Andromeda and the Moon (no photos)

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dalethorn

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In the below link NASA has photos of sections of Andromeda that show the individual stars. A star bigger than the Sun (1 million mile diameter) would be 15 trillion times its diameter distant from Earth (2.5 million LY times 6 trillion miles per LY). A Moon rover or LEM, if 8 feet long, would be ~150 million times its length distant from Earth. That's 100 thousand times closer in photographic perspective than those stars. So if I allowed even a 100 times fudge factor in the comparison, the Moon objects should resolve a thousand times better linearly than the Andromeda stars. A fudge factor might be seeing a star's light photons, but not the star, although looking at the Hubble image it seems they do see the stars somehow.

So anyway, I haven't seen any high-res photos of our rovers or flags sitting on the moon after all these years.

Hubble’s High-Definition Panoramic View of the Andromeda Galaxy
 
It turns out according to NASA that the smallest object we can see on the moon from Earth is 328 feet wide/high, which means that the current best resolution is 100 to 300 times less than needed to resolve those objects. So applying that to Andromeda the resolution needed there is about 10 million times too little in any dimension. And yet they say that those stars are resolved...
 
Just pondering these perspectives - since a Sun-like star in Andromeda is ~600 billion times its diameter distant (too small to see with anything), how about a galaxy near the edge of the observable universe? We know that Andromeda is about 7 times wider in the night sky than the full moon, so that's a huge target for a time exposure. A galaxy at the edge of the visible universe would be about 5000 times farther away than Andromeda, or about 125000 times its diameter (100k LY) distant. On the Moon we can resolve an object that's 3.8 million times its diameter distant. That should mean that the most distant galaxies, if they're the size of the Milky Way or Andromeda and in a favorable viewing angle, will be about 30 times bigger than the minimal viewing size. But given the actual astro-photos I've seen from the Deep Field series, the light from those galaxies must be suffering a deterioration along the way, since none of them have a clearly galactic appearance.
 
The sensor issue is the key of course, and whereas we have the huge connected radio telescopes, they haven't put together anything nearly as big optically. I kinda thought (and here's where your photo expertise comes in) that they could 'network' an array of optical telescopes or mirrors and accomplish the same thing...
 
It's funny, I don't know why I thought one could just look through a telescope and see the kinds of things one sees in "Hubble telescope photographs". But the more I look into them, the more I realize that they are really more like "creations" than "photographs"...... not that there's anything wrong with that.

News Releases


this little two minute video is handy for those who are intimidated by scientific reading..... Resource Gallery
 
But the thing that kicked this off, and it's a photo-resolution question**, is how can we see a star in Andromeda that's 15 trillion times its size distant, while the best we can do with Moon-situated objects is 3.8 million times their size distant?

**I can only guess that the stars in Andromeda are not resolved into round or near-round little balls, at any size the sensors at the telescope can image that way. The ability to image individual stars must be based on imaging the light coming from a star 'system' like the Solar System, and distinguishing that light from those of the nearby star systems. But the articles didn't even hint at that.
 
As an astronomer and a photographer this is pretty cool. The milky way was originally thought to be a Galaxy, unlike Andromeda, more like a large cloud when they later discovered the milky way was a spiral galaxy just like Andromeda. Andromeda gives us insight into what our own galaxy looks like. Our solar system rotates around the galactic center in an outer arm of the milky way. When looking at the Sagitarious constellation, we are looking toward the galactic center. When looking at Perseus or Cygnus, we are looking toward the edge of the galaxy. In many ways, studying Andromeda is studying our own Galaxy.

Also, just for reference, it would take a 200 meter diameter objective telescope to see the Flag on the moon if the telescope was earth based. The James Webb (Hubble replacement) will have a 21foot diameter mirror.
 
dalethorn said:
Just pondering these perspectives - since a Sun-like star in Andromeda is ~600 billion times its diameter distant (too small to see with anything), how about a galaxy near the edge of the observable universe? We know that Andromeda is about 7 times wider in the night sky than the full moon, so that's a huge target for a time exposure. A galaxy at the edge of the visible universe would be about 5000 times farther away than Andromeda, or about 125000 times its diameter (100k LY) distant. On the Moon we can resolve an object that's 3.8 million times its diameter distant. That should mean that the most distant galaxies, if they're the size of the Milky Way or Andromeda and in a favorable viewing angle, will be about 30 times bigger than the minimal viewing size. But given the actual astro-photos I've seen from the Deep Field series, the light from those galaxies must be suffering a deterioration along the way, since none of them have a clearly galactic appearance.
Click to expand...

