Scroll over the [ ]'s to reveal the correct answer.

Lab 13: Orbital Motions of Planets

A galaxy is a collection of [stars], [gas], and [dust] gravitationally bound together.

Kepler's Laws of Planetary Motion

1. [Bodies orbit with elliptical paths]



2. [Orbit sweeps out Equal Area in Equal Time]



3. [Period² (yr) = (Semi-major axis)³ (AU)]

Major Parts of an Ellipse:

Mercury's orbit

The maximum angular distance Mercury appears to reach from the sun as viewed from Earth is also known as its [greatest elongation].

Using Mercury's greatest elongations, the orbit can be found and its shape will be an [ellipse].

This means that the sun [WILL NOT] be at the center of Mercury's orbit.

The point at which is the sun is found is called a [focal point].

Motion of Mars

Most of the time, Mars appears to move in one direction relative to the background stars. This motion is called [prograde] motion.

Occasionally, Mars' motion will reverse. This is called [retrograde] motion.

This motion is due to the difference in angular [speed] of Mars and [the Earth] about the Sun.