Project Blue Book Special Report (second copy)

This information consisted of:
(1) Time and date of observation in Greenwich Civil Time
(2) Latitude and longitude of the observer at the time of
observation.
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Figure 39 shows a celestial sphere on which 2J_ represents the ob-
server1 s zenith, js represents the sun, and N_ represents the north celestial
pole.
Using the date and time of the observation, the longitude and declina-
tion (S) of the sun were obtained from an ephemeris of the sun and corrected
for the equation of time. The difference between the longitudes of the sun
and the observer was taken, and.called the hour angle (HA on Figure 39).
Then, using the declination of the sun (S_), the latitude of the observer
(lat), and the hour angle (HA), the angle (ZS) between the observer' s zenith
and the sun can be calculated from the law of cosines of spherical trigo-
nometry. Thus, cos Z"S = cos (90 - lat) cos (90 - S) + sin (90 - lat) sin
(90 - S) cos (HA).
Since the angle ZS is measured from the observer's zenith, the angle
of elevation of the sun above the horizon for daytime sightings was found by
taking 90 - ZS. When the sun was below the horizon, the angle of depres-
sion of the sun below the horizon was found by taking ZS - 90..
Having found the angle ZS, the bearing of the sun (angle B) was ob-
tained from the formula:
sin (B) _ sin (HA)
sin (90 - S) = sin (ZS)
All of the above calculations were made with IBM equipment. Sines,
cosines, and^heir inverses were obtained from a deck of 9,000 IBM cards
on which seven-place Peter1 s tables of the sines, cosines, and tangents of
angles had been punched for each 0.01 of a degree from 0 to 90 degrees.
Upon completion of these calculations, the cards representing OBJECT
SIGHTINGS were sorted on the sign of the sine of the bearing angle. This
separated the cards into two groups: (1) sightings which occurred between
noon and midnight, for which the sine of the bearing angle was positive; and
(2) sightings between midnight and noon, for which the sine of the bearing
angle was negative. Then each of these groups was sorted into groups for
intervals of 10° in angle of elevation of the sun from -90° to +90°. A count
was made of the number of cards in each group and from this a histogram
was constructed (Figure 40). The UNKNOWN OBJECT SIGHTINGS were
then sorted out, counted in the same manner, and a histogram was made
(again see Figure 40).
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