on 4/26/2002 5:05 PM, Duncan Bath at [EMAIL PROTECTED] wrote: > It seems to me that the metre ... is unsuitable for the > description of interstellar and universe-type measurements. > > So, let's not try to use SI where it has no real application.
There is no such situation where SI has no application. As far as stellar distances are concerned, we don't use metres for distance between cities either; we use kilometres. So also we don't need to use metres to measure the distances between stars; petametres (Pt) will do quite nicely. For even larger distances, there are exametres (Em), zettametres (Zm) and yottametres (Ym). Some distances: 40 Pm to nearest star from the Sun 220 Em to center of our galaxy 21 Zm to nearest other galaxy 100 Ym to edge of observable universe* Sometimes, to make comparison, it is useful to put all these in the same units, for example, using exametres: 0.040 Em to nearest star from the Sun 220 Em to center of our galaxy 21 000 Em to nearest other galaxy 100 000 000 Em to edge of observable universe* or using zettametres: 0.000 040 Zm to nearest star from the Sun 0.022 Zm to center of our galaxy 21 Zm to nearest other galaxy 100 000 Zm to edge of observable universe* One can't do any better than that with light-years or parsecs. *Edge of observable universe data from a 1997 reference book. Regards, Bill Hooper retired physics professor, Florida, USA -------------------------------------- "Simplification" begins with "SI" --------------------------------------
