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

• To: mathgroup at smc.vnet.net
• Subject: [mg28643] Re: [mg28635] RE: [mg28627] Re: LightYear Conversion is Incorrect in Units Package
• From: Jean-Marie THOMAS <jmt at agat.net>
• Date: Fri, 4 May 2001 00:23:09 -0400 (EDT)
• References: <200105030828.EAA20511@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```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
>
> > 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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