Burdwood's Tables Second Edition (DAVIS. 2) - Sun's True Bearing or Azimuth Tables

Year: 1923 Language: english Author: Percy L. H. Davis Publisher: Imray, Laurie, Norie & Wilson, Ltd. Edition: Nautical tables Format: PDF Quality: eBook Pages count: 300 Description: For fifty years Burdwood's Tables have been known and used by every seaman, and the credit of originating Time Azimuth Tables is entirely due to their author, Captain John Burdwood, R.N. In recent times many uses for tabulated azimuths have been found other than the correction of the compass, for which they were first intended, and bearings are needed of bodies at greater altitudes than 6o°, which was the original limit. In respect of altitude, the present edition has no limit, azimuths being given from the meridian to the horizon—the latitude limit has been extended to 64 , and there are a few minor alterations which it is hoped will prove useful. As minutes of arc are useless in connection with azimuths, and as they tend to an incorrect idea of accuracy, they are replaced in this book by tenths of degrees, a change which makes for ease and accuracy in the interpolation that is sometimes necessary. The formula from which these tables were computed and the methods of their use are now so well known that no useful purpose can be served by recapitulating them, but it may be of use in dealing with the azimuth of the Moon or a star to remember that the hour-angle can be found by the following rule : — From the apparent time at ship (expressed astronomically—that is to say, reckoning from the preceding noon), get the apparent time at Greenwich, by applying the Longitude in (add if W., subtract if E.). With the date and time thus obtained, take out from the Nautical Almanac (page 1 for the month) the Sun's R.A. To this add the Apparent Time at ship, and from the sum, which is the R.A. of the Meridian, subtract the R.A. of the star. The remainder, if less than 12 hours, will be the star's Hour Angle W. of Meridian. If the remainder be more than 12 hours, take it from 24 hours, and the result will be Hour Angle E. of Meridian ; should the remainder be more than 24 hours, decrease it by 24 hours, and the result will be Hour Angle W. of Meridian. An arithmetical rule for the conversion of named azimuths into bearings on the o° to 360 clockwise compass, now printed on all charts, may be of service, thus : N. to E., no change. N. to W., subtract from 360 . S. to E., subtract from i8oc . S. to W., add to 180 . To these bearings all easterly deviations and variations are additive, and all westerly subtractive. Tables of the Sun's Declination and Equation of Time are included as before, and a star list in a shape very convenient for use is now added (see pp. 286, 287). The Author hopes that this book will be as welcome to sailors as its predecessor. PERCY L. H. DAVIS.

Contents

Burdwood's Tables Second Edition & Stars' Mean Places, 1923 in KINDLE, EPUB & PDF Formats.

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847^{®}29-Feb-2020 01:24## Burdwood's Tables Second Edition (DAVIS. 2) - Sun's True Bearing or Azimuth Tables

Language: english

Author: Percy L. H. Davis

Publisher: Imray, Laurie, Norie & Wilson, Ltd.

Edition: Nautical tables

Format: PDF

Quality: eBook

Pages count: 300

Description: For fifty years Burdwood's Tables have been known and used by every seaman, and the credit of originating Time Azimuth Tables is entirely due to their author, Captain John Burdwood, R.N.

In recent times many uses for tabulated azimuths have been found other than the correction of the compass, for which they were first intended, and bearings are needed of bodies at greater altitudes than 6o°, which was the original limit.

In respect of altitude, the present edition has no limit, azimuths being given from the meridian to the horizon—the latitude limit has been extended to 64 , and there are a few minor alterations which it is hoped will prove useful. As minutes of arc are useless in connection with azimuths, and as they tend to an incorrect idea of accuracy, they are replaced in this book by tenths of degrees, a change which makes for ease and accuracy in the interpolation that is sometimes necessary.

The formula from which these tables were computed and the methods of their use are now so well known that no useful purpose can be served by recapitulating them, but it may be of use in dealing with the azimuth of the Moon or a star to remember that the hour-angle can be found by the following rule :

—

From the apparent time at ship (expressed astronomically—that is to say, reckoning from the preceding noon), get the apparent time at Greenwich, by applying the Longitude in (add if W., subtract if E.).

With the date and time thus obtained, take out from the Nautical Almanac (page 1 for the month) the Sun's R.A.

To this add the Apparent Time at ship, and from the sum, which is the R.A. of the Meridian, subtract the R.A. of the star. The remainder, if less

than 12 hours, will be the star's Hour Angle W. of Meridian.

If the remainder be more than 12 hours, take it from 24 hours, and the result will be Hour Angle E. of Meridian ; should the remainder be more than 24 hours, decrease it by 24 hours, and the result will be Hour Angle W. of Meridian.

An arithmetical rule for the conversion of named azimuths into bearings on the o° to 360 clockwise compass, now printed on all charts, may be of service, thus :

N. to E., no change.

N. to W., subtract from 360 .

S. to E., subtract from i8oc

.

S. to W., add to 180 .

To these bearings all easterly deviations and variations are additive, and all westerly subtractive.

Tables of the Sun's Declination and Equation of Time are included as before, and a star list in a shape very convenient for use is now added (see pp. 286, 287).

The Author hopes that this book will be as welcome to sailors as its predecessor.

PERCY L. H. DAVIS.

## Contents

Burdwood's Tables Second Edition & Stars' Mean Places, 1923 in KINDLE, EPUB & PDF Formats.## Screenshots