My comments below. On Wed, 10 Sep 2003 19:48:33 +0100 "Terry Simpson" wrote: > I think 'million km' beats AU. I am familiar with metres and see them all > around me but have no idea about AU.
Normally I'd agree, but in a report about Near Earth Objects I think it's appropriate to use a Earth-centric measurement unit that gives "ballpark" distance approximations. More precise measurements would be done in km of course. This is a technical report made by working scientists for working scientists, so they don't concern themselves with the fact that the public doesn't understand what an "AU" is. I'm sure you realize that if it WAS written for the public, they'd be using feet and miles no doubt! Sad but true! > Incidentally, 'million km' is not the only SI compliant way of expressing a > distance of that magnitude. However, people appear reluctant to apply the > prefixes beyond kilo to metres and grams. Does anybody have any idea why > that is? Yes, that's irked me terribly too. In astronomy they always use millions or billions of km (mostly without any regard to the difference between American billions and English billions, but that's another problem, isn't it?) I have never seen Mm or Gm distances, and I really think they should be used. [Then again, I'm only casually involved in space science, so maybe there are some groups out there I don't know about that use these prefixes regularly.] I think that large km distances are used to avoid decimalized measurements (eg saying "Mars was recently 55,758,006 km from Earth" is better than saying "... 55.758006 Gm from Earth"). This follows the same reasoning for using only mm and m as standard units for measurement in the trades. David Shatto Los Angeles
