A planet travels faster when it is closer to the sun in its elliptical orbit. This is due to Kepler's Second Law of Planetary Motion, which states that a planet sweeps out equal areas in equal times.

Here's why this happens:

* Conservation of Energy: A planet's total energy (kinetic + potential) remains constant throughout its orbit.

* Near the Sun: When the planet is close to the sun, its potential energy (due to its distance from the sun) is lower. To maintain constant total energy, its kinetic energy must be higher, meaning it moves faster.

* Far from the Sun: When the planet is far from the sun, its potential energy is higher. To maintain constant total energy, its kinetic energy must be lower, meaning it moves slower.

Therefore, the section of an ellipse where a planet travels faster is the portion closer to the Sun (called the perihelion). The section furthest from the Sun (called the aphelion) is where the planet travels slowest.