Planets further from the sun take longer to orbit due to Kepler's Third Law of Planetary Motion. This law states that the square of a planet's orbital period is proportional to the cube of its average distance from the sun.

Here's a breakdown:

* Orbital period: This refers to the time it takes a planet to complete one full orbit around the sun.

* Average distance from the sun: This is the average distance between the planet and the sun, often measured in astronomical units (AU).

The relationship:

* The farther a planet is from the sun, the weaker the sun's gravitational pull on it.

* With a weaker pull, the planet moves slower in its orbit.

* Because the planet is moving slower, it takes longer to complete a full orbit.

Example:

* Earth is 1 AU from the sun and has an orbital period of 365.25 days.

* Mars is further out, at 1.52 AU. Its orbital period is 687 days, significantly longer than Earth's.

In simpler terms: Imagine a planet as a ball on a string, being swung around a central point (the sun). The farther the ball is from the central point, the longer the string, the slower it moves, and the longer it takes to complete a circle.

This is why planets further from the sun have longer orbital periods!