Apoapsis

Definition

Apoapsis is the point in an orbit around a celestial body where the orbiting object is farthest from the center of the body. It is a key concept in understanding elliptical orbits.

5 Must Know Facts For Your Next Test

1. Apoapsis is one of the two main points, along with periapsis, in an elliptical orbit.
2. In polar coordinates, apoapsis occurs when the radial distance is at its maximum value.
3. The term 'apoapsis' can be specific depending on the central body; for example, apogee for Earth or apohelion for the Sun.
4. The formula to find apoapsis distance in an ellipse is $r = \frac{a(1+e)}{1+e\cos(\theta)}$ where $a$ is the semi-major axis and $e$ is the eccentricity.
5. Understanding apoapsis helps in calculating orbital parameters such as orbital period and energy.

Review Questions

• What is apoapsis and how does it differ from periapsis?
• How would you represent apoapsis in polar coordinates?
• Which term would you use to describe the apoapsis of an object orbiting our Sun?

Related terms

Periapsis: The point in an orbit closest to the center of mass of the celestial body being orbited.

Eccentricity:

A measure of how much an orbit deviates from being circular; calculated as $e = \frac{c}{a}$ where $c$ is the distance from the center to a focus and $a$ is the semi-major axis.

Semi-Major Axis: The longest radius of an ellipse, running from its center through one of its foci to its perimeter.