V Scan the text to fill in the gaps in each sentence with the prepositions.1 Human navigators use sextants ___ measure the elevation angle of celestial bodies ___ the visible horizon. 2 The peak elevation angle occurs ___ local noon or midnight:elevation angle (degrees) = 90 –latitude + declination. 3 Thus, ___ local noon or midnight, latitude can be calculated ___simple arithmetic ___ a table of declination (the angle of the sun or star ___ the Earth’s equatorial plane). 4 When time began to be broadcast ___ vehicles ___ the 1930s, off-meridian observations of the elevation angles of two or more celestial bodies became possible ___ any known time of night (cloud cover permitting). 5 These fixes were hand-calculated using logarithms, then plotted ___ charts ___ a navigator. 6 ___ the 1930s, hand-held bubble-level sextants were built to measure the elevation of celestial bodies ___ an aircraft without the need to see the horizon. 7 The human navigator observed sun and stars through an astrodome ___ top of the aircraft. 8 The accuracy of celestial fixes was 5–50 miles ___ the air, limited ___ the uncertainty ___ the horizon and the inability to make precise angular measurements ___ a pitching, rolling vehicle. 9Kayton reviews the history of celestial navigation ___ sea and ___ the air. 10 The first automatic star trackers, built ___ the late 1950s, measured the azimuth and elevation angles of stars relative ___ a gyroscopically stabilized platform. 11Approximate position measurements ___ dead reckoning allow the telescope to point within a fraction of a degree of the desired star. 12Thus, a narrow field-of-view is possible, permitting the telescope and photo detector to track stars ___ the daytime through a window ___ top of the aircraft. 13 Automatic star trackers, used ___ long-range military 18-10 aircraft and ___ Space Shuttles, are physically mounted ___ the stable element of a gimballed inertial navigator. 14 Future lower-cost systems may mount the star tracker directly ___ the vehicle.
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