Presentation on theme: "Junior Navigation Chapter 1"— Presentation transcript:
1Junior Navigation Chapter 1 Hostile Vessel Operating in this areaLighthouses in the SkyNE5Junior NavigationChapter 1
2Learning ObjectivesDefine terms: altitude, circle of position, geographical position, intercept, and celestial line of position.Given altitude, determine the radius of a circle of position and vice versa.State why accurate time is important in celestial navigation.Describe the altitude-intercept method of plotting a celestial line of position.
3When body is at your zenith: Latitude = Dec and Longitude = GHA Apparent BodyBodySDULLLGHA & DecTermsDecAstronomical RefractionCelestial EquatorCelestial SphereWhen body is at your zenith: Latitude = Dec and Longitude = GHAApparent Line of SightParallaxhshaZenithindex correction (IC)Observer’s EyeheSensible HorizondipHo (Altitude)Geoidal HorizonDRNSGPLatitudeCOPCelestial HorizonVisible HorizonEquatorEquatorLongitudeTerrestrial RefractionGeometrical Horizon3Nadir3
4Law of Cosines(cos LHA x cos Lat x cos Dec) + (sin Lat x sin Dec) = sin Hcconvert sin Hc to Hc (calculated sextant height)Difference between Hc and Ho provides distance fromyour DR to COP.[sin Dec – (sin Lat x sin Hc)] / (cos Lat x cos Hc) = cos Zconvert cos Z to Zn provides direction (azimuth) to GP.44
5The Fundamental IdeaIn AP, a Radar Fix was determined by plotting two LOPs taken from radar.
6Plotting a Circle of Position You need to know:Direction from observer to the GP of the body; andDistance from observer to the GP of the body; but first –You need to know how to convert altitude difference to nautical miles.
7Angular DistanceRadius of a circle of position is equal to 90° minus the altitude (1º latitude = 60nm).90º – 90º = 0º 0º x 60nm = 0nm90º – 0º = 90º º x 60nm = 5400nm90º – 30º = 60º º x 60nm = 3600nm?
8COP and AltitudeAt 1034 an observer in Galveston measures the sun’s altitude to be 77°41.5´. What is the radius of the COP?90°00.0´–77°41.5´12°18.5´12° x 60 nm/degree = nm18.5´ x 1 nm/minute = nmTotal = nm (radius of COP)
9COP and AltitudeAt the same time observer in Los Angeles measures the sun’s altitude to be 57°34.1´. What is the radius of the COP?90°00.0´–57°34.1´32°25.9´32° x 60 nm/degree = nm25.9´ x 1 nm/minute = nmTotal = nm (radius of COP)99
10Altitude-Intercept Method At a sight of the sun is taken. Recorded altitude = 57°34.1’ COP 1,945.9nm10341000
11Altitude-Intercept Method Calculate true bearing (azimuth) and altitude (Hc) from DR using Law of Cosinesto GPZn103410001111
12Altitude-Intercept Method Difference between Ho (observed altitude) and Hc (calculated altitude) is the interceptHo 57º 34.1’Hc 57º 24.1’Diff ’ towardsIntercept 10.0nm103410nmWhen Hc is greater than Ho, your azimuth is the reciprocal of computed azimuth.1000COP drawn as a straight line perpendicular to the azimuth1212
13Altitude-Intercept Method Label with time of sight and name of body10341034 Sun10001313
14Altitude-Intercept Method When you have only a single LOP, you obtain an estimated position (EP)10341034 Sun10001414
15Quiz1. If two observers at different DR positions measure the altitude of the same celestial body at the same time,a. the observer closer to the GP of the body measures the larger altitude.b. the observer closer to the GP of the body measures the smaller altitude.c. both observers measure the same altitude.d. the positions of the observers relative to the GP cannot be determined because the azimuths from each observer are not given.
