Last year, we lost Neil Armstrong. Also, a NASA engineer who had been hand-picked by Werner von Braun to help develop the Saturn V rocket, Jesco von Puttkamer, passed away even more recently.

These events, not surprisingly, inspired some curiosity about the moon, and led to the decision to add a new feat to the Mental Gym, estimating the phase of the moon for any date in the 1900s or 2000s!

You'll need to be familiar with the phases of the moon and other technical terms, so the first section teaches those basics, along with helpful mnemonics.

From there, the next section shows you how to adjust for the month and day. You then learn how to adjust for the century and the year. The year is the only real challenging part, but I do include shortcuts to make this easier.

The 4th section focuses on practice and presentation. Instead of designing a custom quiz for this, however, it turns out that Wolfram|Alpha works well as a quiz.

You start by having Wolfram|Alpha generate a random date. Use the formula to estimate the phase of the moon for that date, and then check yourself by clicking on the date. For example, if Wolfram|Alpha gives you Dec, 1, 2005, you'd work out that it's very close to a new moon, then click on that date, scroll to the bottom, and verify that there actually was a new moon on Dec. 1, 2005! The moon phase feature of Wolfram|Alpha is also handy for verifying the moon phase in performance, of course.

I also include plenty of tips and tools, including shortcuts and handling other centuries.

The method for estimating the phase of the moon is taught as a straightforward method, with little explanation. However, if you are curious, I include an entire section explaining the reasoning behind each part of the formula.

I'll wind up this moon post with a surprising video about the distance from the Earth to the moon, which you may find useful when you present this feat: