Question

Explain your reasoning with one or more complete sentences. When we say that a planet has a highly eccentric orbit, we mean that (a) it is spiraling in toward the Sun. (b) its orbit is an ellipse with the Sun at one focus. (c) in some parts of its orbit it is much closer to the Sun than in other parts.

Short answer

Option (c) is correct: a highly eccentric orbit means varying distances from the Sun.

Step-by-step solution

Understanding Orbital Eccentricity

Orbital eccentricity measures how much an orbit deviates from a perfect circle. A low eccentricity means the orbit is almost circular, while a high eccentricity indicates a more elongated shape.

Identifying the Key Characteristics of Eccentric Orbits

Observe that as eccentricity increases, the stretching of the orbit becomes more pronounced. This means that the distance from the Sun at different points in the orbit can vary significantly.

Recognizing the Correct Choice

Considering this characteristic, option (c) is correct. A highly eccentric orbit means the planet is much closer to the Sun in some parts of its orbit than in others due to its elongated elliptical shape.

Key concepts

Elliptical Orbits

In the world of astronomy, understanding the shape of a planet's path around the Sun starts with grasping the idea of elliptical orbits. An ellipse is a geometric shape that looks like a stretched circle. Unlike perfect circles, ellipses have two focal points or "foci." In the case of planetary orbits, the Sun sits at one of these foci.
How can we tell an orbit is elliptical? We measure something called eccentricity. If an orbit's eccentricity is zero, it is a perfect circle. As eccentricity approaches one, the ellipse becomes more stretched out. This is why we say that planets with highly eccentric orbits have paths that are more "elongated." These elliptical orbits are not just abstract paths; they influence a planet's speed and distance from the Sun throughout its journey. At certain points along the orbit, particularly where the planet is closest or furthest from the Sun, interesting changes happen such as shifts in speed and temperature which can affect planetary climate and conditions.

Planetary Motion

Planetary motion isn't random; it follows specific rules and patterns. Every planet in our solar system moves in a regular and predictable path due to the gravitational pull of the Sun. This predictable movement is what allows scientists to calculate planetary positions even hundreds of years into the future.
One of the essential aspects of planetary motion is its eccentricity. A planet with a highly eccentric orbit doesn't revolve around the Sun in a neat, tidy circle. Instead, it travels along an elongated elliptical path.

• When it is close to the Sun, known as perihelion, it moves faster.
• As it swings to the far side, or aphelion, it slows down.

This variation in speed results from the gravitational forces at play, where the Sun's gravity pulls more strongly at closer distances. This concept illustrates how gravity plays a key role in guiding the dance of the planets around the Sun.

Kepler's Laws

Johannes Kepler, a smart guy from the 17th century, formulated three laws that describe how planets orbit the Sun. These laws remain fundamental in understanding celestial mechanics today. First Law (Law of Ellipses): Each planet's orbit around the Sun is an ellipse, with the Sun at one of the two foci.
Second Law (Law of Equal Areas): A line connecting a planet to the Sun sweeps out equal areas in equal time intervals. This law indicates that a planet travels faster when it's closer to the Sun and slower when it's further away.
Third Law (Harmonic Law): The square of a planet's orbital period (how long it takes to go around the Sun once) is directly proportional to the cube of the semi-major axis of its orbit (the long part of the ellipse). This tells us how the size of an orbit affects a planet's year length. These laws not only act as a guidebook for planetary motion but also enhance our understanding of orbital eccentricity. Recognizing these principles helps us comprehend why planets don't simply circle the Sun, but instead follow intricate elliptical paths. Each law contributes valuable insights into how speed, distance, and gravitational forces play their part in the cosmos. Understanding Kepler's laws is like having a map that outlines the journey of planets in our solar system.