Tracking the Moons of Jupiter

(with a telescope)

Tracking the Moons of Jupiter

Jupiter has many moons orbiting it. Four of these are very easy to spot in a small telescope. (They are called the Galilean Moons, because they were discovered by Galileo Galilei.) During the course of at least a week, make at least 8 observations at least 2 hours apart, in which you record the positions of the four Galilean Moons. (Sometimes you will only see three. Can you think why?) The moons are aligned with the ecliptic, so will appear to be moving roughly back and forth on a line through Jupiter.

Equipment Use

You will be using one of the lab telescopes for this project. You need to tell me when your group wants to check out a telescope. Note that this is a telescope project that can be done during a full moon.

Your Data

Very carefully record the positions - the diameter of Jupiter is a good "yardstick". You could also measure the time that it takes for the moons to leave the field of view to get relative distances from Jupiter. To do the timing method:

Get both Jupiter and the moon in question in the field of view at the same time. Leave the telescope stationary so that both objects begin to drift out of your field of view.
Start timing when the first object (it could be either the moon or Jupiter) leaves the field of view. Stop timing when the second object leaves the field of view.
Repeat the timing for each moon that you can see. If the moon left the view first, give that time a negative value. If Jupiter left first, give that time a positive value.
How long does Jupiter take to leave the field of view? You will have to decide which edge of Jupiter you want to use for your zero point.
You can plot your timing data against the day and hour of your measurement. Make the hour of the week your "X" axis, and the time (in seconds) between the two object your "Y" axis.

Your Report

You should follow the format found on the report page. In particular, your Data and Results section needs to have a plot of postion vs. time for the moons you observed. You should also try to identify which moon is which by using the monthly finder charts in either Sky and Telescope or Astronomy magazine, or one the software tools. Try to determine the orbit radius (in Jupiter diameters) and the period (in hours) of at least one of the moons from your data. The more measurements you make, the easier this will be.