Pub 249, Volume 1: Sight Reduction for Air Navigation Selected Stars (EPOCH 2015)

PSP2491

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*** Discontinued, superseded by PSP2491-2020

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PUB 249, Volume 1: Sight Reduction for Air Navigation Selected Stars (EPOCH 2015)

The Sight Reduction Tables for Air Navigation consist of three volumes of comprehensive tables of altitude and azimuth designed for the rapid reduction of astronomical sights in the air. The present volume (Volume 1) contains tables for selected stars for all latitudes, calculated for the epoch of 2010.0, and replaces the previous edition calculated for the epoch of 2005.0; it is intended for use for about 5 years, when a new edition based on a later epoch will be issued. Volume 2 for latitudes 0°– 40° and Volume 3 for latitudes 39°– 89° are permanent tables for integral degrees of declination. They provide sights for bodies with declinations within 30° north or south of the equator, which includes the Sun, the Moon, the navigational planets and many of the navigational stars.

DESCRIPTION OF THE TABLES

These tables, designated as Volume 1 of the three-volume series of Pub. No. 249, Sight Reduction Tables for Air Navigation, contain values of the altitude (to the nearest minute) and the true azimuth (to the nearest degree) of seven selected stars for the complete ranges of latitude and hour angle of Aries. The arrangement provides, for any position and time, the best selection of seven of the stars available for observation and, for these seven stars, data for presetting before observation and for accurate reduction of the sights after observation.

In the calculation of the altitudes and azimuths the mean places of the stars for epoch 2010.0 have been used; corrections for precession and nutation are given in Table 5, but their omission will not give rise to a positional error greater than two miles in the years 2007–2012. No correction for refraction has been included in the tabulated altitudes, so that the full correction must be applied to the sextant altitudes.

Although Pub. No. 249 was designed for air navigation, it is also used extensively for marine navigation. The main differences in the use of Pub. No. 249 for marine navigation are highlighted at the end of this introduction. Volume 1 may be used without reference to an almanac such as The Air Almanac or The Nautical Almanac. The tables in this volume may be used with a clock, or other device, giving sidereal time.

USE OF THE TABLES

The tables are intended for use for two distinct operations—the planning of observations, and their reduction. It is important that full use should be made of the tables for the planning of observations. Planning of observations. Since only seven stars are given it is essential to refer to the tables before observation, in order to ensure that data will be available for the reduction of the observations.

This is done by estimating latitude and LHA ϒ for the proposed time of observation, from a knowledge of the DR position and GHA ϒ from Table 4 or an appropriate almanac, such as The Air Almanac or The Nautical Almanac. On reference to the tables this information gives immediately the seven stars available, together with their approximate altitudes and azimuths. From these seven stars, the observer can select those which best suit his particular purpose and the prevailing conditions; the approximate altitudes and azimuths make identification easy, and enable the sextant to be preset to the approximate altitude.

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