How do perihelion and aphelion describe a planet’s changing distance from the Sun?

In celestial mechanics, planets move in elliptical orbits with the Sun positioned at one of the two foci. Because these orbits are not perfect circles, a planet's distance from the Sun changes throughout its revolution.123

• Perihelion: This is the point in a planet's orbit where it is at its closest approach to the Sun.14
• Aphelion: This is the point in the orbit where the planet is at its farthest retreat from the Sun.14

Together, these two points define the line of apsides, which serves as the major axis of the orbital ellipse. According to Kepler’s second law, a planet's orbital velocity is not constant; it travels faster than average when near perihelion and slower than average when near aphelion. The terms are derived from the Greek word helios (sun), with the prefix peri- meaning "near" and ap- (from apo-) meaning "away from".1456