16Quiz2. Polaris (the North Star) is located exactly over the earth's north geographic pole.a. Trueb. False1616
17Quiz3. The vertical angle measured with a sextant between a celestial body and the horizon is called:a. azimuth.b. intercept.c. altitude.d. zenith.1717
18Quiz4. A navigator determines the altitude of the sun to be 37°26.1'. What is the distance in nautical miles between the navigator's position and the GP of Sun?Solution:90 ° - 37°26.1´ = 52° 33.9´52° x 60nm/° = nm+ 33.9' x 1nm/' = nm3,153.9nm1818
19Quiz5. The difference between the calculated altitude (Hc) and the observed altitude (Ho) is called:a. azimuth.b. co-altitude.c. altitude.d. intercept.1919
20Quiz6. The method used in plotting a celestial LOP is called “the altitude-intercept method”.a. Trueb. False2020
21Quiz7. The geographical position (GP) of a body is defined as the point on the surface of the earth directly beneath the center of the body.a. Trueb. False2121
22End ofLighthouses in the SkyThe SextantJunior NavigationChapter 2
23Learning ObjectivesIdentify the parts of a sextant and understand how a sextant worksDetermine index error & index correctionDescribe how to handle, maintain & stow a sextantDescribe techniques for taking Sun sightsDescribe safety procedures for taking sights on a boatRecord the time of a sightIdentify the ideal & practical accuracy limitsIdentify erroneous sights in a run of sightsDescribe the sight requirements for JN2323
24Parts of the Sextant ? Sight Tube 2X or 4X Telescope Handle Lanyard FrameLimbIndex Arm?Release ClampArc (degrees)Micrometer (min)WholeSplitHorizonVernier (tenths)Horizon GlassIndex MirrorHorizon ShadesIndex ShadesTelescope2424
25How a Sextant Works The sextant set to 0°00.0´ The horizon will appear as an unbroken line when the sextant is correctly adjustedSplit FieldFull Field2525
26How a Sextant Works Telescope aimed at the horizon Index arm adjusted to the appropriate angleSplit FieldFull Field2626
27Reading a Sextant Accurate reading is necessary 0.1’ of arc equals 0.1 nmFull turn of micro drummoves index arm one degreeVernier - auxiliary scale to interpolate the minute scale of micrometer drum2727
28Reading the Measured Angle First read degrees from the arcThen read minutesfrom micrometer drumFinally read tenths of minutesfrom vernier2828
29Reading a Measurement Read the Drum Read the Arc Read the Vernier Index Mark40°02.6’40°02’40°2929
31THIS INSTRUMENT IS FREE OF ERRORS FOR PRACTICAL USE Sextant ErrorNon-adjustable errorAdjustable errorTelescope axis - not parallel to frameIndex mirror - not perpendicular to frameHorizon glass - not perpendicular to frameIndex mirror and horizon glass are not parallel when sextant set to 0°00.0´Checking & adjustment procedures in BowditchShould only be made by experienced personsFrequent adjustment might loosen screwsASTRA IIIBTHIS INSTRUMENT IS FREE OF ERRORS FOR PRACTICAL USE3131
32Index Error (IE) IE is common In good quality metal sextants IE tends to remain fairly constantIn plastic sextantsChecking IE critical3232
33Determining Index Error (IE) Set sextant to 0°00.0´ and sight on horizonIf 2 images of horizon not superimposed ORIf horizon shows as broken lineIE present3333
34Determining Index Error (IE) To determine value of IE.Adjust micro until horizon appears as straight line.IE is the sextant reading:If index mark is below 0°00.0´ is off the arcIf index mark is above 0°00.0´ is on the arcFull FieldSplit FieldOFF THE ARCON THE ARC3434
35Index Correction (IC)IC - value applied to the altitude measured to correct for IEIC - always opposite to the sign of IEIE ‘on the arc’ requires negative ICWhen it’s on, take it offIE ‘off the arc’ requires positive ICWhen it’s off, put it onON THE ARCOFF THE ARC3535
36Index ErrorWhen the horizon line is continuous, the index mark is between 0° and +1° and the micrometer/ vernier reads 4.5´The sextant altitude (hs) is 34°23.6´5101548On or Off the Arc?What is the IE?What is the IC?What is ‘ha’?ON the Arc+ 4.5’– 4.5’34º 19.1’when it’s on take it off3636
37Index ErrorWhen the horizon line is continuous, the index mark is between 0° and –1° and the micrometer/ vernier reads 56.3´The sextant altitude (hs) is 34°23.6´555485010On or Off the Arc?What is the IE?What is the IC?What is ‘ha’?OFF the Arc– 3.7’+ 3.7’34º 27.3’when it’s off put it on3737
38Caring/Cleaning for a Sextant Delicate precision instrumentsHandle sextant by grasping its frame or handle - never by its limb, index arm, or telescopeAvoid touching mirrors except to clean themSet sextant down on its legs - never mirror sideNever put sextant where it can fallStow sextant in its case in a secure spotClean mirrors with lens paper or soft lint-free clothRemove salt spray with fresh waterLubricate with light coat of fine instrument oil3838
