Final answer:
Looking at distant stars and galaxies allows us to observe them as they were in the past because light takes time to travel. The Andromeda galaxy, for example, is seen as it was 2.5 million years ago. This aspect makes astronomy a tool for studying cosmic history and galactic evolution.
Step-by-step explanation:
Staring at a star that is three million light-years away is akin to looking back in time because the light we observe took three million years to reach us. The finite speed of light, which is about 186,000 miles per second, means that astronomical observations are essentially historical records. We see the Andromeda galaxy, for instance, as it was 2.5 million years ago, and even more distant galaxies as they were billions of years ago, allowing us to reconstruct and study the cosmic history and galactic evolution by observing remote galaxies from when the light left them, which could be over 10 billion years ago.
The beauty of astronomy lies in its ability to reveal the past state of the universe; this unique characteristic can pose challenges due to the uncertainties in data, but it also enables fascinating discoveries and contributes to the field's ongoing golden age.