A light year is the distance that light travels in one year. Measured in miles, that distance is 5.88 trillion miles (9.46 trillion kilometers).
Objects in the night sky are far away. By comparison, the distance between Mars and Earth changes as each has its own orbit around the sun, but the furthest that Mars ever gets from earth is 249.1 million miles (401 million km). An object a light year away is over 23,605 times as far as Mars is from Earth at its furthest point.
The closest star to Earth is a triple-star system called Alpha Centauri. The two main stars are Alpha Centauri A and Alpha Centauri B. They are about 4.35 light-years from Earth. A third star called Alpha Centauri C is about 4.25 light-years from Earth, making it the closest star other than the sun. 4.25 light years is about 25 trillion miles from Earth. 25 trillion miles is a long way.
For context, the stars in the Big Dipper range from 78 to 124 light years away.
Time is an additional another element beyond mere distance. The light we see coming from a star left its point of origin in the past. The light from a star, galaxy or nebula takes time to reach us. We are not seeing the object as it is now, but rather as it looked in the past – when it emitted the light. Because everything in space is located at different distances from the earth, the night sky is a historical composite rather than a single snapshot in time.
Photo at McDonald Observatory near Ft. Davis, Texas