Ever dance with the devil in the reflected sunlight?
Being out under an 80% moon the other night had me thinking about all of our funny assumptions that stem from our altered perceptions of things like the moon and its light. Many people have asked themselves things like “Why does the moon look bigger on the horizon?” (which is a subject for another post) or “If the moon looks white in the sky, why does everything seem blue-ish in its light?”. Well, first off, I’d suggest you read Bad Astronomy (like the blog, by the same dude) and get a more detailed answers to these questions, plus many more. Seriously, it’s a quick, fun read.
First things first though, we need a little perspective. If the earth were the size of a basketball, with a diameter of about 9.4″ inches, then the moon would be about the size of a tennis ball, diameter about 2.6″. This ratio isn’t exact, but it’s pretty darn close. I think we all understand the moon is much smaller than earth, so the size difference shouldn’t be a surprise, but something that does surprise a lot of people is that if you use that sizing scale, the tennis ball moon would orbit our home basketball at a distance of 24′! Note, that’s FEET not inches. This example has been talked and blogged about many times, and there’s even a video:
So, the moon is more distant than we generally think of it being. We all know (right?) that the light we see from it is simply the light of the sun shining upon it and as it goes through its phases, the part that we see is the part that faces the sun. Isn’t it funny then that the parts of the moon that aren’t getting direct light seem totally black? I mean, doesn’t the earth reflect light on the moon, like it does for us? Heck, we’re even way bigger and have stuff like clouds and water that reflect visible light pretty well. WHAT IS THE DEAL?
Well, first of all, the moon is actually much darker than people think. We imagine a light-grey, almost whitish, landscape covered with fine dust that happens to be perfect for preserving astronaut footprints. In fact, while it is dusty, the moon’s surface is darker than asphalt. When we see a full moon, that seems to glow white, it seems crazy to think that the surface could be so dark. Secondly, the moon doesn’t have any mechanisms for spreading the light around, like an atmosphere or casinos. The daytime sky on the moon is black.
To put it in the terms of an earthly example…
Imagine, for a moment, that you get into a serious disagreement with your spouse, so they knock you out, lock you in the windowless car of a freight train, shut the door and hope by the time you wake up, you’re half way across the country and have to live out your days in some remote shanty town where you’ll never forget to empty the litterbox EVER again. Before the train can leave the trainyard though, you come to, in the dark, and the only light you see is coming through a small hole in the floor, through which you can see a tiny spot of asphalt in the sun. That asphalt, dark as asphalt can be, would look VERY bright.
Also, I just remembered that I need to empty the litterbox.
But why, then, does the light from the moon look blue-ish? The key is our eyes, not the light. As our eyes adjust to the dark, chemical changes occur and the WAY we see begins to differ. First we lose our ability to see reds, then other colors, until about all we can make out is a pale, bluish green. This is the faintest color we can see, so now you know why those signs on the highway are colored that way and why “high-visibility” wear is usually a specific shade of neon green, which is THE most visible color to our eyes. If you take a long exposure photo or video of moonlight, you see just as much color as sunlight, which is, in fact, all it is.
This video is not only very beautiful, but illustrates this point well. Don’t believe that’s the moon and not the sun? The stars give away the truth.
Oh, that image up top? That’s the Juno spacecraft’s pic of the earth and moon. Also, one difference between actual asphalt and the lunar surface is that the moon has a special ability to reflect light back towards its source, so it’s like reflective asphalt, kinda. A full moon is about TEN times brighter than a quarter moon as a result.
There you go! Think about this stuff the next time you’re outside and notice the moon, or even if you’re just watching an old Batman movie.