Re: Sun's distance (2)

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

> How was the earth's distance from the sun determined using the transit of
> Mercury?

I don't think I can answer this question (in fact I know I can't),
but I think that the most precise determination of the size of the
astronomical unit (A.U.) prior to the development of radar involved
the determination of the distance between the earth and the asteroid
Ceres in the late 30s when Ceres was particularly close to the earth,
close enough that its distance could be determined accurately by
triangulation. Given that distance it is a relatively straightforward
application of Kepler's third law to determine the A.U., knowing the
orbital periods of both Ceres and the Earth, and therefore their
respective distances from the sun in A.U.

Of course the actual calculation took several years (interrupted by
WWII) in order to make the precision of the result as high as
possible I don't think the final result was announced until the early
50s.

Hugh


Hugh Haskell
<mailto://hhaskell@mindspring.com>

Let's face it. People use a Mac because they want to, Windows because they
have to..
******************************************************