Galactic Structure: Do Astrophysicists See Stars Where They Are Now?

[TShock]

when astrophysicists study the structure and rotation of galaxies do they take into account that we are seeing the stars in it where they were at different times, we aren't seeing them where they actually are now? Say stars on the closest edge are 100,000 light years away but stars on the furthest edge are 165,000 light years away so that the current structure of that galaxy would look different than what we are actually seeing? Does that make sense to anyone?

 

[Astronuc]

when astrophysicists study the structure and rotation of galaxies do they take into account that we are seeing the stars in it where they were at different times, we aren't seeing them where they actually are now? Say stars on the closest edge are 100,000 light years away but stars on the furthest edge are 165,000 light years away so that the current structure of that galaxy would look different than what we are actually seeing? Does that make sense to anyone?

Well the distances to individual stars does affect 'when' we see the light, but those distances will depend not on the dimensions of the galaxy, but the angle (orientation) of the galactic plane with respect to us (the observers).

I believe astronomers favor those galaxies whose planes are perpendicular to us. As the galactic planes tilt away, then the time differential of observed light increases in width with the angle, so one would have to consider that.

However, looking at galaxies in the 'most favorable' orientation, one may notice little change over some length of time.

The caveat is that we haven't really looked very long at the universe with respect to cosmological times, and we only started look way far away (Hubble Ultra Deep Field) in 2003.

from September 3, 2003 through January 16, 2004. It is the deepest image of the universe ever taken in visible light, looking back in time more than 13 billion years.

http://en.wikipedia.org/wiki/Ultra_Deep_Field

What will be interesting is to look at HUDF in 100, 200, . . . 1000 years to see what has changed. However, none of us will be around.