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On Wed, 04 Jun 2008 21:04:39 -0600, Gary J. LaPook   
wrote:

> Back on November 4th, 2007 we were discussing the Bumstead sun compass.
> I just recently visited the Smithsonian Air and Space Museum Udvar-Hazy
> Center at Dulles airport and they have one on display and I have
> attached a photo of it.

Thank you; differs from other images I've found.

While on the subject of Sun Compasses: I wonder if you've studied the D.  
H. Baldwin Solar Chart, as used by the US Geological Survey for orienting  
their plane tables?

I have a "Revised edition 1922".  It is basically a series of ellipses  
covering 33� to 70� latitude, with the long axes from 90� to 270� then cut  
in half at 0� to 180� (Local Apparent Noon).  Follow the inset diagrams  
for the graphical solution of the equation of time, transfer to a pivot  
point graph, and mark a point on the declination base line.  Correct watch  
time for longitude difference from a standard time meridian and plot a  
point on the correct latitude ellipse.  Line up a shadow (cast by a  
vertical object with the chart on a level board) from the local apparent  
time point on the ellipse to the equation of time point on the base; and  
the base line will be pointing to astronomical N or S.

There is a quarter day correction of the equation of time for each year,  
starting at 1922 and going to 1952 "etc.", on a four year cycle.  The  
chart says to advance an additional quarter day after 1940.

My question is:  What happens in the year 2000?  Is there enough of a  
difference in the declination of the sun to require an additional advance  
by 2008?

-- 
Richard . . .

Using Opera 9.2.4 after the "Dog" died

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