Davis Mark 3 Sextant User Manual

Mark 3 Sextant User’s Guide00011.220, Rev. EOctober 2008Total pages 20Trim to 5.5 x 8.Black ink onlyPage 1 (front cover)EDITED BY ROBERT B. KLEID© 200

Page 8FINDING LONGITUDEMeridians of longitude are measured east or west from the prime meridian (zerodegrees) at Greenwich, England. Because the groun

Page 9FINDING LATITUDEThe altitude of the sun at local noon may also be used to calculate latitude. First,the measured altitude must be corrected for

Page 10Presentations shown here are commonly used by navigators to help insure theaccuracy of their calculations:Figure 13 Figure 14Longitude Diagram(

THE ARTIFICIAL HORIZONAt times, it is not possible to see the natural horizon. Sun or moon shots may stillbe taken, with the aid of an artificial hori

Page 12THE SEXTANT AS A PELORUSYour sextant may also be used to find your position by sighting known landobjects such as lighthouses, small harbors, o

Page 13THE SEXTANT AS A HELIOGRAPHYou can use the sextant mirror to flash the sun’s rays several miles to attractattention, or to signal another perso

Page 14STUDENT NAVIGATION TABLESThe tables on the following pages give the approximate declination and equationof time of the sun. Latitude calculated

Page 15REFERENCE:Approximate Declination & Equation of Time

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Mark 3 Sextant User’s GuideProduct #011© 2008 Davis Instruments Corp. All rights reserved.00011.220, Rev. E October 2008INDEX SHADESHORIZONMIRRORIND

Includes everything you need: sextantuse and corrections, starfinder for 18stars, data entry form and step-by-stepsight reduction and plotting proce-d

Page 1HOW TO FIND YOUR POSITION WITH A SEXTANTThis booklet has been written as an introduction to your new Davis sextant. Bystudying its pages, you wi

Page 2MARK 3 SEXTANT ADJUSTMENTAdjusting your Mark 3 Sextant is easy and should be done each time it is used.All adjustments are made with the index m

Page 3Finally, remove the index error. Set the sextant at zero and look at the horizon.With the sextant still held to your eye, turn the screw that is

Page 4To measure the sun’s altitude, stand facing the sun with the sextant in your righthand. With your left hand on the index arm, look through the e

Page 5A nautical mile is equal to one minute of arc of a great circle. Since latitude ismeasured north or south from the equator, it is measured along

Page 6DECLINATIONEvery star and planet, including the sun, has a ground position, i.e., the spot onthe earth directly beneath it. Standing at the sun’

Page 7FINDING LOCAL NOON & THE SUN’S ALTITUDEAT MERIDIAN PASSAGEA meridian is an imaginary line drawn on the earth’s surface from pole to pole; al