Hi Tarkus,
Sorry it’s taken so long to write back. I’ve got a 7 year-old who is VERY excited by Halloween.
You are correct that most of the far side of the Moon was in shadow at the time AS16-M-3021 was taken:
However, look at this polar view:
Everything above the red line is technically the far side.
The orange line shows the longitude (103.7° East) that Apollo 16 was over at the time the photo was taken.
As you can see, part of the far side was still in daylight, and that is the part that Apollo 16 was over. Apollo 16 wasn’t behind the Moon at the time; it was off to one side – but it could see part of the far side (it could also see the Earth from where it was).
Now then, projecting a 3D situation onto a 2D monitor causes problems. In this case, the circumference of the Moon in the polar view, above, is the equator (0° latitude) and Apollo 16 was over 12° North at this time, so to show this in the above picture the right end of the orange line should be ~1cm above the surface of your monitor.
If you don’t mind, I’m going to tilt the point of view so that the plane of Apollo 16’s orbit matches the plane of your monitor, and rotate it so that the line to the spacecraft is level, because believe me, drawing these things with MS Paint is a real bitch.
There. Now you can see the path Apollo 16 took after the Trans-Earth Injection (TEI) burn that sent them home. At the time AS16-M-3021 was taken, Apollo 16 was ~1,200km above the surface of the Moon (I think someone asked that a few pages ago).
As I explained in my previous post, from this close to the Moon, the horizon is much closer so that, although you see the Moon as a sphere, you don’t see an entire hemisphere. You can test this for yourself by holding a fútbol at arm’s length, and then bring it closer to your eye. For a regulation FIFA fútbol, your eye would have to be ~7.5cm from the surface of the ball to correctly model the distance from Apollo 16 to the Moon’s surface.
In the above illustration, only that portion of the Moon inside the orange triangle can be seen in AS16-M-3021, and (as you can see) most of that is in daylight.
The illustration below re-centers the point of view over 12° North, 103.7° East, the spot Apollo 16 was over:
On the left is the ~orthographic view, showing the whole hemisphere centered on 12° North, 103.7° East. Because of the shortened horizon, only the area within the orange circle could be seen – and most of this is in daylight. The right-hand image is the view from 1,200km above the surface, and it matches AS16-M-3021.
Note that in this picture, I’ve drawn the 90° East longitude line (Please excuse the crude-ness - it's hand-drawn with MS Paint, but is accurate to within a few pixels). To the left of it is the near side visible from Earth. To the right of it is the far side.
So, in summary:
- Most of the far side was in shadow, but not all of it.
- Apollo 16 was not behind the Moon at the time AS16-M-3021 was taken, but rather was off to one side.
- Apollo 16 was over a part of the Moon that was still in daylight.
- From where it was, Apollo 16 could see parts of both the near side and the far side of the Moon.
If any of this is confusing, just look at the pictures again. Hope this helps. Cheers!
