Which of the following is true regarding the orbits of planets?

The correct answer highlights that the orbits of planets are elliptical, meaning they are oval-shaped rather than perfect circles. This elliptical nature was first described by Johannes Kepler in the 17th century, particularly in his First Law of Planetary Motion. According to this law, a planet's distance from the sun varies as it moves along its orbit, resulting in varying speeds at different points. When a planet is closest to the sun, it moves more quickly due to stronger gravitational attraction, while it slows down when it is farther away. This variability in distance and speed is a fundamental aspect of planetary motion and helps to explain the dynamics of planets within our solar system and beyond.

In contrast, the other options present misunderstandings of planetary motion. The idea that all planets orbit in perfect circles simplifies the reality of elliptical orbits. The claim that orbits are not influenced by gravitational forces contradicts the fundamental principles of gravity, which govern celestial movements. Lastly, stating that all orbits are the same length ignores the fact that different planets have different orbital periods and distances from the sun, thus each having unique orbital characteristics.