10= 10" 10' 10!10s mi .01 .1 1 10 102 10" 10ยป 10s L.Y. Distance

Figure 42. Angular separation or size of objects as a function of distance from observer.

Some of these questions can not be answered definitively at present, but some approximate answers can be suggested. When viewing the universe through our atmosphere, it is difficult for us to observe a faint object when it is close to a much brighter object because the light from the brighter object interferes and because the degraded "seeing" through our atmosphere prevents the realization of the theoretical resolving power of large telescopes. A telescope employed in space, however, free from atmospheric effects, would be able to attain its theoretical resolving power for objects of equal brightness. Also, faint objects close to brighter ones might be observed through use of special techniques such as occulting

(hiding) the image of the brighter object with a knife edge. It has been indicated that this technique could be used if the two objects are separated by 2 seconds of arc or more (Roman, 1959). It will be assumed here, then, that a planetary object can be detected if it is separated by at least 2

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