Grading: The data that you take and your presentation of them will be worth 10 pts. The hypothesis you present and how well it explains the data will be worth 10 pts.
Some things to think about:
1) What are the kinds of data it will be useful to have? (e.g. position of moon, appearance of moon at different times)
2) Will it be more useful to observe at the same time every day/night, or at different times? Are nightly observations necessary or would weekly observations be sufficient? You have an advantage since you probably already have a working hypothesis for why the moon has phases. Use this knowledge to design your observing program.
3) How will you present the data so that the reader can understand what you observed?
4) How will you present the hypothesis so that the data provides a real test of it?
5) Full moon this month is on Sept. 16, so it would be a good idea to begin your observations soon in order to get a full cycle.