THE LIMITS OF VISIBILITY OF A PARTIAL ECLIPSE OF THE SUN INFERRED FROM
OBSERVATIONS NEAR THE PARTIAL ECLIPSE LIMIT
By Francis Graham
The solar limb, when viewed through a telescope, either in projection of through a filter, exhibits undulation on its limb which is the result of atmospheric conditions in the Earth's atmosphere called "seeing". It is reasonable to assume that a minimal partial eclipse of the sun would be invisible as the lunar limb is deep within this zone of seeing irregularity.
The eclipse 1st contact was predicted to be , the maximum eclipse , and the last contact . The maximum magnitude was 0.005.
The actual time the eclipse was first visible was at . The eclipse was barely photographable (Fig. 2, taken at Maximum). The last the eclipse could be seen was 22:23:19, thus, it was visible only 9 min. 30 sec. This differs from its theoretical duration of 13 minutes 18 seconds, so there is the hint that the eclipse would not be visible at all if the duration were less than about 3 minutes.
William B. Hall viewed the Sun without a telescope, but with an aluminized mylar filter. No eclipse was visible, even at maximum.
reports from other locations in the tri-state area were examined. Gene
Henderson of Henderson Tool Company, near Emsworth, longitude 80o 4' 59"
latitude 40o 30' 29", who had a magnitude
of 0.002, photographically recorded the most faint hint of an eclipse. A
positive report was received by the Amateur Astronomers Association of
The theoretical northern limit for the partial phase was in McCandless Township, about 5 miles to the north of Allison Park, at 40o 33' 34" for longitude -80o 00' 00".
Thus the hypothesis that a partial phase of 3 minutes or less would be generally impossible to see seems to be verified. See map, Figure 3.
I thank my
colleagues W.B. Hall, G.A. Walsh and J. Weinhold for help, and George Guzik for
making reports to the Amateur Astronomers Association of
April 22, 2005