Apr 152011
Full Moon Atlas

Does the moon spin?  Yes.  It rotates once on its axis approximately every 29.5 days.  This is why we always see the same face of it, because it rotates once about the Earth’s axis in the same period.  Does the moon rotate?  Well, if you look down (or up) at one of the polar axes, it will rotate about the axis – this is the same as “spin” so, I suppose yes, the moon rotates.  Does the moon flip?  Reverse?  Mirror image?  Transmogrify?

I think this is getting complicated…

When you look up at the moon, you are looking at the world through your eyes.  They are Time Machines just like the Astropotamus’s Time Machine, but they are smaller and work differently.  You see the light from the sun that bounced off the surface of the moon about 8 minutes and 15 seconds ago.  But if you could see the actual image that those photons make inside your eye, it would be upside down.  Your brain gets involved and flips the image right side up so you see in your head the same thing that exists in the real world.  (Don’t start with me on reality versus perception.  Just go with this for a minute.)

Cameras do the same thing.  When you take a picture of something, the picture is made upside down and then printed or electronically converted to right side up so that it comes out as we expected it – the tree grows up from the ground, not down from it.  Same with taking a picture of the moon – the spots and craters and light and dark areas on the moon match what we see with our eyes if we had really good vision when we take a picture with just a camera aimed at the moon.

But remember, Time Machines work like your eyes.  They flip the image.  They just don’t have the same benefit of a brain to flip it back automatically.  What’s worse, sometimes the Time Machine sends the light out at an angle through a reflector that mirrors the image as well.  So sometimes the image is right side up (if you have a right side up angle thingy) and sometimes it’s mirrored (if you have a non-right side up angle thingy) and sometimes it’s flipped, mirrored, rotated 180 degrees and all sorts of things.

To further complicate things, most cameras have a rectangular field of view, but the view through a Time Machine is mostly round.  So you can usually rotate the camera to get a better view in the camera without having to move the Time Machine (which might be hard, depending on how it’s configured and what you’re looking at).  This introduces yet another rotation in the final image!

Combine all these things together and you can have a very confusing view of what the moon looks like through a Time Machine as seen by a camera.  Search Google for “moon image” and you’ll see some that are right side up, some that are rotated, some that are upside down, and some that are flipped left to right.  Even my moon images suffer from lack of proper rotation sometimes.  (But don’t tell anyone.)  It can be quite confusing!  And don’t even get me started on RAW versus JPEG or white balance or color correction or dark frames or light frames or any of the million things that you can do to an electronic image once it’s on the computer!

Luckily, lots of people (and robots) have taken lots of images of the moon.  And some really smart people put them together in a way that they have the same colors, the same brightness, the same “up” and the same “down.”  It’s called the Full Moon Atlas, and you can explore the surface of the moon without leaving your armchair.  Use it to learn how the moon looks normally, and then you can spot the pictures where it doesn’t look right!  Happy selenological studies!*

*Selenology is the study of the moon.  Selenologists are people who study the surface (and other aspects) of the moon.