4.2 review

Ellipse

An oval-shaped path that planets follow as they orbit.

Eccentricity

A number that tells how stretched out an orbit is (0 = circle, closer to 1 = very oval).

Aphelion

The point where an object is farthest from the Sun.

Perihelion

The point where an object is closest to the Sun.

Orbital period

The time it takes an object to complete one full orbit.

Orbital velocity

How fast an object moves in its orbit.

Foci

Two fixed points inside an ellipse; the Sun is at one focus.

Major Axis

The longest diameter of an ellipse.

Minor axis

The shortest diameter of an ellipse.

Parallax

The apparent shift of an object’s position when viewed from different locations.

What are Kepler’s Three laws?

Planets orbit the Sun in ellipses, with the Sun at one focus, Planets move faster when closer to the Sun and slower when farther away, and the farther a planet is from the Sun, the longer its orbital period.

What is the Equation for Kepler’s 3rd law , and what do the variables mean?

T2=a3, T = orbital period, a = average distance from the Sun (semi

What has a gravitational force?

All objects with mass

What two factors effect the force of gravity?

Mass and distance

What is happening at perihelion?

Planet is closest from the sun and moving the fastest

What is happening at aphelion?

Planet is farthest from the sun and moving the slowest

What has the most elliptical orbits?

Comets

What is eccentricity, and how is it measured?

It measures how oval an orbit is, on a scale from 0 to 1

What model (heliocentric or geocentric) has planets orbiting in ellipses?

Heliocentric model

Where are foci located on an ellipse?

Inside the ellipse along the major axis