Posted on 07/03/2008 6:20:41 AM PDT by Abathar
No.
There is no wind in a vacuum.
There is no sound in a vacuum.
Therefore the term “supersonic” is dead wrong.
The solar wind isn't a vacuum. The article is about the behavior of a stream of particles; the presence of those particles themselves makes it, by definition, not a vacuum.
The terms known as "vacuum" and "zero-gravity" are good enough for the vast majority of uses, but "near-vacuum" and "microgravity" are more strictly correct.
The behavior described is the same as that of air particles in the Earth's atmosphere. The particles at that speed can't get out of each other's way, forming the shock wave that's known as a sonic boom. Can the resulting vibrations be called "sound"? That's a semantic question. The solar wind is like a tree falling in the woods with no one to hear it.
Insofar as there is really no perfect vacuum in nature (even in deep space hydrogen particles exist even if far apart) I still say that the use of the term supersonic is ridiculous.
The solar wind is nothing like atmospheric wind. There is nothing even remotely approaching the density, and even the term supersonic would vary with density as the speed of sound does.
The speed in units is irrelevant; what's at issue is where the shockwave phenomenon occurs. The equivalence between "supersonic" and 340.3m/sec. is only valid at room temperature and sea level, but it's close enough that airplane and spacecraft speeds are expressed in Mach units.
I agree that more precise terms exist, but "supersonic" is not flat-out wrong -- just vague to a degree that I would not consider acceptable in a scientific journal, but which is good enough for an article directed at a general audience.
You’re splitting hairs, needlessly. You know they’re using “the speed of sound” to represent the accepted constant of 1088 feet per second used in mach units.
check out
spacesounds.com
1) I am not splitting hairs needlessly. It is an asinine term to use and does nothing but confuse people, especially any kids who might be reading it. Hollywood already does a wonderful job of ignoring the vacuum of space.
2) I let it go almost a full day ago.
Michelson-Morley, anyone?
Funny thing is that I read they actually did find a difference, but it was deemed by the “establishment” at that time to not be enough to be statistically significant.
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