I think there is also something to do with light emission and light reflectance in terms of resolution. For example, I can see a red light blinking on a tower miles away. But during the day, I can't see the light. The moon reflects light from the sun, while a star emits light and is a "point light source". Many features on the moon, like planets, are low contrast. Yet splitting double stars in a telescope of the same resolution in terms of arc seconds is easy, because these are two high contrast objects.
 
Just some more background:Point source - Wikipedia

While stars in the Andromeda are getting resolved, its the light coming from the stars thats resolved and the distance relative to stars around it. We are close enough to the sun we can actually resolve features that belong to the sun. All we are resolving are point sources in the picture of Andromeda, even though its distance to size is much greater than that of objects on the moon.
 
Luke said:
Jason, are you kind of saying that we are seeing light from the stars...... not the actual star itself?
Click to expand...

Well, the 328 feet long object resolution limit from the Moon is easy enough to calculate as 3.8 million to one. The telescope guys also talk about 0.04 arc seconds or something similar as a limit. But I haven't seen the resolution-enhancing software factored in, where it removes atmospheric effects - I assume it's already factored in. So the 3.28 million to one resolution of Moon objects translates to us seeing the body of a Sun-sized star only out to 1/2 of one light year. That's a long way from 2.5 million light years, or a 5 million times under-limit of resolution size at Andromeda. I understand the point-source phenomena, but can it hold up for 5 million times less linear size? Could that be because of long time exposures that we can see point sources (stars) that small? Then you'd need something to prevent over-exposure toward the galactic center.
 
Luke said:
Jason, are you kind of saying that we are seeing light from the stars...... not the actual star itself?
Click to expand...

Sorta kinda yeah. LOL. For example, one way they've been able to discover dark matter and black holes is because they can detect the light from a star bending before it gets to earth.
 
Djarum said:
Just some more background:Point source - Wikipedia

While stars in the Andromeda are getting resolved, its the light coming from the stars thats resolved and the distance relative to stars around it. We are close enough to the sun we can actually resolve features that belong to the sun. All we are resolving are point sources in the picture of Andromeda, even though its distance to size is much greater than that of objects on the moon.
Click to expand...

When I was doing B&W prints from a cheap enlarger, I ran across the concept of point source (or something similar) lighting compared to diffuse lighting from the enlarger bulb. As best I remember, the "point source" provided greater detail, but could make grain objectionable in some photos.
 
dalethorn said:
Well, the 328 feet long object resolution limit from the Moon is easy enough to calculate as 3.8 million to one. The telescope guys also talk about 0.04 arc seconds or something similar as a limit. But I haven't seen the resolution-enhancing software factored in, where it removes atmospheric effects - I assume it's already factored in. So the 3.28 million to one resolution of Moon objects translates to us seeing the body of a Sun-sized star only out to 1/2 of one light year. That's a long way from 2.5 million light years, or a 5 million times under-limit of resolution size at Andromeda. I understand the point-source phenomena, but can it hold up for 5 million times less linear size? Could that be because of long time exposures that we can see point sources (stars) that small? Then you'd need something to prevent over-exposure toward the galactic center.
Click to expand...

The problem with dealing with stars is that they are point sources and the distance to "size" rule falls apart. What I mean is this. Star A and Star B could be the same exact diameter. They could appear to have the same exact brightness (same diameter, different amounts of light output). One could exist twice as far away. But they both take exactly one pixel on a CCD. So deciding the "diameter" of the star doesn't work based on how many pixels it is, or converting pixels to arc-seconds. The other obvious problem with point sources is that the longer exposed onto a chip is that the other pixels could "bloom" indicating the star is larger when in fact it really isn't. Also, the longer exposure detects a star farther away while a closer brighter star still only takes up one pixel on a CCD.

http://starizona.com/acb/basics/observing_theory.aspx

At the end of the page:
"Certain objects, such as close double stars or thin linear features, may be visible below the threshold of both the telescope optics and the observer's eye, due to the effects of diffraction, the stimulation of larger numbers of cones, reduction of pupil size when viewing bright objects, and contrast effects. From personal experience, using a high quality telescope, the author has seen a 0.6-arcsecond double star clearly defined in a 6" telescope, which has a theoretical resolution of only 0.9 arcseconds. As contrast lowers, the resolution of the eye decreases, so planetary detail may not be as finely resolved as stellar or lunar details. The same is true of deep-sky objects"


Dawes limit states that the hubble can only resolve at .049 arc seconds. So, no atmospheric turbulence to worry about, no adaptive software required. What this really means is that we can't resolve stars that are closer than .05 arc seconds to another star.

Resolving power takes wavelength of light into account, and this is why X-Ray telescopes are important, because they can resolve more with less diameter.
 

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