Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 07/01/2010 04:11:37
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What is the heliopause (presumably not the pedological equivalent of a menopause), and why is it important?
Chris
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I'll quote directly from from wikipedia as it's as concise an explanation as any:
The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars.
There's also considered to be a heliopause between the Earth and the Sun due to Earth's magnetosphere blocking and diverting the solar wind.
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The distance to the solar system heliopause must be enormous though, presumably?
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Hmm... although that wikipedia article I linked to says that it's the point where the local stellar wind is balanced by the combined stellar winds of the surrounding stars, which implies that the heliopause is located roughly half way between stars (depending on the type of star), it is more due to it no longer being strong enough to compress the rarified hydrogen forming the interstellar medium, along with the the virtual particles popping into and out of existence in interstellar space, which finally halts it.
As such, the solar wind is halted well before it actually encounters the stellar winds from nearby stars, and so is not roughly half way between them but much closer to the local star.
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We did all about this in our Solar-Terrestrial physics lectures ... but that was well over a decade ago and I don't remember the details.
I don't have it to hand, but am pretty certain the answer will be well-explained in this textbook that we used:
http://www.amazon.co.uk/Introduction-Physics-Cambridge-Atmospheric-Science/dp/0521457149/ref=sr_1_20?ie=UTF8&s=books&qid=1263033148&sr=1-20
I'm sure you can browse for the answer in a local Cambridge bookshop.
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Big rivers maintain their coherence quite a long way into the oceans.