Re: [GZG] AUs, Gravity wells and FTL

David wrote on 08/07/2005 12:31:49 AM:

> A dumb question - I recall that an AU, or Astronomical Unit, is the 
radius
> of Earth orbit, eg approx 93 million miles.  Is this AU still approx
93
> million miles if used as a measure in another stellar system?  I can't
> recall if the measure of an AU was in some way connected to our own 
solar
> system, or if it was just a convenient way of handling large,
> sub-interstellar, distances?

Point of view thingie: if it's an exploratory mission from Terra, AU's 
will be approx 93 million miles, average radius, I gather. If it's
'home', 
whether indigenous or Earth 'lost colony' that's had to go through a 
rebirth of civ, they'll probably have their own local definition.

> The Earth's orbit doesn't *have* a radius, because it's not a circle.

True, but as one focus is the 'point of view', average radius would
work, 
and does in common usage. Without getting into arithmetic or geometric
or 
harmonic mean. ;->=

As a further complication, I've seen semimajor axis as the definition,
but 
I gather that it's closer to the mean of the semimajor and semiminor, 
right? Calculus required, which has been TOO many years, to get closer.

The_Beast
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