THE_UMBRA
by Byron Soulsby
Isabella Plains
Lunar Observatory Australia

The atmosphere of the Earth is studied by observing its shadow on the
Moon - the Umbra.
Good agreement between the two data
sets was
obtained and
it has been conclusively shown that the umbra increases in size from
primary
contact to a value near the geocentric umbral semi-diameter.
The
image below illustrates a typical measurement of one image where the
umbral
semi-diameter (Fi) has
been measured with a
calibrated
image of the eclipsed Moon (red circle) with the best fit circle set to
coincide with the edge of the umbra. The value of Fi
was
0.646
o. The software used for measurement is Digimizer.

The measured umbra taken from a set of high quality images provided by Bernard Durand has enabled conclusive proof of my topocentric umbra theory and computation. For the first time these measurements have provided data points for the increase in the umbra size correlating closely to that computed.
It
has been conclusively shown that the observed umbra increases in size
from zero
at first contact rising rapidly to the expected ephemeris value.
I
believe this
is the first time the
characteristics
of the umbra have been adequately examined.
I
am indebted to Bernard Durand for the many excellent images provided
and for
his interest in this project.
The
web
pages
for the
Soulsby series of lunar eclipses.
My geometry
for the
computer
program for the determination of the topocentric umbral size.
Produced
by the Isabella Plains
Lunar Observatory
Australia, 20081002.