You can get students to make their own measurements of this via two sets of resources:
This PDF file includes some exercises on Kepler's 3rd law, gravity, and density. For some of these exercises you will need the data in this Excel file for the dwarf planet Haumea. The Excel file contains data on the brightness of dwarf planet Haumea measured as a function of time on two nights in 2007, by astronomers at QUB. The lightcurve plotted using those data should appear as shown to the left.