[Tutor] [OT] Re: Floating Point Crazines

[Robert Sjoblom]

>> * Or you just get used to the fact that some numbers are not exact in
>> floating point.
>
> This got me thinking. How many decimal places do you need to
> accurately, say, aim a laser somewhere in a 180 degree arc accurately
> enough to hit a dime on the surface of the moon?
>
> Alan

In short: it's pretty much impossible. The mirrors used in the Lunar
Laser Ranging experiments are roughly the size of a suitcase (each).
Data from the APOLLO (Apache Point Observatory Lunar Laser-ranging
Operation) gives us some numbers to go by: it uses 1 gigawatt energy,
generating a (roughly) 1-inch long "bullet" of light. By the time it
hits the moon it will have distorted to a diameter of 1.25 miles
(earth's atmosphere is the biggest culprit). only about 1 in 30
*million* photons will actually hit the retroflector, and by the time
it gets back to the telescope on earth the beam is about 9 miles wide.
Again, only 1 in 30 million *of the returning* photons will hit the
telescope. Now imagine scaling the retroflector in size to a dime.

To bring it back on topic: could python handle these numbers reliably?
-- 
best regards,
Robert S.