This lab exercise is intended to provide you with insight into major planetary features as well as an understanding of the sizes of these features. You will asked to examine a number of planetary images - these will be available in both paper form (to include as part of your report) as well as in electronic form for analysis using on-line tools.

Materials and Resources

  • access to Stellarium
  • access the applet Planetary Scale Calculator
  • a graphics tool such as Gimp or Microsoft Paint
  • paper copies of planetary images from The King's University Observatory


  1. Please select images from the following sets. Be sure to note the image scale that is shown in the table below. When the image is displayed "right-mouse-click" on the image and save it to your local hard drive (make sure you note which directory it is being saved in!) - it would be a good idea to save it into your "My Documents" or "Downloads" folder.
Image Set Image Info Image
M Mars, January 16, 2010. Image scale = 0.24"/px
J Image J1: Jupiter on the evening of November 5, 2011. Image scale is 0.29"/px
J Image J2: Image taken evening September 29, 2011. Image scale is 0.29"/px
J Image J3: Image taken evening Dec 26, 2009. Image scale is 0.43"/px

Saturn. Image taken evening of January 26, 2009. Image scale is 0.16"/px




(Image by Torsten Hansen)

  1. Open your favourite image analysis program as well asPlanetary Scale Calculator. You will need these to help analyze your planetary images.
  2. Use Paint (or similar program) to open one of the images that you have saved in your "My Documents" folder
  1. Be sure to look up the distance between the earth and planet for the night on which each image that you choose was taken. Use Stellarium to do this. The distance will be given in AU. You will also need to enter the scale of the image in seconds or arc per pixel ("/px). Finally, enter the size of the feature in pixels and press the calculate button. (Note: to review steps 3 and 4 you may find it useful to go back to the moon lab - follow this link.)


For each of the images that you chose please do the following:

  1. Prepare a table in which identify by letter or number features on the images that you wish to measure. Carefully note this on the hard copy (which may be handed in along with the report) as well as in the table. Be sure to record the image scale and the size of the feature in both pixels and kms.
Image Name
scale = ("/px), Distance (AU)
Feature Size (px) Size (km)
  1. Specific Tasks:

    Image Set and Image# Tasks
    M; Mars Measure diameter and 2 other significant features of your choice

    Measure diameter and width of zones and belts (be sure to note which ones on your hardcopy or electronic image)

    Measure 2 other features (be sure to note them on your image)

    J2 Measure size of Great Red Spot

    Measure diameter of the moon Ganymede

    Measure oblateness of planet (see below)

    J3 Measure distance of the 3 moons from planet and explain why these are all under estimates of the true orbital distance.
    S; Saturn

    Measure diameter and oblateness of planet

    Measure extent of the rings


You will easily see that both Jupiter and Saturn are not round but oblate. This means that the diameter measured along the equator will be different than the diameter measured from "pole-to-pole". If Dequator = the diameter at the equator and Dpolar = the polar diameter then the oblateness 'o' is defined by the expression:

What to Hand in and When

The entire lab project (Moon and Plantes) is due in 1 week and combines the work that you did previously with in the "Measuring the Moon" exercise. Please include a cover page and a data section in which you present your tables and paper copy images. Under a separate heading discuss the questions posed in the Analysis section. Please do not put these in a list and answer them that way! Rather, encorporate those answers into an actual discussion of what your data mean. It may be helpful to organize your discussion under helpful sub-headings. The exercise will be graded as follows:

Neatness and format:

  • Useful headings
  • grammar and spelling
  • typed and followed format

Discussion of Data

  • number of features discussed
  • insight into the features and what they mean
  • variety of lunar features that you investigated


  • what insights about lunar and planetary origins does your data suggest - spend some time discussing what you have discovered and suggest other things that the data may tell us.