1) Is our galaxy (Milky Way) a downward spiral or flat disc?

2) I mean, are the arms like the blades of a fan, or is it like a whirlpool / abyss, with things constantly getting sucked into some nothingness, slowly but inevitably?

2a) Any idea about the dimensions, and the proportion of our solar system to the size of the spiral arm as well as the galaxy as a whole?

2b) Are all spiral arms of equal size and symmetrical?

3) If it's like a fan blade system, then we must be constantly rotating / revolving, without our solar system really moving itself. Or, does the solar system simultaneously travel within the spiral arm?

4) On a fan blade, the dust particles don't move. The matter that makes up the blade also does not move in itself. But the blade as a whole moves, and the dust particles that are superimposed on the surface of the blade thus move. Is our solar system superimposed as a layer on the surface of one of the spiral arms of Milky Way?

Your conception of the galaxy needs some adjustment. I would sagest you have a look at the images available of the Andromeda Galaxy. It is a lot like our Milky Way. Rather than a fan blade system, I would rather this; A very large decathlon wheel. The star groupings and other mater orbiting stars is all moving around the wheel. The galaxy is rotating. The spiral arms are not all even. They appear to be more dense nearer the central bulge of our galaxy. The outer regions of the arms are much more defuse. The central area is moving much quicker than the outer area. Make a coffee, stir it. Watch that little bit of fluff in the center (the froth) Imagine thats the whole life of a galaxy, Spinning, moving, and constantly changing. As for our solar system. I would not sagest much change from our movement in my life span., but it is changing constantly. It moves up and back through the spiral arm we are part of. Go do a search of galaxy images, . You ask about size of the solar system and galaxy. Thats not so easy to image in your mind. Think big. We use the term 'light year' to help us understand the huge distances involved in this subject. The following is not an absolute, but should help you understand all this. . . We are very near our sun in astronomical terms. The light from the sun reaches us in just 8.5 Min's. That distance is 150,000,000 ( thats 150million kilometers) So we use light speed as a smaller number. 8.5 is easy'er to follow. This whole solar system is only about 10 hours across. This is still a small number. I am confident others will state more accurately this size aspect.

if the galaxy were reduced to 130 km (80 mi) in diameter, the solar system would be a mere 2 mm (0.08 in) in width.


more info on structure, shape and age of miky way http://en.wikipedia.org/wiki/Milky_way

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Thanks much. Wikipedia was interesting. Truly mind-boggling and difficult to: imagine in mind, to conceptualize to understand.