Re: free fall data

[brian whatcott <inet@intellisys.net>]

At 09:15 9/16/97 EDT, you wrote:
> > ... A prime method to REDUCE parallax errors 
> > is to place a camera at as large a distance as possible and use the 
> > largest magnification which a telephoto lens can offer - i.e. by zooming.
> > Visualize the extreme rays from the target, and the angle which they
> > subtend at the camera; furthest distance = smallest angle.
>
> This is a very important piece of information. I can not visualize the
> rays. Can you give us a reference, Brian?  
>                                             Thanks.

A science dictionary offers this for parallax:
The difference in direction, or shift in the apparent position, of a body
due to a change in position of the observer.

 Astronomers took to using as a unit of distance the parsec which
represents a distance of about 3.26 ly. It is the half angle of one second
between celestial sightings six months apart on a baseline provided by the
Earth's orbital diameter.
In this context, placing the Earth's orbital baseline further from
a star of interest implies a reduction in the angular difference of
sightings over the semiannual baseline - i.e. a reduction in parallax.

A very readable account of this and many other topics for young people was
selected by Tim Ferris (Prof. Astronomy, UCalBerkeley) for the 'Book of the
Month' title, "World Treasury of Physics, Astronomy & Maths" Little, Brown
& Co, 1991.
 Harlow Shapley's contribution includes this;
"When you hold your finger near your eye, the displacement is large [if
your head moves...] - the parallax is large, I might say - and if the
finger is held as far as possible from your face, the shift is much smaller.
"The smaller the shift, that is, the smaller the parallax of your finger,
the more remote it is."




brian whatcott <inet@intellisys.net>
Altus OK