Hi Pat, I would refine your comment to say "Nor are they pro-SI," since astronomy does have a somewhat cgs culture.
There are plenty of cases in astronomy where SI isn't very practical. For example, say I point to a star in the sky and say that it's mass is about 10 000 000 000 Yg. That number conveys little or no understanding, even to the technically literate. It's inconvenient to say and write. How many people know what a Yg is? Alternatively, I could point to the same star and say its mass is 5 solar masses. Now almost everyone will have some appreciation for what that means. Astronomy deals with some pretty extreme numbers, far beyond the largest SI prefix. Already, the prefixes outside of the pico - tera range are pretty obscure. The BIPM could create prefixes to cover the extreme range used in astronomy, but there would be so many prefixes that you couldn't expect people to reasonably master them. So it's not surprising that astronomers invent their own units to cover these scales. There is another family of cases in astronomy where SI is not practical. For example, you can measure the distance to sources at very large distances precisely in terms of what's called "red shift," but we don't yet know the conversion from red shift to meters to better than 10% accuracy. Since this loss of accuracy is usually not acceptable, one is stuck using red shift. That said, I believe that astronomers have a terrible record for not making an effort to adopt SI units where practical. For example, the coordinate system for the celestial sphere is a horrible mess! Unfortunately, I don't see that changing anything soon. John On Friday 02 April 2004 16:18, Pat Naughtin wrote: > on 28/3/04 1:53 PM, John Hynes at [EMAIL PROTECTED] wrote: > > And I doubt that very many astronomers are anti-metric!!!! > > Nor are they pro-metric. They spend their night using the 'real' tools of > astronomical jargon: light-years, parsecs, astronomical units, Babylonian > angles and Babylonian time; and their days spent translating (dumbing down) > their favored jargon measures into 'popular' measures such as 'The asteroid > has a volume of 18 Olympic swimming pools'.
