In article ,
Jonathan Silverlight wrote:
(quoting a moderator's note)
[Mod. note: because it determines the baseline for parallax
measurements, an accurate value for the AU is also vital to accurate
measurements of distances outside our solar system -- mjh]

But isn't the error in measurements outside the solar system almost
entirely due to errors in the small angles involved? For instance we
know the distance to Deneb to within 36%, but the distance to alpha
Centuari to 0.23%.

Different sort of error. Not knowing the AU precisely gives you a
systematic error -- at least if you want to convert distances into
metres and do physics with them. Not being able to measure parallaxes
precisely gives you a measurement error, which is what you're talking
about.

Martin
--
Martin Hardcastle Department of Physics, University of Bristol