RE: Re: LightYear Conversion is Incorrect in Units Package

*To*: mathgroup at smc.vnet.net*Subject*: [mg28637] RE: [mg28627] Re: LightYear Conversion is Incorrect in Units Package*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 3 May 2001 04:28:27 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Investigating some more, it appears that the LightYear is the distance that light travels in 365.25 days (what might be called a JulianYear?). Since the speed of light is defined exactly, and the number of seconds in a Julian year is also exact, there is no reason why the conversion from LightYear to Meter can't be exact. Needs["Miscellaneous`PhysicalConstants`"] (365 + 1/4)(60 60 24)Second %SpeedOfLight 31557600 Second 9460730472580800 Meter For those who care about such things, the above conversion factor could be substituted in the Unit package for 9.4605*^15 Meter (Mathematica) or 9.46073*^15 Meter (NIST and Handbook figure). Also 1 LightYear is equivalent to 1461/1460 Year. 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! >