A still more glorious dawn awaits - or does it?

January 12, 2015 10:31 AM

Tricky query to formulate so bear with me... I'm curious to what extent that astrophotography images represent the form of their subject matter, and whether the chorus to this song could ever actually happen. More inside....

I'm often curious with images like this, and other astronomy photographs like it. Since the distance to the subject matter is immense, extreeeeeme foreshortening must occur. The subject of the image that we're seeing most likely does not exist in the 'form' presented, but rather spread out over vast distances and tracts of empty space. Positions and relative sizes must be hugely distorted by the distances involved. The pillars of creation image, for example probably doesn't exist as three pillars (though i'm happy to be corrected) as shown, but could be practically any shape so long as it results in the image above when foreshortened.
Question is: is there any other viewpoint in the universe that would give the same image to the unaided eye?

For a simpler example have a look at this stunning video. Now this is not what this scene would have looked like to the revellers captured. This effect only exists because the photographer was over 2km away. If you travelled in a straight line towards the moon in this video until you got to the people, you wouldn't ever get to a spot where this viewpoint exists to the naked eye.

For some reason this is both awe-inspiring and slightly disappointing. I can't put my finger on why.

For an even more boiled down query:

"A still more glorious dawn awaits
not a sunrise, but a galaxy rise
the morning filled with 400 million suns
the rising of the milky way"

Could this actually happen? Could it happen to the extent that the galaxy occupies a similar size in the sky as the sun does? And would it look like the spiral-armed galaxies that astro images show us?

posted by 5imon to Science & Nature (5 answers total)

I'm not quite sure I fully understand your question, perhaps others do.

For your last question, though: Under dark skies the Andromeda galaxy, the most distant object visible with the naked eye, appears as a faint smudge even larger than the sun. The Milky Way, our home galaxy, takes up half the sky under dark skies. However...

Most astrophotographs taken of things beyond our solar system are long-exposure photographs or, more likely, a composite of several (even thousands) of long-exposure photographs.

So when you look at the Andromeda galaxy with your naked eye, or even through binoculars or a telescope, you see a faint smudge with a bright center. When you can see the glow of the Milky Way Galaxy, you see a "milky" glow across the sky with various lighter and darker spots. If you take a long-exposure photograph of either you will see much more of the structure.

Other galaxies, ones that take the classic spiral shape, are even smaller and fainter through a telescope. Open your camera's shutter for a minute or so and you'll see the classic spiral arms.This is true of most deep-sky objects. With just a couple exceptions, nebula never show any color when you look at them. Only through a long-exposure photograph do they start to show color. In fact, a lot of nebula only show color when the infared is exposed.

I've simplified it a bit, of course. Modern astrophotographs are also usually processed with Photoshop or, more commonly, specialized astrophotography tools. No information is added but these tools are used to enhance the information that has been exposed.

There's also the fact that the Earth rotates so to take a proper long-exposure photograph of more than a second or two requires the camera to be mounted on a motorized platform that will rotate the camera along with the stars.

For your Moon example, the Moon is enlarged via the use of a telephoto lens. The people in that photograph would have seen the Moon rise, but it of course would not have looked as large. One certainly can see the Moon rise, however, and I urge you to check it out some time. Most of us have seen sunsets and sunrises but seeing the Moon rise, especially behind some mountains or pine trees, is a truly special thing.

I cannot speak to the Pillars of Creation photo because if I attempt to think about it my brain explodes and I don't want to mess up my cubicle walls.

So, in short, most astrophotgraphs of deep sky objects take in a lot more light than can be seen with the naked eye, and are processed somewhat after the fact. While they represent their subject, they do not represent how you can see that subject.

Plenty of astrophotographs, primarily of the Moon and other Solar System objects, are short exposure and pretty much represent how the subject would look if you were close enough to see it the way your camera or telescope does.
posted by bondcliff at 11:01 AM on January 12, 2015 [1 favorite]

You can see a galaxy-rise if you want. The andromeda galaxy is large in the sky, but faint. Here a nice example. You can see a lot more detail with just a pair of binoculars. Just imagine someone looking back at you in a dim and fuzzy milky way from their own night sky somewhere in andromeda.
posted by Poldo at 11:22 AM on January 12, 2015 [1 favorite]

I don't know if you've ever been in a place dark enough to really see the Milky Way, but we're inside a huge galaxy, and it is flat out amazing. Something like this is at the limit of human perception, but in a dark enough clear place and enough time for your eyes to adapt you really can see those dark cloud-ish structures, and even with the camera those are sub-minute exposures.
posted by straw at 12:23 PM on January 12, 2015

Here's a comparison of Andromeda and the full moon in the sky. It's a literal galaxy rise filled with "400 million suns" - here's the zoomable version of the 1.5 gigapixel image released by the The Panchromatic Hubble Andromeda Treasury at the same meeting as your Eagle Nebula revisited image. (Really, just try the zoom out in full screen mode. It's incredible.)

In general, you're right that distant, large, and diffuse structures will not look like their images if we get close enough to see them with the naked eye. But that doesn't make them any less real, though... (At the end of that line of reasoning, you end up with "brain in a vat" - is anything real?)
posted by RedOrGreen at 12:29 PM on January 12, 2015

In the Pillars of Creation picture you linked, the most serious foreshortening effect would be for the stars: some of them are probably much nearer to us than the nebula, others are definitely much further away. But the nebula itself is all basically one object so its thickness/depth from our viewing point wouldn't be much more than its apparent width. You can take heart that it's all one big blobby thing.

There are tricks that astronomers can use to measure and/or guess the three-dimensional shape of nebulae. I don't know much about them but I think one technique uses the fact that the dustier parts are only reflecting the light of nearby stars, and cast shadows. This is a really amazing animation of an educated guess about the shape ("form") of a nebula and its nearby stars. Seriously check it out, it's awesome.
posted by traveler_ at 12:46 PM on January 12, 2015 [3 favorites]