Hi John,
Thanks for the FTL thoughts and the gravity well figures - have filed
them in my useful info file:)
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?
Regards
David
> From: JBrewer@webtv.net (John Brewer)
<snip of lotsa good stuff you'll just have to go archive diving for:) >
> David Billinghurst wrote:
> Hi John,
It's a relatively arbatrary measurement (being related to Terra's orbit), but
it does not change depending on the system used. It's just a
convenient way of handling large sub-interstellar distances.
> Regards
> On Sun, Aug 07, 2005 at 05:31:49PM +1200, David Billinghurst wrote:
> A dumb question - I recall that an AU, or Astronomical Unit, is the
Yes - it's a Terra-centric measurement standard, just as much as the
metre or the second. A truly generic measurement system would probably be
based on the Planck length.
R
> A dumb question - I recall that an AU, or Astronomical Unit, is the
The Earth's orbit doesn't *have* a radius, because it's not a circle. The
Astronomical Unit is roughly the mean distance from the Earth to the Sun, and
it is an arbitrary unit relating purely to our local solar system. For more
detail, including the formal definition (which doesn't refer to the Earth's
orbit at all, go here:
http://en.wikipedia.org/wiki/Astronomical_unit
David wrote on 08/07/2005 12:31:49 AM:
> A dumb question - I recall that an AU, or Astronomical Unit, is the
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
> At 10:46 PM +1000 8/7/05, R. Bryett wrote:
The
> Astronomical Unit is roughly the mean distance from the Earth to the
For
> more detail, including the formal definition (which doesn't refer to
Still, I suspect that for the purposes of describing another system, AUs would
be useful. People will still probably have Solar Day as a reference point when
we move out there, even if they do tell time by local revolutions.