More Than a Circle: Elliptical Orbits Explained Quiz

If an orbit is not a perfect circle but is instead a slightly flattened oval, and if geometry defines this specific oval shape as an ellipse, then the orbits are described as ellipses.

If gravity and momentum balance in a way that allows the distance from the star to change during a revolution, and if a perfect circle requires a constant distance at all times, then the shape must be an ellipse rather than a circle.

If a circle has one center point, and if an ellipse is an elongated shape that requires two specific reference points to maintain its geometry, then those two points are called foci.

If historical records show that Johannes Kepler used data to calculate planetary positions, and if his First Law explicitly states that orbits are ellipses, then he is the individual who proved the concept.

If an ellipse has two foci and the Sun occupies one, then the planet's distance must change as it travels; if the distance changes, the gravitational pull varies, which then causes the speed to vary.

If Kepler's First Law defines the Sun's position as being at one of the two foci, and if the foci are shifted away from the geometric center of an ellipse, then the Sun cannot be in the center.

If eccentricity is a value between 0 and 1 used to describe a curve, and if 0 represents a circle while values closer to 1 represent longer ovals, then it measures the "stretch" of the orbit.

If astronomy motion questions ask for the name of the closest approach, and if the Greek root "peri-" means near and "helios" means Sun, then the correct scientific term is perihelion.

If the prefix "ap-" or "apo-" means away from, and if perihelion is already defined as the closest point, then aphelion must be the point in the orbit where the planet is furthest from the star.

If Kepler's laws describe the geometry and timing of orbits, then the shape, the varying speed, and the orbital period are all valid parts of his mathematical work.

If eccentricity measures how "un-circular" an orbit is, and if Earth's eccentricity is very low at 0.017, then the shape is a very "round" ellipse that appears almost like a circle.

If eccentricity measures the stretch of an ellipse, and if a value of 0 means there is no stretch at all, then the two foci must overlap at a single point, which creates a perfect circle.

If an ellipse has a long side and a short side, and if the long side represents the full length of the orbital path, then that dimension is called the major axis.

If a planet is moving at high speed, it wants to travel in a straight line; if an inward pull is needed to bend that path into a closed loop, then gravity is the force providing that pull.

If an orbit results from gravity interacting with motion, then the speed, the mass of the star, and the direction of travel are the only physical factors that decide the final orbital path.

If an ellipse is defined by the distance between two foci, and if those two foci move closer until they are in the exact same spot, then the resulting shape is a circle; thus, a circle is just an ellipse with zero stretch.

If gravity pulls harder when objects are close together, then the planet accelerates at perihelion; if the pull is weakest when objects are far apart, then the planet must move slowest at aphelion.

If the major axis is the full length of the ellipse, and if "semi" is the prefix for half, then the distance from the center to the edge is the semi-major axis.

If the definition of an ellipse includes an oval shape and a focus that is off-center, then it follows that the distance and speed must change as the planet moves around the loop.

If a value of 0 represents a perfect circle and a value of 1 represents a straight line, then a very long and skinny oval must have an eccentricity value that is very high and close to 1.