Re: [office-formula] light years, Astronomical Units, and Parsecs

[Patrick Durusau <patrick@durusau.net>]

Dennis,

It has "....has to be correct, it has to be exact..." because it is an 
scientific fact, but not perfectly exact.

http://www.acme.com/jef/singing_science/scientific_fact-32.mp3

;-)

I think we need to put this in as a reference.

Hope everyone is looking forward to a great weekend!

Patrick

On 4/9/2010 12:35 PM, Dennis E. Hamilton wrote:
> This is getting ridiculous.
>
>    1. Note that 9.460530 is a 7-digit value.  Yet it is scaled to 10^17
> centimeters.  I have no idea if this is the best approximation to which the
> value of the light year is known, but it is clearly an approximation stated
> to a ridiculous scale.  9.460530 X 10^12 km is better.  So a light year is
> around 10^13 km and the value given suggests that it is known to within
> about 10^6 km.  (For comparison, the diameter of the Earth is on the order
> of 10^4 km.  There is no exact diameter of the Earth, but 1.274 X 10^4 km is
> a middling value.  These days, the diameter varies over a range of 40km or
> so. )
>
>    2. This demonstrates that we should not use "exact" for this kind of thing
> and we should probably not use "exact" where we do use exact, because often
> the conversion factor is itself not assured to be exactly-representable.
> Where the conversion is set in a standard, that is a different matter but we
> should probably say that is the source of "exactness" de jure.  That still
> leaves the problem of the fundamental units, the standards for which are
> ultimately dependent on a physical artifact or apparatus that sets the unit.
> Then there's the (different) problem of the accuracy of the data being
> converted as well as the specified, even de jure, conversion factors.
>
>    3. It might be better to find the best currently-available value for the
> speed of light, in m/sec., and state that to the appropriate precision as
> the nominal value somewhere.  (If we were to know the assumed error of
> measurement, all the better.)  Implementers and users can figure out the
> rest, given the definitions that don't require independent measurement (we
> know how many nominal seconds are in the nominal 365.25 days).
>
> I suppose this merits a JIRA issue too, although I am not sure how to state
> it.
>
>   - Dennis
>
> -----Original Message-----
> From: Patrick Durusau [mailto:patrick@durusau.net]
> Sent: Friday, April 09, 2010 07:48
> To: office-formula@lists.oasis-open.org
> Subject: Re: [office-formula] Straw poll - slug (and lightyear)
>
> [ ... ]
>
>
> Conversion factor? Ok, I had to get up out of my chair but:
>
> light year ly = 9.460530 X 10^17 cm
>
> Source: Kenneth R. Lang, Astrophysical Data, Springer-Verlag, 1992.
>
> Would it be better to state it in centimeters?
>
> Hope you are looking forward to a great weekend!
>
> Patrick
>
> PS: I can also insert more exact measurements for Astronomical Unit, Parsec
> and Megaparsec if anyone is interested.
>
>
>
>
>
>
> 	  Eike
> 	
> 	
>
>
>    

-- 
Patrick Durusau
patrick@durusau.net
Chair, V1 - US TAG to JTC 1/SC 34
Convener, JTC 1/SC 34/WG 3 (Topic Maps)
Editor, OpenDocument Format TC (OASIS), Project Editor ISO/IEC 26300
Co-Editor, ISO/IEC 13250-1, 13250-5 (Topic Maps)