Our own experience has shown that students who use the standard lunar phases diagram in a tutorial session to work out several examples quickly ascend the learning curve to mastery. For various reasons, though, not all students make it to the tuturial sessions, no matter how conveniently they are scheduled. This interactive Java tool was developed to provide an alternative means to that same mastery. The opportunity to make one's mistakes in the privacy of a computer session is attractive to many students. And, of course, by making this tool available via the internet, a much broader range of students have the same learning opportunity my own students have with no additional overhead.
The pedagogical plan is straightforward. First, the introduction presents the basic physical model for the observed phenomenon. The three tutorial pages introduce the elements of the lunar phases diagram one-by-one. The interactivity in these pages allows the students to ask the questions, affording them the opportunity to be certain they understand how the diagram is organized and labeled. These first four pages make the site self-contained for those with no textbook or lecture.
The heart of the site is the "Tool and Quiz" page. Here the student is presented with a problem in which two of the three observables (time of day, time of month, and direction) are given and the third must be deduced. The students can use the interactive diagram tool to solve the problem. Once they choose an answer, the dialog box gives immediate feedback. If a student requires more than one trial to answer correctly, the next problem will again seek the same type of information . On the other hand, a correct answer on the first try will be followed with a problem seeking a different observable. Hence, if a student solves three consecutive problems on the first try, the three problems will have represented all possible types of questions, and the student may conclude he or she has mastered the topic. Some students will reach this point in 5 minutes, others after a much longer period. But with a well defined point of mastery, every individual knows when to stop and when to keep going.
Students who already have a general understanding of the lunar phases diagram will probably want to begin directly with the "Tool and Quiz". Likewise, given appropriate projection facilities, the "Tool and Quiz" can be directly used in a lecture presentation.
The "Going Beyond the Basics" page is for the advanced students who realize the lunar phase diagram is only an approximation of reality. The contents of this page point to the issues they may want to pursue further elsewhere.
Finally, we note how the Lunar Phases Web Tool combines the strengths of the internet: interactive graphics, intelligent drill, and the accessibility of the web. In so doing, it becomes a learning resource that is qualitatively different from those of alternative media (books, lectures, etc.). We hope that by its example, it will stimulate the development of other web tools that likewise go beyond the mere translation of other media into html.