Expert: Paul Wagner - 9/13/2010

Question
I am an ordinary person, not study astronomy or physics, but I love science. I have a question, every time I hear that if we look at the cosmos we are looking to the past, I never understood that.
Correct me if I'm wrong. What the astronomers saying is somewhere in the cosmos if "they"  looked in our direction "they" can see the collision 65 million years ago that dinosaurs Became extinct by an asteroid? What they would see specifically? And what is the relationship between what they would see and the reality on earth now and that Time? Nothing, right? :) What they can conclude with that information?
Thank you for you time.


Answer
HI Sheila

It may seem a bit hard to believe, but the distances in astronomy are so huge that it take light a long time to cross them.  So when we look at the sun, we are actually seeing it's light about 8 minutes after the light left the sun.  So in that sense we are "seeing" the sun as it was eight minutes ago.  For a galaxy 65 million light years away, we are seeing the image of that galaxy as it was 65 million years ago.  

But here's the tough part---Earth, from that far away, would be so tiny that you couldn't really see any detail at all.  So if you were far enough away to see what happened 65 millions years ago, you would be too far away to see the Earth. Most of the planets we have discovered that are outside the solar system are less than 1,000 light years away--inside our own Milky Way Galaxy.  The Andromeda Galaxy is only 2.5 million light years away, so your observers would have to be in a galaxy far beyond that one!   You can imagine how far 65 millions light years must be!

Sorry, but our best ideas of what happened on Earth 65 million years ago will have to come from physical evidence--not astronomers from a distant planet!

Hope that helps

Paul Wagner