SECT. 3] 



APPLICATIONS OF THE GYROrENDULUM 



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observe in full daylight objects generally brighter than magnitude zero with 

 astronomical telescopes having apertures as small as 30 mm and to reach first 

 magnitude objects with apertures of about 50 mm. 



The brighter stars and planets (listed in Table I) can often be seen with 

 telescopic aid in daylight because the light of a point source or star can be con- 

 centrated optically by the ratio of the area of the entrance and exit pupils of 

 the telescope (when exit pupil equals the pupilary diameter of the eye), while 

 the brightness of an extended source, such as the background sky, is not in- 

 creased by optical means. Optical systems can, however, reduce the intensity of 

 background illumination to values considerably below the naked-eye level. 



Successful observation of stars in daylight involves physiological as well as 

 physical effects. Since the threshold of sensitivity of the human eye decreases 

 as the intensity of total stimulation rises, there are some advantages to be 



2 MILE RADIUS 



1 MILE RADIUS 



Fig. 8. Difference between 37 Geon and Loran fixes taken simultaneously from R.V. Chain 

 at sea. 



realized by placing the telescope in shaded observing conditions. It is also 

 found that elimination of the polarized component of scattered light can 

 heighten the apparent contrast of star images observed 90° or so from the sun. 

 Polaroid niters dim the stars nearly a full magnitude but under favorable 

 conditions, as when the air is free of large particles, they may enhance contrast 

 by reducing the background brightness of the sky an even greater amount. 



The apparent sharpness and contrast of a foveal image can be enhanced by 

 stimulating the surrounding portions of the retina — the phenomenon of spatial 

 induction. But if the extra-foveal illumination is too bright the contrast of 

 the foveal image is reduced. Thus a variable level of extra-foveal stimulation 

 could prove useful, or a very wide field eyepiece could be used so that the sky 

 itself might provide appropriate levels of extra-foveal stimulation through an 

 angle some 30 to 35° off axis. 



The principle of the navigational method has been shown to be sound but 

 there are numerous improvements possible in the optical and mechanical 



