Re: Stereo of the Moon

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

(OK, others wrote and commented on some of this but not all of it and rather
than re-write the whole thing here it is ...)


> RJ Thorpe writes:
>>............ snip ...............
> Then the ratio would be 8000:250,000 or about 1:30 which is
>>what I think we shoot for. Any comments?
>

> Dr. George T. Comments:
>Yes.  Assuming that your numbers are correct, 1/30 is the ratio of the
>diameter of the earth to the distance of the moon.  So, if someone was
>standing at one end of the earth and took picture of the moon at moonrise
>and someone else was standing at the other end of the earth and took
>another picture at moonset _at the same time_, then we would have a good
>stereo of the moon.
>
>But, if the same person is going to take two pictures at different times
>from the same location in a 12 hour period, we are talking about a
>different situation.  The moon has the bad habbit of showing us the same
>face at all the times, which makes stereo of the moon _from the same
>location_ impossible.  
>
>Well, almost.  It is this "almost" (small variations in the rotation of 
>the moon) that make the stereo of the moon from the same location not
>impossible, but just difficult.
>
>George Themelis, at photo-3d, stereo lunch break...
>
>...once wanted to be an amateur astronomer but 3d killed that too! 
>
>

The moon shows the same face to the planet earth at all times, not to each
point on the earth at all times. (it doesn't watch you just because you are
trying to catch a stereo portrait! ; -) The only difference between two
persons displaced by the DIA of the planet and one person who waits for the
planet to rotate the same distance is that of time. Since the moon will stay
in it's relative *face* position far longer than a single 12 hour period,
this process should provide a stereo shot with some degree of parallax.
Waiting for the natural wobble effect to be present would increase the
degree of parallax and provide a better stereo image.

Passengers aboard the Space Shuttle could get a wider stereo base and in
less time due to their orbit. Any optical satellite further out than the
Space Shuttle could capture stereo images from a much wider base. NASA
should have a library of stereo shots of the moon simply by combining
existing images which must have originated from varying orbital source
points. Other than finding one stereo star image at NASA, thanks to someone
here on P3D, I see no trace of other stereo images. If they exist they are
not cataloged as stereo in any traceable sense. (That I know of ...)

In practice, this technique done from earth faces the problems of
atmospheric distortion. These effects would force you to work with less than
a complete DIA. of the earth, so reducing the stereo base. If you could get
a stereo of that huge orange globe hanging just above the horizon, it would
be great except that atmospheric effects as well as light differences
between sunrise and sunset conditions would make it like using two different
lenses to take the picture. As the moon gets higher above the horizon, the
distortion becomes negligible, but the stereo base has been reduced. Any
astronauts on the list? ; -)

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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