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I understand telescopes were used to observe and capture images of other galaxies. But, by risking the question sounding pretty ordinary, may I know how did we take the pictures or photographs of our home, the milky way galaxy (the beautiful spiral that we all are familiar with as shown below), given that Voyager mission took 35 years to even reach the heliopause?

Artist's rendition of milky way galaxy

Source : Universe Today

I'm sure there has to be some technique the scientists use to do that. (They don't have galactic selfie cameras yet, do they?) Can someone throw some light on this topic?

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    $\begingroup$ This may be a better question for Astronomy SE, but as it concerns how those observations were done, specifically mentioning probe missions, I say it is weakly on topic here as well. $\endgroup$
    – SE - stop firing the good guys
    Mar 20, 2017 at 10:01
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    $\begingroup$ @skrowten_hermit it might be better if you include at least a link to one or two specific examples of the kinds of images you are talking about, or included an image within your question - with the link to the source. It's not necessary since in this case they clearly can't be real images, but in general it's good to include specific examples in questions where possible, within stackexchange questions. $\endgroup$
    – uhoh
    Mar 23, 2017 at 5:01
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    $\begingroup$ @uhoh, just included an image just as you suggested. $\endgroup$
    – skrowten_hermit
    Mar 23, 2017 at 6:08
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    $\begingroup$ "...or included an image within your question - with the link to the source." It's best to credit the source of an image whenever possible. I know some images seem to be literally all over the internet, but it's important here both because of IP license issues, and it sometimes helps people trying to answer the question to review the source. $\endgroup$
    – uhoh
    Mar 23, 2017 at 6:22
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    $\begingroup$ You can see that pics about space credits sun.org which credits Wikipedia (though no link) and shows Creative Commons Attribution-ShareAlike 4.0 International License. $\endgroup$
    – uhoh
    Mar 23, 2017 at 6:26

2 Answers 2

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This is a good question and on-topic as far as I'm concerned. As you correctly point out our furthest reaching spacecraft is only at the heliopause, which is no real distance astronomically, and certainly not far enough to get a glimpse of our galaxy from an angle and distance which would allow that self-portrait. The images of the milky way galaxy are all artistic renditions, they are educated guesses of what our galaxy would look like based on observations of other galaxies and our own. Concentrations of matter have been extensively mapped in our galaxy using visible light and spectrum outside the visible range like infrared, x-rays, and others. These concentrations of matter show the structure of our galaxy even though we cannot observe it from an angle.

The next logical question is how do we know they are right, and the answer is we don't, not with absolute certainty. The map of our galaxy is based on observations from a single point, and interpreted using an understanding of the physical laws of our universe as developed over hundreds (or thousands) of years by some of the finest minds in history. Yet for all of the effort and brainpower it is still within the realm of possibility that this understanding is wrong in which case our map may be wrong.

It's going to take a long time before anyone gets far enough away to check that work in any case.

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  • $\begingroup$ I have read about and seen artistic renditions for supernovas, blackholes etc (Some of them looking like taken right out of the pages of a fantasy comic book). So, they are all sort of guessworks? Since milky way is visible in the night sky, these artistic renditions should have used that as a reference and bits and pieces of whatever information available and create the image, right? $\endgroup$
    – skrowten_hermit
    Mar 20, 2017 at 9:24
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    $\begingroup$ I hate to use the word guesswork, a better way to put it would be the best science possible with only one point of reference. You are essentially correct though. $\endgroup$
    – GdD
    Mar 20, 2017 at 9:54
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    $\begingroup$ @skrowten_hermit: Some of images of Milky Way are much more than guesswork - no more a guesswork than a map is a guesswork. We know how a generic galaxy looks from above, and we know the precise layout of Milky Way, so we can generate a very accurate rendition of how it looks like. $\endgroup$
    – SF.
    Mar 20, 2017 at 11:49
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    $\begingroup$ Your point is entirely valid @SF. and I don't think we disagree on it. The map of our galaxy is based on observations made from a single point, interpreted as best as possible using our understanding of the physical laws of the universe. $\endgroup$
    – GdD
    Mar 20, 2017 at 12:13
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We can't take photos of our own galaxy that show the beautiful spiral. From astronomical observations (both from the ground and from satellites like Gaia) we do have lots of data on stars inside our galaxy, including their positions. So we can create a visualization that shows the known stars and their positions. Part of the Milky Way is obscured by dust clouds, so in those directions the visualization has to include some guesswork.

This map shows radio telescope observations of the Milky Way. Gray and red are observations. The mostly-black cone radiating upward from our position (at +, straight below the center of the image) is an obscured area.

Milky Way hydrogen map

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  • $\begingroup$ Though I was unaware of such a technique, I had a hunch that some mapping process might be involved. Radio telescopes work in the same way a Radar or Sonar works? $\endgroup$
    – skrowten_hermit
    Mar 20, 2017 at 15:57
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    $\begingroup$ A radio telescope is a passive system, radar and sonar are usually active (they send out a signal and listen for its reflection). In this case, the radio telescope listens for transmissions made by hydrogen atoms. See en.wikipedia.org/wiki/Radio_telescope $\endgroup$
    – Hobbes
    Mar 20, 2017 at 16:05

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