Long Term Almanac 2000-2050: For the Sun and Selected Stars With Concise Sight Reduction Tables, 2nd Edition - Softcover

Kolbe, Geoffrey

Softcover

ISBN 10: 0914025104 ISBN 13: 9780914025108

Publisher: Starpath Publications, 2008

Synopsis

Arrangement

The main body of the Almanac consists of ephemerides from which the Greenwich Hour Angle (GHA) of the sun, the declination of the sun and the GHA of Aries may be determined for any time from the year 2000 to 2050. These are based on the fact that approximately correct values for the position of the sun and the GHA of Aries may be obtained from an almanac that is exactly four years out of date. By applying quadrennial correction factors, an ephemeris for any given year may be used to determine the position of the sun and the GHA of Aries to good accuracy exactly four years hence and multiples thereof.

The Daily tables for the four years 2000 to 2003 inclusive give the 00 hrs value for the GHA of the sun, the declination of the sun and the GHA of Aries. Quadrennial correction factors are also given so that positions for the sun may be determined for any subsequent year until 2050. Also tabulated are averages for the hourly rates of change for the sun's declination and the hourly acceleration of the sun's GHA for that day. A separate Tables of GHA increments allows the increment for any given time of day to be added to the GHA value from the Daily tables, so giving the sun's GHA for any time.

The period of validity for these tables has been set at fifty years, that being the period for which simple, linear, quadrennial correction factors for the sun will still give good accuracy for corrected table values. (In fact, good accuracy should be maintained until 2060, but accuracy will deteriorate rapidly thereafter.)

The GHA of Aries may be determined for any given time and date until the year 2060, using the Daily tables and the Tables of GHA increments.

Tables for the positions of 39 selected navigational stars, including Polaris, are given for the year 2000. Annual correction factors are also given to account for their subsequent apparent motion, so that their positions may be calculated for any subsequent year.

Star charts showing the positions of the selected stars are given. These stars are also shown in the context of prominent constellations and other stars.

Formulae are given for sight reduction using a calculator.

Finally, concise tables for sight reduction are given. The tables given here are a version of the "NAO Sight Reduction Tables" as used in the Nautical Almanac since 1989. The tables were originally created by Admiral Davies, founder of the Navigation Foundation, in collaboration with Dr. Paul Janiczek, former Head of the Astronomical Applications Department of the US Naval Observatory. Admiral Davies donated his work on the project to the Nautical Almanac Office in the name of the Navigation Foundation for the benefit of all mariners. An earlier form of the tables, called the Davies Concise Tables, was published by Cornell Maritime Press.

Data sources

The Nautical Almanacs for the years 1996 to 1999, published by HMSO, were used as a starting base for the ephemerides given in the Daily tables. Quadrennial corrections for the sun and annual corrections for the selected stars were determined using the Stormy Weather Astro program, written by Paul Adamthwaite of Stormy Weather Ltd., Picton, Ontario, Canada. This program uses algorithms based on the recent resolutions of the International Astronomical Union, the new standard epoch J2000.0, the FKS system and the new orbital data from the Bureau des Longitudes in Paris, France.

Accuracy

For the earlier years during which these tables are valid, the error of the values for the GHA and declination of the sun as tabulated in the Daily tables and corrected using the quadrennial correction should be of the order of 0.25'. In one percent of cases the error will be about 0.5' but the error should never exceed 0.7'. The GHA of Aries as tabulated and as corrected using a constant quadrennial correction factor of 1.84' should generally not be in error by more than 0.3'

However, during the later years for which these tables are valid, uncertainty in the future behaviour of delta T will start to dominate over other potential error sources. By 2050, this uncertainly will contribute errors in the GHA of the sun and Aries of about ±1', (but it could be as much as ±2.5'). See the section on Time below.

The Sidereal Hour Angle (SHA) and declination of the stars as tabulated should generally not be in error by more than 0.3' up until the year 2050. The SHA of the selected stars are given for the 15th of each month. A slight increase in accuracy may be achieved using interpolation to achieve the value for the day in question.

The calculated altitude derived using the Sight reduction tables will have a precision of 1' and in general the accuracy should also be 1'. The azimuth is calculated to a precision of 0.1°. The tables should not be used for latitudes higher than 80°.

About this title

From the Author:

Today, celestial navigation is mainly used by the recreational sailing community. Even then, it is not usually used as the principal means of determining a position, but either as an emergency backup in case of malfunction in the electronic navigation, or for the pleasure of learning and practicing an ancient art. Either way, the use of celestial navigation is occasional and infrequent and so a long term almanac which does not need updating every year becomes attractive.

The aim has been to produce an almanac of small size, is practically useful in keeping oneself found using celestial navigation and which will remain valid for a period of 50 years. Ease of use has been a prime consideration in the design of this almanac, the layout of which is modeled on that of the Nautical Almanac to give the Long Term Almanac a familiar look. Explanations are detailed and numerous examples are given. However, a working knowledge of celestial navigation is assumed.

About the Author:

Born and brought up in the city port of Southampton, England, the author's father was a sea captain. However, an interest in celestial navigation was not awakened until Geoffrey Kolbe had defended a Ph.D. in physics at Imperial College, London, and was working in California at Lawrence Livermore National Laboratory.

Even then, Kolbe had no real interest in sailing, (one bit of the ocean looks much like another), but was interested in the use of celestial navigation for staying found on land, particularly in desert landscapes - which are oceans of another sort. Using aircraft sextants and a theodolite, Kolbe has practiced the "old methods" to keep track of position on three trips to the deep Sahara desert, a thousand kilometres from the nearest black topped road.

About this edition

• Publisher: Starpath Publications
• Publication date: 2008
• ISBN 10: 0914025104
• ISBN 13: 9780914025108
• Binding: Paperback
• Number of pages: 120