It takes the number of years that the star is away from earth, in light years. This ranges from about 4 years (Alpha Centauri) to 14 billion years. Most stars are many thousands to hundreds of millions of light years away.
Rigibson’s answer is great, but, just to add some perspective, traveling at light speed (186,000 miles/second), light from the Sun reaches the Earth in 8 minutes! The closet star besides our Sun is about 4 light years, that is, the distance it takes for light to travel in a year, away. Stars in other galaxies are millions and billions of light years away! By the time their light reaches Earth, these stars could be dead. These distances are unfathomable.
Speed is equal to distance divided by time, and time is equal to distance divided by speed. Light travels at about 300 million meters per second, and then from there, we measure distance in light years, or AMUs. We get light 8 minutes old from the sun, as well as light trillions of years old from stars at the beginning of the universe.
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