Telescope or Time Machine?

http://thecareernation.com/scientists-slow-down-the-speed-of-light/

Light travels at a finite speed, which is about 300,000 kilometers a second. To help to understand how fast this is, we say that if light went in circles it could go around earth eight times in just one second.  Even with such a high speed, it still takes light time to travel vast distances. 

http://vesmir.stoplusjednicka.cz/jak-dlouhy-je-svetelny-rok-parsek

The farther we go into space, the longer light takes to reach us. For example, light from the moon takes one second to reach us while light from the Andromeda Galaxy about 2.5 million years to reach us. 

Therefore, when we see the light from these objects, we are in fact looking back in time. When we see the light from the Andromeda Galaxy, we are seeing it as it was 2.5 million years ago. We are looking back in time when we see these far objects in the sky because light can only travel so fast and some of these objects are so far away from us it takes millions or even billions of years to reach us. This topic can be difficult to comprehend, but it is necessary to that when we observe the universe we can not separate space and time. For a lot of objects in the night sky, we are viewing a much younger universe. If a star was to die today, we would not know for years.

http://www.slideshare.net/sarahjones78/the-universe-35449770

Scientist therefore can use their telescopes as a sort of time machine to discover more about the characteristics of the universe in the past. Galaxies take a long time to evolve so we cannot watch a galaxy change overtime. However by comparing past (more distant) galaxies to the (closer) galaxies of today scientist can see how they evolve as seen in the picture below.

http://www.science.tamu.edu/news/story.php?story_ID=1381