 2019 - 02:06 PM

I have been known to look at the moon through 10x binoculars backwards, so I can get an idea what it would look like if it were around 2.4 million miles away, rather than just across the sky at 240,000 miles, or if you like, make it appear as if the moon were ten times smaller than it really is.

 

Any less than MINUS TWENTY times magnification makes the moon almost disappear into a barely distinguishable dot.

 

I have done this looking at the moon but generally found it unsatisfying.

 

I generally reserve this technique for looking at politicians where it is most rewarding.. :)

 

Jon


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#10 oldmanrick

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Posted 18 November 2019 - 06:32 PM

I like thinking the distance is 'actually and literally closer' at  the various power ranges, - so if I'm seeing what happened 100 light years ago with naked eyes, - @100 power thru scope, I'm skipping closer up the beams of light, to only 1 light years distance, and I'm getting a much more current input of what's going on Now with that star. - Kind of like a history tour in reverse. 100 years ago/75 years ago/50 years ago/25 years ago/1 year ago. I'm pretty sure, that in the starbeams, it's not just viewing 100 years in the past, or whatever else it's distance, - but that it is All There, - past/present/ and future. Don't ask me to prove it, or to quit dreaming and sober up. grin.gif A diamond crystal can be 3 billion years old, and look pristine new, and yet it holds  All 3 billion years of it's history with it. It is not just an image of what it was 3 billion years ago, it's what it is/was every day of those last 3 billion years. And how much more is a star, - than a diamond crystal?wink.gif

grin.gif I respectfully disagree.  You are not "skipping closer up the beams of light", to see a more current picture of what's going on at your target.  To do this you would have to be accelerating the speed of light beyond what Albert Einstein said is possible, and thus warping time.  This may someday be possible, but our optical instruments can't do it.

 

When we magnify the image of a planet, star, DSO, or whatever, we are only enlarging our view of that beam of light when it arrives at our viewing instrument.  It is still a representation of how that target looked however long ago it was when that beam of photons started on the journey to our instrument.  The magnification factor is only stating how much we are magnifying the image carried by that beam of light, compared to viewing it with our naked eyes.

 

Rick



#11 Thomas Marshall

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Posted 19 November 2019 - 02:51 AM

grin.gif I respectfully disagree.  You are not "skipping closer up the beams of light", to see a more current picture of what's going on at your target.  To do this you would have to be accelerating the speed of light beyond what Albert Einstein said is possible, and thus warping time.  This may someday be possible, but our optical instruments can't do it.

 

When we magnify the image of a planet, star, DSO, or whatever, we are only enlarging our view of that beam of light when it arrives at our viewing instrument.  It is still a representation of how that target looked however long ago it was when that beam of photons started on the journey to our instrument.  The magnification factor is only stating how much we are magnifying the image carried by that beam of light, compared to viewing it with our naked eyes.

 

Rick

Of course Rick, - but there is some tongue and cheek in my post also, and I  think you and many are not giving light it's due. It's speed varies thru different mediums, and is I believe less finite than people know. Also, speed is only 1 of it's properties, and lesser than some of it's other attributes. An image magnified, would just be bigger, with no increased resolution, as in enlarging a photo, but light is more than image only, or a carrier of images, and keeps it's fidelity however close or far you look at it from. Some even think there is "living light" with it's own capabilities and will. But, my 1st post was mainly the musings of a "recreational astronomer", and I'm not trying to troll anyone or set forth any thesis. cool.gif



#12 ihf

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Posted 19 November 2019 - 03:02 AM

I don't like the concept of walking closer to a mountain, as this does not honor the perspective (going from tele to wide angle). I think of magnification as compression of space in the depth direction. The perspective flattening of the landscape at 18x is incredible. I find it intuitive that points (zero area) become brighter, while areas stay constant in brightness. To achieve this telescopes/binocular need to remove a lot of incoming light (not contributing to the magnification). At high magnifications they are near perfect light destruction devices!



#13 PEterW

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Posted 19 November 2019 - 04:05 AM

It’s all about angles, though for terrestrial distance can be a more convenient way to think about it. Stars are not truly point sources, though the diffraction limits of most scopes and the turbulence of the atmosphere make it impossible to see. Many close or large stars have had their diameters measured and even things like sunspots seen/inferred. Of course this is beyond where binoculars can go.

Peter
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#14 Jon Isaacs

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Posted 19 November 2019 - 06:33 AM

Peter:

 

Betalgeuse has a diameter of about 0.05"   That's the diameter to the first minima of the Airy disk of of a 5.5 meter aperture.

 

I think I can safely say that no person has ever looked through an eyepiece and resolved the disk of a star. For all practical purposes, to visual astronomers, stars are points of light.

 

Analytically it is about angles. But concepts are a different thing and the concept that a telescope brings you closer is a powerful and useful concept..

