Planets and Satellites: Activity 2

ACTIVITY 2: ORBITS

Concepts:

geometry (radius, circumference of circles)
division
graphing
analyzing data
structure of the solar system

Activities: Using the attached table of values, make two graphs:

orbital period versus distance from the sun (orbital distance)
rotational period versus distance from the sun

Interpretation:

Orbital period is how many days it takes for a planet to go around the sun.
Q: The orbital period of the Earth is about 365 days, what is this?
A: one year
Q: How long is a year on Venus?
Q: How old are you in Mars years?
Q: How many Earth years go by before one Jupiter year has passed?
Q: What trends do you notice in looking at your graph of orbital period vs. distance from the sun?
A: orbital period increases as distance from the sun increases
Q: Why do you think this is?
A: (hint - draw a picture) Planets farther from the sun have more distance to travel to go around the sun once -- their orbits have larger circumferences (2*[[pi]]*r).
Rotational period is how long it takes for a planet to spin once on its axis, like a top (but much slower!).
Q: How long does it take the Earth to rotate once?
A: 24 hours
Q: What is this period of time called?
A: 1 day
Q: How long is a day on Jupiter? on Venus?
Q: What planet rotates the fastest? The slowest?
A: Jupiter, Venus
Q: Do you see any relationship between distance from sun and rotational period?
A: there isn't really any
The "retrograde" next to the rotational period for some of the planets means that they rotate backwards, compared to the rest of the planets.
Q: Which planets have retrograde rotations? (backwards spins)
A: Venus, Uranus, Pluto

Scientific context: No one really knows why Venus rotates so slowly. One suggestion is that early in its formation, it was hit by a huge body coming from a direction opposite its rotation, and that this slowed down its rotation immensely, as well as making it spin backwards.

Try this out with a beach ball and your hand: spin a beach ball (or a globe with a fixed base), and see if you can push it with your hand in the opposite direction from its spin. The spin slows down, and if you push hard enough it'll start spinning in the other direction.

Uranus is another anomaly: it not only spins backwards, but it also spins on its side, like it was hit from the side by a giant impact. The study of giant impacts and their importance in the early days of the formation of the solar system is a current field, and many scientists use clues like rotation rates and direction of spin axes to make guesses about what happened long ago.

[references / further information / links]

Back to Activity 1 or Forward to Activity 3

This module was written by Cynthia Phillips, Dept. of Planetary Sciences, University of Arizona, Tucson AZ, and funded in part by the NASA Spacegrant program.

Questions, comments, and suggestions welcomed: cphillips@noao.edu or phillips@lpl.arizona.edu.