The Friday Fillip: Lunacy

The moon today is waning gibbous and 95% of full — whether or not you can see it through the rain or past the city lights where you are. I suspect that, if you’re at all like me, you don’t often look up and note old luna’s phase. Nor, I suspect again, are you likely able to say just by looking at the image on the right whether the moon’s on its way to or from full. That fact struck me the other day; not only have we in the city — and, I dare say, in nearly all of modern society — lost any practical understanding of the stars in the sky (Can you find polaris, the “north star”?) but also even simple knowledge of the Earth’s only satellite. It staggered me a little.

If you feel any inclination whatever to remedy your lack of knowledge — or that of your children, perhaps — you might turn to MoonConnection.com. They’ll try to sell you some software, but they’ll also offer you a host of informative and interesting features. So, for example, there’s the Moon Phases Calendar, which pictures the moon on every day of the month (and year) of your choice. And there’s a particularly clear visual explanation of how the moon comes to be seen in phases from the Earth.

The lunar cycle has names for eight of its states: full, is when there’s no shadow; waning gibbous, describes a moon that is more than half visible, but shrinking; third quarter is a half visible moon (Which half?) on its way to a crescent; waning crescent is fairly self explanatory; and new, which somewhat oddly is no moon at all. We then build back up in the same stages: waxing crescent, first quarter waxing gibbous, full… And so it goes.

If you’re ready for something more challenging, take a look at Wikipedia’s treatment of the moon. Here there be perigees, apogees, eccentricity, synchronous rotation and much, much more.

But if you’re content to learn just one simple thing, learn which way the shadow moves across the moon. That is, learn how to know when you gaze at it whether it’s waxing or waning — recognize, that is, that the graphic above shows a waxing crescent. I certainly intend to do just that, and so I’ve developed a mnemonic: shadow to the left, expect more heft; shadow to the right, say goodnight. After the jump, there’s an animated gif that shows the phases speeded up and gives you something to contemplate as you drive home the lesson.