with tracking of guided missiles and satellites. In addition, star photography 
must be considered an excellent means of calibrating precision photogrammetric 
cameras, because the method not only allows the determination of angular 
4) parameters, but the determination of the elements of interior orientation, 
ont'd including distortion coefficients, as well. (see chapter VI of this report). 
Whatever the purpose, the method relies simply on the fact that each 
celestial target point, known by its spherical coordinates, right ascension 
(a) and declination (8), provides an absolute control point situated at 
infinity. Thus, a direction in Space 1s fixed which is not sensitive to: 
changes in the position of the center of projection. Provided that the date 
£ and time of exposure, together with the geodetic ellipsoidal coordinates of 
the center of projection ( ÿ and \) are known, such a direction can be expressed 
with well-known formulas by a set of azimuth and elevation angles, or as more 
often used, by so called standard coordinates € and n, which are referred to a 
tangent plane on the unit sphere, described around the center of projection. 
With proper orientation, the t and n coordinates in the notation of this re- 
port, are equal to (X), (Y) with (2) = +1. (Compare formulas (12) ) 
d, ; The corresponding observational equations are formed exactly like those 
for absolute control points, with the exception that each of the partial 
differential coefficients associated with the AX Y A A parameter 
corrections becomes Zero, because of the celestial target points being at 
Lon infinity. 
" It is practical to incorporate the influence of astronomical refraction, 
(see chapter VII of this report) in the computation of the standard coordi- 
or. nates, so that for the corrected rays no further attention need be paid to the 
refraction problem during the triangulation computations. 
is Obviously, the sun also is such a celestial target and consequently, the 
ain aforementioned facts concerning the data reduction apply to it as well. The 
L use of the sun in aerial photogrammetry is important for strip and block 
triangulation, and appears to be mandatory for satellite photogrammetry, as 
well as for special attitude determinations of airborne photogrammetric 
cameras. The significance of celestial targets is not restricted to the fact 
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