IWCLIMTIOWr The angle between the earth's equatorial plane and 



the orbital plane of a satellite o The angle is measured at 



the ascending node, counterclockwise from the equatorial plane, 



looking toward the center of the earth. 

 NADIR: The point on the celestial sphere opposite the zenith, 



i.e., the point directly "below" a satellite, (see subsatellite 



point ) 

 NADIR ANGLE: The angle measured at the satellite between a given 



axis or ray and the local vertical. 

 PERIGEE: The point in an orbit nearest the center of the earth. 



(see apogee) 

 PROGRADE ORBIT: An orbit in which the satellite moves in the 



direction of earth rotation, (see retrograde orbit) 

 RESOLUTION: The ability of a film, lens, combination of both, or 



a vidicon system to render barely distinguishable a standard 



pattern of black and white lines „ 

 RKDROGRADE ORBIT: An orbit in which the satellite has a westward 



component of motion, i.e.., an orbit against the revolution of 



the earth, (see prograde orbit) 

 SUBSATELLITE POIM?: The point of intersection of the local 



vertical through the satellite with the earth's surface. 

 SIBI-SYISCHRONOUS ORBIT: An orbit such that the satellite maintains 



the same local sun time at each Equator crossing, (see 



geo-synchronous orbit) 



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