Stargazing is a lovely hobby—if you live in a place where you can see the stars, that is—but what you see is the past. Einstein’s relativity theory postulates that nothing can travel faster than light. To understand why you see the star in the past, let me give an analogy.
Imagine times where kingdoms had to dispatch messengers. Suppose a king is down with a mysterious sickness, and the only doctor who can cure him is very far away. The king dispatches a messenger. More often than not, the doctor doesn’t receive the message on time. This is because the message cannot travel any faster than the messenger.
A star communicates to us through its light; you see the star because it’s emitting light. So if light cannot travel faster than 299792458 m/s – the measured speed of light, then the information it carries cannot travel any faster.
Suppose a star is due to die in two days and say it’s so far away that light from the star takes seven days to reach us. When we receive the light seven days later, we perceive there is a star emitting the light. This perception forces our brains to visualize a star in the sky. But there is no star; it died five days ago.
Try musing over this the next time you stargaze.
Rookie Physics 