RE: Diverging Light Rays

2000-02-15 Thread Andrew James 

Tony Moss suggested using a non-diverging sunray after passing between pairs
of posts 0.4mm apart for a heliochronometer.  

Art Carlson wrote: snip But this line is not unique.  You will get such
a line if the instrument is aligned toward any part of the sun's disk.
end

My idea is this: is it possible to combine the two points made?  Arrange,
say, two sets each of four posts with three 0.4 mm gaps between, one set
having slightly wider posts but with the same gap, so as to make three light
rays the outer two of which diverge by the same small amount - say 0.2
degrees - in each direction from the inner.  Then balancing the appearance
of the outer rays should give a rather more accurate estimation of the angle
of the centre of the solar disc.Any takers?

Regards
Andrew James

Re: Diverging Light Rays

2000-02-15 Thread Arthur Carlson 

Andrew James [EMAIL PROTECTED] writes:

 My idea is this: is it possible to combine the two points made?  Arrange,
 say, two sets each of four posts with three 0.4 mm gaps between, one set
 having slightly wider posts but with the same gap, so as to make three light
 rays the outer two of which diverge by the same small amount - say 0.2
 degrees - in each direction from the inner.  Then balancing the appearance
 of the outer rays should give a rather more accurate estimation of the angle
 of the centre of the solar disc.Any takers?

I'll buy it.  I did a lot of thinking and some experimentation last
summer.  I used a slit and two pinholes and tried to balance the
intensity of light on the two sides.  I found I could judge the moment
of symmetry within a second or two of time, which corresponds to one
arc minute or better of angle, which I found very respectable.  The
principles are these: (1) your eye can judge symmetry better than just
about anything else, and (2) the light passing through
lenses/pinholes/slits varies most sensitively if the apparatus is
aligned with the limb of the sun.  My slit produced a line image of
the sun.  Both the diameter and the separation of my pinholes were
about equal to the width of this line image.

--Art

RE: Diverging Light Rays

2000-02-15 Thread Tony Moss 

Andrew James cxontributed:

My idea is this: is it possible to combine the two points made?  Arrange,
say, two sets each of four posts with three 0.4 mm gaps between, one set
having slightly wider posts but with the same gap, so as to make three light
rays the outer two of which diverge by the same small amount - say 0.2
degrees - in each direction from the inner.  Then balancing the appearance
of the outer rays should give a rather more accurate estimation of the angle
of the centre of the solar disc.Any takers?

What a CLEVER notion!  I'll make an experimental model when time permits

Best Wishes

Tony M.

P.S.  I can't recall if I mentioned the reason for the 0.4mm gap.  For 
just a simple sunray a finer gap between cylindrical posts would be OK 
BUT my meridian layout device also serves as a two-way 'sight' and a 
smaller gap makes spotting even a 'dayglo' pole at a distance quite 
difficult.