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 > 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!

**References**:**RE: Re: LightYear Conversion is Incorrect in Units Package***From:*"David Park" <djmp@earthlink.net>