Here's why:

* Kepler's Second Law: This law states that a planet sweeps out equal areas in equal times. This means that the area swept out by the line connecting the planet to the Sun in a given time interval is always the same, regardless of the planet's position in its orbit.

* Area and Velocity: Imagine a planet moving in its orbit. When it's closer to the Sun, the line connecting it to the Sun is shorter. To sweep out the same area in the same amount of time, the planet must move faster. Conversely, when it's farther away, the line is longer, so it moves slower to cover the same area.

* Conservation of Angular Momentum: This relationship is directly related to the conservation of angular momentum. As a planet moves closer to the Sun, its moment of inertia decreases (because the distance from the center of rotation is smaller). To maintain constant angular momentum, the planet's velocity must increase.

This is a fundamental aspect of planetary motion and is essential for understanding the dynamics of our solar system.