Periapsis

Definition

Periapsis is the point in the orbit of an object where it is closest to the focus of its elliptical path. In conic sections, this is specifically relevant to ellipses and hyperbolas.

5 Must Know Facts For Your Next Test

1. In an ellipse, periapsis is one of the two extreme points along the major axis.
2. The distance from the focus to the periapsis is minimum in an elliptical orbit.
3. The formula for calculating periapsis distance in polar coordinates involves semi-major axis $a$ and eccentricity $e$: $r_{peri} = a(1-e)$.
4. For celestial bodies, periapsis relative to Earth is termed perigee, and relative to the Sun, it's called perihelion.
5. In hyperbolic trajectories, periapsis occurs at the closest approach before diverging away.

Review Questions

• What is the significance of periapsis in an elliptical orbit?
• How do you calculate the distance to periapsis using semi-major axis and eccentricity?
• What term describes periapsis when referring to orbits around Earth?

Related terms

Apoapsis: The point in an orbit where an object is farthest from the focus of its elliptical path.

Eccentricity: A parameter that determines how much an orbit deviates from being circular. It ranges from 0 (circle) to values close to but less than 1 (ellipse).

Semi-Major Axis: $a$, representing half of the longest diameter of an ellipse, crucial for defining orbital size.