# Solar system motion relative to the Galaxy

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I had always assumed that the galaxy's "arms" were more-or-less stable structures. Thus, I assumed that the solar system would more-or-less "always" be located at a given spot in one of the arms, and would spin around galactic center along with the rest of the arm. Lately, I have heard several references to the idea that the solar system actually travels through the arms. I am confused as to why that would be the case. Cursory thinking suggests to me that the same gravitic circumstances that create the arms would be the deciding factor. But I am apparently wrong,

So, can anyone please explain a) whether the solar system does actually move through the arms, and b) why this is the case.

Thanks!

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By way of analogy, think of a busy, but not overcrowded, freeway. Suppose some car changes lanes where it shouldn't. Drivers of the immediately adjacent cars will have to brake hard to avoid a collision. Drivers of nearby cars will have to brake because of the actions of those adjacent cars. The traffic slows down in the vicinity of this near accident. These slowdowns can persist for a long time if the freeway is busy. Many other factors such as busy interchanges, curves in the road, and changes in the number of lanes also cause areas where traffic slows down.

The car density, the number of cars per unit freeway length, will be higher than average at these areas of congested traffic. In other words, congestion spots are density waves. Density waves caused by obstructions are stationary. Those caused by near-collisions can move, but at a different rate than the traffic. Regardless of whether these density waves are stationary or moving, the cars move through them.

Now think of the galaxy as a rather large freeway. The stars are cars moving on this big freeway. The spiral arms are congestion areas, or density waves. Google "density wave theory" to read more on this topic.

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Thank you very much! I think I get it, but before I go off with enough rope to hang myself, let me extend this wave density concept to a couple of other phenomena:

Does wave density have a role in the so-called "Pioneer Anomaly?"

Does wave density have a role in the formation of planets at the orbital distances (from the sun) they occupy within the solar system?

Finally, let me say that I have been wishing for a place to ask questions like this for years. I have tried lots of "Ask the scientist" sites and tried emailing a few scientists directly, and have never gotten answers. Google is wonderful if you know the term you want to look up -- which your answer provided for me. So, thank you, again! Y'all are much needed and appreciated.

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"Density wave," not "wave density."

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Are we in a spiral arm? Where are we located with respect to the nearest spiral arm? How long does it take us to pass thru a spiral arm? Will the distance to the nearest stars increase, and by how much, when we pass out of a spiral arm?

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An astronomer had a program on a science channel.

His claim on a rotating Galaxie always ( Turn Counter Clockwise ) Boy is he:eyebrow: dumb for a scientist and probably wrote a gazillion books.

My observation and common sense that I know as no nothing heaven idea is that depends from what flat side you are looking at a flat galaxie.

From one side it turns counter clockwise, but from the other side it turns ( Clockwise ) Man-O-Man where do these Dolts get thier ideas to brain wash the public ?.

Merged post follows:

Consecutive posts merged

No never, we are locked in that river of the arm. Just drifting along on gravity. No we will never bump or pass throught any arm. We are DOOMED:eyebrow:

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/me steals Tolmosoff's parentheses. YARRR

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That will cost you \$20 bucks Yarrrr:cool:

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