Re: Fwd: Re: [office-formula] Straw poll - slug (and lightyear)

[robert_weir@us.ibm.com]

"David A. Wheeler" <dwheeler@dwheeler.com> wrote on 04/07/2010 04:09:19 
PM:
> 
> Rob said, regarding light-year:
> > That matches the International Astronomical Union's definition as 
well, 
> > only they say as distance light travels in a vacuum in 1 Julian Year, 
> > which is 365.25 days.
> 
> Ah!  Can you post the citation?  I think we should cite a source.
> 

http://www.iau.org/public/measuring/

It says:

"Alternatively the light-year (ly) is sometimes used in scientific papers 
as a distance unit, although its use is mostly confined to popular 
publications and similar media. The light-year is roughly equivalent to 
0.3 parsecs, and is equal to the distance traveled by light in one Julian 
year in a vacuum, according to the IAU. To think of it in easily 
accessible terms, the light-year is 9,460,730,472,580.8 km or 63,241 AU. 
While smaller than the parsec, it is still an incredibly large distance."

And they cite for the entire web page (which discusses other topics as 
well): Seidelmann, P. K. (Ed.), 1992, Explanatory supplement to the 
Astronomical Almanac, University Science Books 

So I can't be certain that Seidelmann has that specific definition. 

But let me try something with Twitter to see if this social networking 
thing has any value.  Maybe someone out there has a copy....

-Rob


> > On the other hand, the IAU says Pluto is not a planet, so I don't know 
if 
> > we can trust them anymore.
> 
> :-).  I've posted my own thoughts on that here:
> http://www.dwheeler.com/blog/2006/09/01/#planet-problems
> But I'm no astronomer, so I'm certainly not an authority on the topic.
> 
> Anyway, I think we should be as accurate as possible on the 
> conversion function.
> It's an easy function to get 'slightly wrong' without anyone 
> noticing for a while,
> and that would be bad.
> 
> --- David A. Wheeler