SIGHT REDUCTION TABLES FOR AIR NAVIGATION
Pub. No. 249 (HO-249) Volume 1 Selected Stars – Epoch 2025 - Commercial Edition
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. The way the 6 volumes of 229 were combined into this 3 volume set is this: volumes 2 & 3 cover all latitudes, but work only for declinations from 0° to 29° north or south. This covers the sun, moon, planets, and only those stars whose declinations fall into this range. Volume 1 contains some stars (whose declinations may be more than 29°) that are pre-selected for optimum viewing and direction. This volume is applicable for an 8 year period, centered on its Epoch date. The only drawback to this arrangement, is that it is possible that a star may be observed that is not one of the pre-selected ones, and whose declination is more than 29° north or south. This star, if observed on some unlikely occasion, say through a break in the overcast, could not be computed using the 249 tables. Nevertheless this remains the most popular tabular system in use.
Because of the high price and spotty availability of the Government editions, we have reprinted these as Commercial Editions from official Government electronic files or software. They are economical, and sized at 90% of the originals. They have soft instead of hard covers and their smaller size of 8.5 x 11 inches is easier to carry and store.
Volume I, used by both the marine and air navigator, contains altitude (to the nearest minutes) and true azimuth values of seven selected stars for the complete ranges of latitude and hour angle of Aries. These seven stars represent the best selection for observation at any given position and time, and provide the data for presetting instruments before observation and for sight reduction afterwards.
Volumes II and III cover latitudes 0°- 40° and 39°- 89° respectively and are primarily used by the air navigator in conjunction with observations of celestial bodies to calculate the geographic position of the observer.
Volume 1 – (Selected Stars) Epoch 2020
Volume 2 – Latitudes 0°- 40°, Declinations 0°- 29°
Volume 3 – Latitudes 39°- 89°, Declinations 0°- 29°
IMPA Code: 370738 (37 07 38)