RE: Re: LightYear Conversion is Incorrect in Units Package

*To*: mathgroup at smc.vnet.net*Subject*: [mg28635] RE: [mg28627] Re: LightYear Conversion is Incorrect in Units Package*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 3 May 2001 04:28:25 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

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 > > 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! >

**Follow-Ups**:**Re: RE: Re: LightYear Conversion is Incorrect in Units Package***From:*Jean-Marie THOMAS <jmt@agat.net>