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With cylindrical tube length $l$ and diameter $d$, if the eye is
centered at one end of the tube, the half-angle of the field of view
is tan$(\theta) = d/2l$. The fraction of (sky viewed)/(whole sky) is
${{1}\over{2}} - {{{\rm cos}(\theta )}\over{2}}$. For the toilet paper
in our house, $l =$ 11.5 cm, and $d = $ 4.0 cm, yeilding $\theta =$
9.87 degrees, and a fraction of the sky covered of 0.0074. The
{\it correction factor} to translate your star counts to the whole sky
is the inverse of this fraction, or 135. You will want to confirm that
the tube you are using is the same size as mine before you just
blindly multiply by 135 to get the answer.


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\eject
\end
