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What does the universe look like?

I watch these magnificent programs about the universe, so wonderfully explained by Morgan Freeman.  I am puzzled with one question.  How can the science predict the size of our galaxy in somewhat vivid details? 

So, here is my analogy.  With the space technology at hand, taking a picture of our own galaxy is the same as taking a picture of the Empire State building from one of its balconies. 

Can someone please elaborate on this subject.

Thank you.

Kiteman1 year ago
They don't predict it, they measured it. Once you know the relative positions of the various stars, it can be modelled from any point of view, be it fromwithin the Milky Way or from beyond its bounds.

Your analogy is faulty, because there are no gaps between the girders and concrete of the Empire State, through which we can see all the parts beyond. The gaps between the parts of our galaxy a hundreds of trillions of times larger than the stars themselves - to make your analogy accurate, you would have to replace each girder, block and slab of the building with a single atom, which would render the whole building utterly transparent.

kabira (author)  Kiteman1 year ago
Hello Kiteman,

Thanks for the reply.

Ok, I get what you are saying that it is based upon modeling using the measurements we have taken over a long period. However, while we are rotating and taking all these measurements, rest of the objects in the universe are also on the move. The computer models can accurately create a model of the shapes only if we know the way other planets/galaxies are moving. In other words, how do we accurately know how and what speed they are moving?

Kiteman kabira1 year ago
We know which way they are moving because we can measure their speed - their red-shift gives us the speed away from us, and parallax gives us their speed perpendicular to the line-of-sight. Combine these, and we can say which way they are going, and how fast.

Plus, compared to the scale of the universe as a whole, they are moving very slowly. Although all the stars we can see are moving, many of them at different speeds and in different directions, when we look at the sky, we see basically the same arrangement as the first astronomers did.
One of the nice things about knowing Einstein's theory of special and general relativity, is that your measurments can be made accurate as you take into account our movement, the expanding universe's movement, and etc. A LOT of laws and such come into play in this (from the Doppler effect, all the way through Kepler, Kirchhoff, etc. etc. without a basic grasp of physics, trying to understand the wonders of astrophysics or theoretical physics is like giving the Encyclopedia to someone that just learned to read "Clifford, the big red dog".
No offense intended; but it really is hard to construct something if you don't recognize the parts and how they work.
Take a look at Google's 100,000 star project.
Have a look at this TED talk. It touches on the subject of the shape of the universe.
kelseymh1 year ago
Kiteman did a good job, and there is more. Materials are opaque, or transparent, to radiation at many different frequencies. Dust which is opaque to visible light is completely transparent to radio and microwaves. Hydrogen gas, like most of interstellar space, is transparent to visible light, but opaque to radio waves around 21-cm wavelengths. So astronomers use telescopes sensitive to all kinds of different radiation, from radio all the way to gamma rays, to see the Universe around us.
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