GCSE Science Assessed Practical

Physics - Astronomy

The Moons of Jupiter

The Earth takes 365.25 days to orbit the Sun. Planets further out from the Sun take longer to complete an orbit.

Galileo first turned a telescope to Jupiter in 1610. He found out that there were four moons circling the giant planet. They are called the Galilean satellites in his honour.

Your task is to find out the relationship between the average distance of each moon from Jupiter and the time it takes to orbit the planet.

You will need to research theories about why distances between orbiting objects should effect their orbital period? If you can, use data about Jupiter and its moons to predict the relationship.

Write a plan for your investigation. Use your own observations and/or a planetarium program (e.g. the free program 'Carte du Ciel' from http://www.stargazing.net/astropc/index.html) to gather data about distances and periods. You could use a mixture of the two. Give details about the instruments or programs you will use.

Decide on the number of observations needed to make reliable conclusions. Think about other variables that could affect your results. Remember that you are making observations from a planet that is orbiting the Sun at a different rate to that of Jupiter.

Show your results in a clear form with all units labelled. You may find using a spreadsheet of help in analysis. Display your analysis in a suitable graphical form.

Make conclusions backed up by scientific ideas.

Evaluate your results. Look for any anomalies in your data. Say how more accurate results could be obtained.

Calculating the distance between Jupiter and its moons

The calculation will only work if the moon has reached its greatest apparent distance from Jupiter.

Distance = radians of angular separation x distance in km

There are 206,265 seconds of arc in a radian so calculate radians of separation by dividing seconds of arc by 206,265

A maximum angular separation of Jupiter to Io is measured from the ‘Starry Night’ computer program as 121” on 29.03.03 at 14.16.43. Jupiter distance is taken from the

program as 714900000km.

So the orbital distance of Io is:

121”/206265 sec per radian x 714900000km = 419000km

This is within 1% of the average distance of Io from Jupiter which is given as 421,600km in the ‘Philips Atlas of the Universe 2001 Edition’.