Carolyn,
   Yes, you are right, astronomers do indeed include a zero year. They do it
for convenience in their calculations. I have a computer print-out from the
Library of Astronomy at the University of Michigan, giving me solar and
lunar eclipses back to 1000 BC. On the first page it tells the reader to
adjust all the BC dates by one year to make it conform to reality. They know
their dating method is off by one year.

Bonnie