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Re: RE: Re: LightYear Conversion is Incorrect in Units Package


LightYear is an easy to understand unit. But scientists (astronomers) don't 
use it in calculations (parsec, meter are used).


On Thursday 03 May 2001 10:28, David Park wrote:
> All the figures I give here are the same in the NIST Guide to SI Units
> which Urijah gives a link to, and the CRC Handbook of Chemistry and Physics
> 75th Edition.
>
> The conversion for LightYear is 9.46073*^15 Meter.
> (Mathematica uses 9.4605*^15 Meter)
>
> The conversion for TropicalYear is 3.155693*^7 Second (== 365.2422454 Day)
> The conversion for SiderealYear is 3.155815*^7 Second (== 365.2563657 Day,
> close to Mathematica)
> (Mathematica has 365.24219 Day for the TropicalYear)
>
> I changed the Units package by putting in the better value for LightYear.
> Then if I convert 1 LightYear to Seconds (using c = 1) I obtain
> LightYear -> 3.15575984236401*^7 Second
>
> This is just in between the TropicalYear and SideralYear. The NIST notes on
> light year say: "This conversion is based on the astronomical unit of time
> of one day (86400 seconds); an interval of 36525 days is one Julian
> century." They don't tell us how many days are taken in a year. Why light
> year is not linked to some common definition of Year is beyond me.
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
> > From: Urijah Kaplan [mailto:uak at sas.upenn.edu]
To: mathgroup at smc.vnet.net
>
> To: mathgroup at smc.vnet.net
>
> > The plot thickens...it seems that Mathematica uses a year of
> > 365.24219 days
> > or so, but the National Institute of Science and Technology says (see
> > http://physics.nist.gov/Pubs/SP811/contents.html page 64 of the pdf or
> > you can find it at http://physics.nist.gov/Pubs/SP811/appenB8.html )
> > mandates that for this purpose, a year is 365.25 days, which makes a
> > light year 9.4607*^15*Meter, which is different from what Mathematica
> > says. So it is a
> > bug!


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