Here's why:

* Light-year is a unit of distance: A light-year represents the distance light travels in one year. It's a vast distance, roughly 5.88 trillion miles (9.46 trillion kilometers).

* Our solar system is relatively small: The furthest planet in our solar system, Neptune, is only about 4.5 billion kilometers (2.8 billion miles) from Earth.

* Nearest stars are light-years away: The nearest star system to our Sun is Alpha Centauri, which is about 4.37 light-years away.

While there are many stars and planets beyond our solar system, it's extremely rare to find them within a light-year of Earth.