Expert: Jane Tang - 8/30/2006

Question
Hello Jane: I have a pretty good handle on astronomical distances
and time. But please answer me this: Even considering the vast
distances that separate stars from each other and the amount of
time its taken for them to appear to us as they do, since the
universe has been expanding so fast and everything moving away
from everything else for so long, do the positions of the stars as we
see them today differ at all from how they appeared 500, 1,000 or
2,000 years ago? If only they had accurate methods of measuring
as we do now there'd be a experiential way of knowing. AND, if
there is no appreciable difference, how many years would it take til
there WAS a difference?  Thanks for being available!

Answer
Hi,
    The first question is very complicated. I would say Yes and No. If the objects (stars, galaxies, ...) are not gravitationally involved with each other, then their distances are larger and larger because of the expansion of our universe. But if the objects belong to one gravitational system, for example, stars in Milk Way, their distances do not change. Image the Solar system, the distances between the Sun and the planets cannot be changed by the expansion.

    The age of the universe is around 15 billion yrs, so I would say that the time scale is around 0.1 billion yrs to 1 billion yrs.
    Sorry for this late answer. But the network in our group broke down yesterday and the day before yesterday.

      J