 

Jon


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#15 FDR

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Posted 19 November 2019 - 10:38 AM

For any stars through most binoculars (all handhelds), even the largest/closest stars will still be pin points. It's like looking down a laser beam 7 miles out. 7x binoculars will make a 0.1 inch pinpoint look like a 0.1 inch source at 1 mile out, which will still be a pinpoint. The pinpoint will be brighter though (don't test this with a laser). It's not quite the same as most terrestial objects because it's emitting light, not just reflecting it

 

Besides the moon and sun, I don't think there are any individual objects you can reasonably size-up by the naked eye unless you're at a true dark site (maybe). The Pleiades cluster visible from the northern 2/3 of Earth may help since it fits nicely in binoculars. Using 7x binoculars to compare, the cluster will appear 7x wider. The larger lens will be able to collect more light, so the right conditions will allow you to see some of the nebulosity by being a brighter image, not just magnified


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#16 tmichaelbanks

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Posted 19 November 2019 - 11:03 AM

It's not often I feel I can bring something of substance to a CN thread, but I am definitely in the "magnification as reducing distance" camp here in that more magnification is like being closer, even if you are looking through a straw.  This is especially the case for extended objects as we know, but even some stars are not so small or far away that they can't appear as extended objects.

 

It takes a huge telescope like the Hubble, but stars other than the Sun have been photographically imaged as extended objects.  For closeup views of Betelgeuse and Mira A, see the Astronomy Picture of the Day website links at:

 

https://apod.nasa.go...d/ap990605.html

(first image of Betelgeuse obtained)

 

https://apod.nasa.go...d/ap100106.html

(cheating a little, as this is an infrared interferometric image of Betelgeuse, not a direct visual image, but intriguing nonetheless)

 

https://apod.nasa.go...d/ap981011.html

(this image of Mira A shows what appears to be a stream of glowing matter, perhaps connecting it to its white dwarf companion)

 

And only a 7-foot 10-inch mirror!  But of course, there's no substitute for good seeing and a steady mount (or attitude control system).  grin.gif


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#17 Keudn

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Posted 19 November 2019 - 12:11 PM

There haven't been a ton of helpful answers in this thread, so I'll take a shot at explaining it. What telescopes and binoculars do is take a section of the sky and focus that image. The eyepiece then takes that focused light and aligns it parallel again. When you put your eye up to the eyepiece, what you see is that area of the sky projected in front of you. The reason it looks bigger and thus magnified is because instead of that section of the sky taking up say a 1° x 1° area of your view in the sky, it now fills almost your entire field of view when seen through the eyepiece. You can see this with the picture below. Note that the image as illustrated might make you think it is making the object look smaller, it isn't. Think of it as literally taking a square in the sky and blowing it up bigger in front of you.

http://www.math.ubc....ng/refract1.jpg



#18 Pinac

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Posted 19 November 2019 - 12:29 PM

But isn‘t there an even simpler explanation?

 

I think the only thing telescopes (and binoculars) do:

 

they increase the angle under which we see an object, a landscape or a section of the sky., compared to the angle under which we see it with the naked eye.

 

That‘s why we think we have moved closer to the object, landscape or sky section.

 

Isn‘t that what it is?

 

Pinac


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#19 Neil Sanford

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Posted 20 November 2019 - 02:18 AM

Wow.  This is great.  What a curious, collaborative (respectful), enlightening conversation.  (Though not intended, this reminds me of early years in this Forum, when extensive fundamental understandings were being developed.)  From this OP, all above replies much appreciated.


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#20 charlesgeiger

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Posted 20 November 2019 - 03:03 AM

If you are looking at an extended object (the full moon for instance which is about 30 arc seconds in diameter on the sky naked eye) with 10X magnification, the instrument giving you the 10X will make the moon look like it is 300 arc seconds in diameter.  So with the naked eye, the moon appears 30 arc minutes in diameter which is 1/2 degree.  So 300 arc minutes in the instrument would look like naked eye 5 degrees.  This same analogy can be used with clusters, extended nebulae, the planets, etc.  So the individual stars will not have any enlargement but the entire cluster or extended object will.  

I believe this is the correct analogy.  

Charlie



#21 Tony Flanders

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Posted 21 November 2019 - 07:19 PM

Closer is the better way to think of it.
 
Take the Moon for a popular example ...


That works well for me for the Moon, but not for any other celestial object. That's because the Moon is the only celestial object at a distance that's really graspable in terms of everyday life. If there was a highway and plenty of gas stations, you could drive there in a year, with time off to sleep every night.
 
But when you get to the Sun, I can't visualize the distance the same way. I can work with it; I know the scale of the solar system by heart; it all makes sense in that context. But it's an entirely different scale from the one where we live our lives -- and even more different from the one that stars and galaxies live on. If you bring the Sun 100 times closer it's still much farther than the Moon, and there's precious little in between. If you bring Sirius 100 times closer, it's much farther than Pluto, and there's really little in between.

