Moon Week: That's Amore

Thursday, July 02, 2009

As you've probably heard, NASA launched the Jackson V yesterday - we're finally going back to the Moon! To celebrate, I'm dedicating a week to facts about our closest and third-largest satellite.

We all know that the light we see from the Moon actually comes from the Sun, and that the Moon is merely a reflector. That's all fine and dandy during the day, but if that's all there is to it, how can we possibly see it at night? The answer lies in the Moon's chemical composition.

As it turns out, Moon dust is composed largely of strontium aluminate - the same compound used in "glow-in-the-dark" materials. If you've ever had a glow-in-the-dark watch, you know that it only glows once it's been "charged" by holding it under a light. The Moon works exactly the same way. During the day, it absorbs light energy from the Sun and stores it. At night, it releases this energy as visible light.

I know what you're thinking: "But Dan, glow-in-the-dark stuff is green, and the Moon is white!" There are a couple of reasons for this. The first is that the strontium aluminate on the Moon is a much higher concentration than what we use here on Earth, so the light emitted is much brighter.

The second reason is that the light is filtered by our atmosphere. You know how the sky adds a red tint to the Sun's light during sunset? Well that doesn't stop just because the Sun goes away. Any light that passes through the atmosphere during the night is heavily tinted, which causes the pale-green Moon to appear white.

An interesting side note: We have the glow-in-the-dark industry to thank for this new expedited mission. Artificially synthesizing strontium aluminate is prohibitively expensive, and we're quickly running out. The Jackson V will bring back 750 metric tons of Moon dust - enough to last us almost 10 years!

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