Re: [Celestia-developers] Conversion error
Real-time 3D visualization of space
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From: Fridger S. <fri...@de...> - 2005-03-26 16:47:34
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Christophe, since there is this intrinsic conversion ambiguity, the unit ly [km] is=20 called a /depreciated/ unit in our LBL ParticleData base,=20 http://www-theory.lbl.gov/. Using the Julian year is of course also=20 possible and leads to something like the average over the tropical and=20 sideral year values. It is mainly the question what definition Chris=20 implied in Celestia when he introduced that constant...As long as one=20 does not mix the definitions, everything should be allright ;-) . That's=20 why I wrote in my first email that /he/ should make his choice. In any=20 case the differences we are talking about are /much/ smaller than the=20 error that was previously introduced via the typo! Bye Fridger Christophe Teyssier wrote: >Isn't the reference for a light year the julian year rather than the tro= pical=20 >or sideral? > >In any case that's what Wikipedia and my units.dat file say. > >1 ly =3D 365.25 * 86,400 * 299,792,458 =3D 9,460,730,472,580,800 m > > > >Le Samedi 26 Mars 2005 00:29, Fridger Schrempp a =E9crit : > =20 >>Chris, >> >>just for comparison, here are my values that are extracted from our >>professional, global data base for particle & astroparticle physics: >>http://www-theory.lbl.gov/ >> >>They largely refer to the Astronomical Almanac. >> >>The speed of light is unanimously: 299 792 458 [km/sec] >>One has to contemplate, however, how many sec's the year has in Celesti= a: >> >>The year 2005.0 according to the above source has >> >>tropical: 31 556 925.2 sec (equinox to equinox) >>sideral : 31 558 149.8 sec (fixed star to fixed star) >> >>The product gives for the light year in [km] >> >>tropical: 9460528172630.0 km >>sideral : 9460895298470.0 km >> >>So make your choice, please... ;-) >> >>Bye Fridger >> >>Chris Laurel wrote: >> =20 >>>Fridger, >>> >>>If it's true that there's an error in the conversion, I'll change it. >>>Since there are some other changes that will break some cel: URLs in >>>1.4.0, this is the right time to make a correction. >>> >>>--Chris >>> >>> =20 >>>>just in case you overlooked the recent forum post (2 days ago!) by t= he >>>>user 'tlittle' in Celestia Bugs. I think he is right! Celestia's >>>>conversion of 1 light year into km is significantly incorrect and >>>>probably due to a simple typo (one 9 too many ;-)). I checked all my >>>>scientific resources. They agree with 'tlittle's value. [At first, it= is >>>>a little tricky, since there are various differing definitions of '1 >>>>year' in astronomy, and thus of the number of seconds /year.] >>>> >>>>The correct revision of this value may have quite some interesting >>>>implications for our precision predictions, like various 'mutual' eve= nts >>>>etc. >>>> >>>>I am going to look into it in more detail. >>>> >>>>Bye Fridger >>>> >>>> >>>> >>>> >>>> >>>>------------------------------------------------------- >>>>This SF.net email is sponsored by Microsoft Mobile & Embedded DevCon = 2005 >>>>Attend MEDC 2005 May 9-12 in Vegas. Learn more about the latest Windo= ws >>>>Embedded(r) & Windows Mobile(tm) platforms, applications & content. >>>>Register >>>>by 3/29 & save $300 >>>>http://ads.osdn.com/?ad_id=3D6883&alloc_id=3D15149&op=3Dclick >>>>_______________________________________________ >>>>Celestia-developers mailing list >>>>Cel...@li... >>>>https://lists.sourceforge.net/lists/listinfo/celestia-developers >>>> =20 >>------------------------------------------------------- >>SF email is sponsored by - The IT Product Guide >>Read honest & candid reviews on hundreds of IT Products from real users= . >>Discover which products truly live up to the hype. Start reading now. >>http://ads.osdn.com/?ad_id=3D6595&alloc_id=3D14396&op=3Dclick >>_______________________________________________ >>Celestia-developers mailing list >>Cel...@li... >>https://lists.sourceforge.net/lists/listinfo/celestia-developers >> >> >>------------------------------------------------------- >>SF email is sponsored by - The IT Product Guide >>Read honest & candid reviews on hundreds of IT Products from real users= . >>Discover which products truly live up to the hype. Start reading now. >>http://ads.osdn.com/?ad_id=3D6595&alloc_id=3D14396&op=3Dclick >>_______________________________________________ >>Celestia-developers mailing list >>Cel...@li... >>https://lists.sourceforge.net/lists/listinfo/celestia-developers >> =20 > > >------------------------------------------------------- >SF email is sponsored by - The IT Product Guide >Read honest & candid reviews on hundreds of IT Products from real users. >Discover which products truly live up to the hype. Start reading now. >http://ads.osdn.com/?ad_ide95&alloc_id=14396&op=3Dclick >_______________________________________________ >Celestia-developers mailing list >Cel...@li... >https://lists.sourceforge.net/lists/listinfo/celestia-developers > =20 |