 

Speaking of scales, I still find it amazing to think that if Earth was in the center of the Sun, the Moon's orbit would all be deep inside the Sun. Yikes!


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#22 jaraxx

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Posted 21 November 2019 - 09:26 PM

I like thinking the distance is 'actually and literally closer' at  the various power ranges, - so if I'm seeing what happened 100 light years ago with naked eyes, - @100 power thru scope, I'm skipping closer up the beams of light, to only 1 light years distance, and I'm getting a much more current input of what's going on Now with that star. - Kind of like a history tour in reverse. 100 years ago/75 years ago/50 years ago/25 years ago/1 year ago. I'm pretty sure, that in the starbeams, it's not just viewing 100 years in the past, or whatever else it's distance, - but that it is All There, - past/present/ and future. Don't ask me to prove it, or to quit dreaming and sober up. grin.gif A diamond crystal can be 3 billion years old, and look pristine new, and yet it holds  All 3 billion years of it's history with it. It is not just an image of what it was 3 billion years ago, it's what it is/was every day of those last 3 billion years. And how much more is a star, - than a diamond crystal?wink.gif

I'm going to have to drink for awhile, then I'll read this again...


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#23 Thomas Marshall

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Posted 22 November 2019 - 01:41 AM

I'm going to have to drink for awhile, then I'll read this again...

Cheers!cool.gif



#24 ihf

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Posted 22 November 2019 - 12:11 PM

I think Toni makes an excellent point about scale. The moon (and the planets!) are at a distance compared to their size that still permits a bit of depth perception. In other words the distance of the observer/earth to the objects really matters and depth of detail might (just might?) be perceived under magnification. That is why I mentioned "compression of space" (or volume). Now except for planets (and a few moons, comets) everything else is insignificant in size compared to their distance. Whatever equipment and magnification amateurs throw at them they remain points (not just the diffraction limit of the instrument, but also limited by the eye). We see those objects (stars, small moons, asteroids) not because they extend in area and cover a volume, but simply because they are bright enough to send energy into our receptors. As their size does not respond to any magnification (and also I think because there is usually only empty space between us and the objects) we can simplify the situation and think of them as being points on a two-dimensional plane. Because of projection this plane can be equally thought of being at infinity, or on a piece of paper a few inches away. And here I feel the problem of astronomic magnification leaves the realm of our immediate three-dimensional experience and becomes an abstract and imperfect analogy. (I think of them as being drawn on a sheet of thin rubber that I can stretch.)



#25 Jon Isaacs

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Posted 24 November 2019 - 06:44 AM

I think Toni makes an excellent point about scale. The moon (and the planets!) are at a distance compared to their size that still permits a bit of depth perception. In other words the distance of the observer/earth to the objects really matters and depth of detail might (just might?) be perceived under magnification. That is why I mentioned "compression of space" (or volume). Now except for planets (and a few moons, comets) everything else is insignificant in size compared to their distance. Whatever equipment and magnification amateurs throw at them they remain points (not just the diffraction limit of the instrument, but also limited by the eye). We see those objects (stars, small moons, asteroids) not because they extend in area and cover a volume, but simply because they are bright enough to send energy into our receptors. As their size does not respond to any magnification (and also I think because there is usually only empty space between us and the objects) we can simplify the situation and think of them as being points on a two-dimensional plane. Because of projection this plane can be equally thought of being at infinity, or on a piece of paper a few inches away. And here I feel the problem of astronomic magnification leaves the realm of our immediate three-dimensional experience and becomes an abstract and imperfect analogy. (I think of them as being drawn on a sheet of thin rubber that I can stretch.)

 

There are many, many objects whose size is significant in relation to their distance.  Depth perception is based on the distance to the object versus the baseline, no astronomical object is close enough for an observer to experience true depth perception. They're all at infinity.

 

The moon and the planet's are not the largest objects visible in the night sky, there are numerous nebulae and galaxies that are larger.  A search with Sky Safari Pro shows about 700 nebulae, galaxies and globular clusters larger than 0.5 degrees, the size of the moon. There are over 10,000 larger than the largest planet. M57, the ring nebula, is 1.4' x 1.1', larger than all the planets. 

 

Binoculars and telescopes do not increase the surface brightness of an extended object, it will never be brighter than naked eye. They make them larger so the eye can see them.

 

But even a small extended object will become larger with magnification.  This is as one expects when moving closer.

 

Open clusters are collections of stars, the stars become brighter (With an appropriate exit pupil) and more widely separated. Single stars become brighter. This as is expected when one moves closer. 

 

When I look at the Night Sky at 80 x with a 7 mm exit pupil, it really does look like it would naked eye if it were 80 times closer.

 

Jon


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