"David T. Lewis" <lewis at mail.msen.com> writes:
> I'd like to know how a Barycentric Reference System works

For me, the hard part to understand about TCB (barycentric coordinate
time) is "coordinate", not "barycentric". A _barycentric_ reference
system is just a change of coordinates from coordinates with their
origin on the earth to coordinates with their origin at the center of
mass of the solar system (not far above the surface of the
sun). Barycentric _coordinate_ time is distinguished from barycentric
dynamical time by accounting for the slowing of time at the barycenter
due to the deeper gravity well. And geocentric coordinate time differs
from terrestrial time by putting the clock at the center of the earth
instead of on its surface.

The IAU was following a squeak-like philosophy; they introduced
official timesystems with gleeful abandon. This has the advantage of
letting us use definitions of time that include our current level of
understanding, and the disadvantage of requiring future generations to
convert from more different historical standards. I hope those future
generations have smart reference streams for importing old papers. :-)

-- 
Stan