Re: Just to be sure: Planet with multiple moons

Mike Williams <nospam@[EMAIL PROTECTED]
> wrote:
> Wasn't it Phillip Thorne who wrote:
> 
>>The rest of the time, there's a dramatic closeup in which a character
>>is standing on the roof of a skyscraper, silhouetted against a full
>>moon that covers about 20 degrees of arc.  I don't think there are any
>>lenses that can do that...
> 
> I've seen the effect done for real in wildlife TV programs. The sort of 
> lenses that they use for getting close-ups of wildlife from considerable

> distances away will make the Moon do much more than fill the screen.
> 
> And, for example, these are claimed to be real photos taken through 
> telescopes:
> <http://www.spacew.com/gallery/image003746.jpg>
>
<http://www.interfaithmarianpilgrimages.com/media/images/moonrise_cross2.
> jpg>

A simple thought experiment should reveal that it's possible to make the 
moon look vastly larger.

As your subject, choose a round rock with a clear view behind it. Place 
your camera so that it forms a straight line with the subject rock and a 
slightly larger rock resting on the moon's surface.

Now, assume that your camera has unlimited zoom and resolving power. At 
the start you are close, and the moon is small compared to the rock. Back 
away, increasing the zoom to keep the rock's apparent size constant. The 
moon will grow in apparent size in the picture. At the limit, as you back 
away to infinity, the rock on the moon will eventually become visible 
behind the rock on the Earth, as it is slightly larger. At this point the 
moon itself will be mostly invisible because it will be vastly larger than

the frame of your photograph, and you'll see your Earth rock and a tiny 
portion of the moon's surface behind it.

More realistically, higher zoom levels will tend to compress the apparent 
distance between near and far objects and make distant objects appear 
larger relative to near objects. You can make the moon look insignificant 
by getting very close to the subject and using very low zoom, or you can 
make it loom over your subject by standing a good distance away and using 
high zoom. There's nothing necessarily unrealistic about such a picture, 
although it's possible that the size and position of other elements in it 
would be incompatible and give away the game.

-- 
Michael Ash
Rogue Amoeba Software