334 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



procedures by which the precise reduction of film might be 

 accomplished. 



The objectives of this phase of the work were detailed as follows : 

 (1) to establish means of defining the film images that were measurable 

 and of locating them on the film when they were not apparent to the 

 naked eye; (2) to test the several machines available for the measuring 

 procedures; (3) to select and identify the reference stars in the back- 

 gromid; and (4) to estimate satellite magnitudes and variations in 

 brightness. 



Procedures were set up for filing and indexing all films received 

 from the Baker-Nunn camera stations and for sending to them pre- 

 liminary comments on the quality of the films themselves. Each film 

 was searched for satellite images not detected during field reduction. 

 For this purpose, film viewers and binocular microscopes were used. 

 With magnifications of 6.6 X and 20 X , a film could be scanned in two 

 sweeps, and then the microscope zeroed in on possible satellite images. 

 There was the suggestion that Mr. Nunn design a special blink-micro- 

 scope for detailed searching of the Baker-Nmm films; this was never 

 built, hovr'ever, because commercially available microscopes proved 

 wholly adequate to the job. 



Two sophisticated machines for measuring positions on the film 

 were chosen for test: the Mann two-screAv comparator, and the Van 

 Biesbroeck goniometer. Preliminary estimates suggested that the 

 former might be used on those films that, because of excellent images 

 and favorable distribution of reference stars, might produce the most 

 refined measurements, while the latter would provide sufficient accu- 

 racy for run-of-the-mill films. However, before any decision was 

 made, a detailed comparison of the two machines had to be undertaken. 



On the Van Biesbroeck photogoniometer the film is stretched to a 

 curvature similar to that at the focal surface of the Baker-Nunn 

 camera. The film is then positioned in a manner similar to that of the 

 strip in the Baker-Nmm camera itself. The plate takes the original 

 orientation with the use of known stars, and the measurer points a 

 microscope to the satellite image. The images are measured with a 

 precision goniometer placed in the center of the curved film. The 

 film holder is shifted toward the goniometer or away from it until 

 the angular distance of the selected stars (about 20 to 25 degrees 

 apart), as measured with the goniometer, satisfactorily approximates 

 tlie angular distance of these stars in the sky. Then the film holder 

 is moved in until the frame appears in the position in w^hich the film 

 was taken ; the horizontal plane corresponds to the celestial equator. 

 The differences in horizontal circular readings now equal the differences 

 in right ascension, and the differences in vertical circular readings 

 equal those in declination. 



