On Saturday 02 April 2011 20:36:43 Paul Rittman wrote: > So would you folks advise (1) being purist, and quoting > inter-stellar distances as “ultra-giga-multi-meters” or whatever; (2) in > parsecs, which is almost entirely unknown to civilians; or (3) stick with > the term “light-year”? And just as importantly, why?
Prefixes are used with the meter, of course, and also with the parsec. I'm not sure if they're used with the light-year. Of those units, direct measurements are possible only in parsecs (by waiting six months and seeing how many arcseconds the star appears to move). I've heard of astronomers measuring in milliarcseconds, so kiloparsecs should be doable this way, but not megaparsecs. Red-shift measurements have to be converted, whatever units they are converted to. I think the general public would need an explanation of whatever units are used. I suggest giving a few distances in all three units, in case the audience is not all familiar with the same unit, and then using petameters, exameters, etc. for the rest. The public may not be familiar with those big prefixes either. A number you may find useful is 206264.8. It's the number of arcseconds (approximately) in a radian; multiply an astronomical unit by that and you get a parsec. I use the number occasionally in surveying. The mantissa of its reciprocal is 4848137; I use the three 48s to check whether I remember the number correctly. Pierre -- When a barnacle settles down, its brain disintegrates. Já não percebe nada, já não percebe nada.
