David Fontaine wrote:
> 
> > The weight is expressed in Newtons but the mass in Kg :).
> > But you are right for light year this is only for distance,
> > 1 light year is the distance that the light do in 1 year.
> > This is roughly 3*10^8 (m/s)*(3600*24*365)(s)=3*10^8 * 31,536*10^6
> > =9.46*10^15 meters =9.46*10^12 Km.
> 
> My calculator gives it as 9,460,528,404,879.4 km
> (3*10^8 is a *very* rough measure (and a year is 365.24 days))
> How come people never use the word megameters or gigameters or terrameters?

Yep but a good physicist can (must sometime) do good approximation to go 
to the essence of the problem :)!

But since you like precision, here is 

Tropical year (equinox to equinox)           31556925.2 secondes
Sideral year (fixed star to fixed star)      31558149.8 secondes

speed of light                               299792458 m/s

So we have:  9,460,895,298,474,208.4 m (for Sideral year) :)

And the error compare to my first result is only about 9.46*10^(-3)%

The calculations are right but I am kidding :)

Fabian.

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