Stellar Oscillations across Spiral Arms

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19 years 4 months ago #13374 by Jim
Replied by Jim on topic Reply from
LB, How do you know how fast the average interstellar speed of particles is 25,000m/s? Is that a given in the models you are using or is there data indicating it is 25,000m/s? Are you saying any comets in interstellar space are moving that fast? Or is it the space between the stars is empty?

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19 years 4 months ago #13375 by Jim
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I examined as best I could your statement about what I meant about bodies accelerating in a gravity field. My statement is better and clearer to me because you are using the sun rather than the excape velocity as the focus.

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19 years 4 months ago #13550 by tvanflandern
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Larry Burford</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[Jim]: If stuff was flying around at an average speed of 25,000m/s relative to the sun there would be a huge number of crashes with all the solar masses.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">[Larry]: Wow. You have a very strange mental image of how close things are to each other out there.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">To illustrate Larry's point, which is correct, I often quote this "wow" statistic about the Oort cloud, which is closer to us than any other star:

The volume inside the orbit of Pluto is large enough to contain all 200 billion stars in the Milky Way galaxy without touching. The volume inside the Oort cloud is large enough to contain all the stars in the roughly 10 billion galaxies in the visible universe without touching. -|Tom|-

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19 years 4 months ago #13421 by Jim
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Wow that is a lot of volume. So, does that mean anything flying around in the interstellar volume has an average speed of 25,000m/s relative to the sun?

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19 years 4 months ago #13383 by PhilJ
Replied by PhilJ on topic Reply from Philip Janes
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Jim, June 27: So, a comet if it comes from some place outside the solar system it is coming into the gravity system of the Sun at a speed above the excape velocity of the sun's gravity and will slow down relative to the excape velocity as it nears the Sun. <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Less confusion would result if you say what you mean: i.e.: A fast incoming comet loses <u>energy</u>, while a slower one gains energy. Obviously, either one will gain speed until it reaches perihelion and lose speed until it reaches aphelion.

It is true that most comets are negligibly influenced by the planets, and their trajectories are therefore 2-body problems. Capture requires planetary influence.

I don't claim to be an authority on this subject, but as I understand it: The "slighshot" effect only boosts a comets energy if the comet passes close to a planet on the planet's right side (with north up). If it passes on the left, the comet will lose energy. In either case, the comet's new perihelion may be below the Sun's surface. A subsequent planetary encounter is then needed to prevent collision with the Sun.

The same is true if a comet or asteroid passes the Earth-moon system: Depending on size and incoming velocity, it could be slowed by passage thru the upper atmosphere to a collision trajectory, and on passing the right side of the moon, it could be slingshotted into a more stable orbit. Subsequent passes by the moon would tend to circularize its orbit.

Schumacher-Levy 9, 1993, is a made-to-order example of cometary capture. The commet's initial energy loss was due to extreme tidal forces tearing it apart, though Jupiter's moons may have also played a role. While most of the comet impacted on Jupiter, it apparently left a [url] www.atsnn.com/story/36924.html [/url] new ring of cometary fragments. Had the initial encounter been very slightly different, Jupiter might have acquired several additional moons.

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19 years 4 months ago #13476 by Jim
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PhilJ, The energy of both comets will increase because of speed-would it not? The point is comets can be captured from interstellar space so there is no need for storage in the Orrt Cloud. In fact there is no need for that model at all as far as I can tell. And if comets do in fact come from interstellar space the whole topic needs a rethink.

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