Final answer:
When we look at light from astronomical objects, we're seeing them as they were in the past due to the time it takes for light to travel from the source to us, allowing astronomers to study the evolution of the universe.
Step-by-step explanation:
When we look at light from an object in the sky, we are in essence looking into the past. This is because light travels at a finite speed, meaning that the light we see from distant objects has taken time to travel from its source to our eyes. For instance, when we observe the Sun, we are seeing it as it was 8.3 minutes ago because its light takes that long to reach us. Similarly, when we observe the Andromeda galaxy, which is 2.5 million light-years away, we're seeing light that left it 2.5 million years ago.
The phenomenon of the delay in the arrival of light allows astronomers to understand how the universe appeared in the past and study its evolution. For example, observing galaxies that are billions of light-years away provides a view of the universe when those galaxies were in their formative stages. However, it must be noted that the distances involved introduce great uncertainties in our observations, leading to many questions and competing theories in the field of cosmology.