In message , Ted Sung
writes
Could someone explain why a precise measurement of an AU is important?
I faintly remember reading something about how Shapiro's radar
reflecting expermiments (in the 60s/70s) increased the precision of
this measurement dramatically but forgot why it had an impact
(presumably it was needed to precisely calculate orbits so that we
could sent the various explorers to other planets.).

Thanks,

Ted

[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%.
--
Save the Hubble Space Telescope!
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