Celestial Precomputation

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Celestial precomputation methods have been brought to the forefront with the proliferation of high-speed aircraft. Aircraft speeds make it necessary to minimize the time between shooting and fixing. Since the sextant may be the only means of viewing the body, it is necessary to precompute the altitude and azimuth of a body in order to locate it. Remember corrections may be applied to the Hc, Ho, or intercept, and pay close attention to the sign of the correction. In addition to precomputation, the fix may be resolved faster by preplotting the true azimuths of the bodies.

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Recommended Tools

Rotating Flight Navigation Plotter – Rotating azimuth eases flight planning with direct course readout. 8 scales to meet the needs of all VFR aeronautical charts; nautical on one side, statute on the flip. Nautical-statute conversion scale also included.

Slide-Rule-Style E6B Flight Computer. On the circular side, black is used for the rate arrow and units to be calculated; Red is used for weight and volume; Blue is used for distance, time and temperature scales. On the wind side, colors are used to identify wind variation: blue identifies west (or right wind correction angle) and red identifies east (or left wind correction angle). ASA’s color E6-B is made with solid aluminum construction and features the functionality pilots have relied on for decades.

Additional Navigation Tools and Resources

  • U. S. Air Almanac 2018 – The Air Almanac 2018 contains the astronomical data required for air celestial navigation, making it a necessary resource for all pilots and others attempting to chart routes based on celestial bodies. The Almanac also provides the Greenwich hour angle and declination of the Sun, Moon, and three navigational planets along with the Greenwich hour angle of Aries, all tabulated at 10-minute intervals.
  • Davis Instruments Sextant – Used for measuring the angular distances between objects and especially for taking altitudes in navigation.
  • Sight Reduction Tables For Air Navigation Pub. No. 249 – Vol 1.  – These tables were designed for air navigation where weight and space are at a premium, however, they are very popular with sailors too due to the fact that Vol. 1 offers a speedier way to compute stars.  Volumes two and three may also be helpful.