39Sight-taking Supplies Sextant (obviously)Watch with second handNotebook/pencil – record sight dataChart of the areaTape measureTHENFamiliarize yourself with your sextantPractice taking sights at a beach or pierNatural horizon vs. dip short of the horizonWhen comfortable, take sights from a boat3939
40Bring Down the Sun Set sextant to 00°00.0´ Move all horizon shades into positionAim it up at the sunSweep sky to find sunIf sun not visible, remove shades, one at a timeWhen visible, select index shades of same density4040
41Bring Down the Sun When the Sun is caught Release and slowly move index arm forward while rotating sextant downwardKeep sun in view in telescope constantlyContinue until you are near the horizonAdjust horizon shades, if neededSun also seen near horizon4141
42Bring Down the Sun When sun’s image near horizon Release clamp to reengage tangent screwBring sun to appear on the horizon, then4242
44Recording Sextant Altitude Call out “Stand by” to RecorderRecorder responds “Ready”Adjust micrometer drum to place sun on horizonWhen sun on horizon, call “Mark”Recorder notes time:Seconds, minutes, hour – in that orderRead angle from sextant for RecorderRepeat steps for a run of sights4444
45Alternate Method To take sights at predetermined intervals Call out “Stand by” to RecorderRecorder responds “Ready in xx seconds” and begins countdownDuring countdown, adjust micrometer drum to keep sun on horizonRecorder calls “Mark” when countdown completeRecorder notes time:Seconds, minutes, hour – in that orderRead angle from sextant for Recorder4545
46Taking Sights at SeaTaking sights at sea can be difficult, sometimes dangerousUse a safety harnessTechniques: Hit and Run; Wait and See4646
47Special Techniques Dip short of the horizon Acceptable for JN sights Back sightArtificial horizonNot acceptable for JN sightsOK for practice sightsSee Appendix A for details4747
48Accuracy of Sights Modern marine sextant - readable to 0.1´ Nautical Almanac data are given to 0.1´Sights timed to nearest secondError of 1 second in time lead to error of 0.25´ of arcPractical Accuracy limited by:Skill of ObserverQuality of SextantStability of observing platformVisibility & Atmospheric ConditionsPractice – Practice – Practice4848
49Runs of Sights Taking several sights on a body improves accuracy Corresponding altitude changes should be proportionately constantPositive direction for rising bodiesNegative direction for setting bodies4949
50Run of Sights Time Difference Altitude 14-16-43 38°06.2’ 58s –10.4´ 37°55.8’–10.1´56s37°45.7’55s+5.1´37°50.8’58s–25.2´37°25.6’5050
52JN Sight Requirements Two Sun sights simulating RFix One upper and one lower limb sightAcceptable accuracy of all sights is 5nmQualified ‘run’ of sightsSights with altitude greater than 75° are discouragedRecording your sightsUSPS Sight Log FormSight Folder must be completed before you can take examDetails in Appendix D5252
53JN Sight Requirements Arthur Mollica Art Mollica (E066699)St Paul1 of 1JN Sight Requirements2012Sun LOP, KP by GPS, DST, D1.3m fm chart129 JunSun LL0-00+635º 45.4’EDs8.5-0.344º 29.9’N92º 18.7’W2““““35º 51.4’“““““““336º 02.8’436º 14.2’536º 24.8’Sun LOP, KP by GPS, DST, D180yd fm chart629 JunSun UL0-00+647º 00.8’WDs8.5-.0344º 29.9’N92º 18.7’W746º 55.8’846º 49.4’8““““46º 42.6’“““““““846º 38.4’Arthur MollicaSight Folder will also contain USPS SIGHT REDUCTION FORM (SR96a) for each of the selected sights and a USPS CLSSAPS (Form CLS86) plotting the resulting RFix of these selected sights.5353
54Quiz1. When reading sextant altitude, in what order are degrees, minutes, and tenths of minutes read?DegreesMinutesTenth of Minutes1st2nd3rd
55Quiz2. When timing sights, in what order are hours, minutes, and seconds read from the watch?SecondsMinutesHours1st2nd3rd
56Quiz3. Before taking sights on the Sun, you sight the horizon and align the direct and reflected images of the horizon. Your Sextant reading is 1.8' on the arc.What is the IE?b. What is the IC?+1.8'-1.8'
57Quiz4. Before taking sights on the Sun, you sight the horizon and align the direct and reflected images of the horizon. Your Sextant reading is 58.2' off the arc.What is the IE?b. What is the IC?-1.8'+1.8'
58Quiz5. You need to use the shade glasses on the sextant when taking sights on the sun.a. Trueb. False
59Quiz6. You take a run of sights on the Sun with the following times of sights and sextant altitudes. Which of the sights are probably erroneous?WT hs° 01.4'° 57.8'° 58.7'° 50.1'° 50.0'° 45.8'Bad SightBad Sight
61Quiz7. What is the purpose of "swinging the arc" when taking a sight with a sextant?a. To help obtain a clear view of the horizon.b. To be sure that the sextant is horizontal at the time of the sight.c. To help focus the body in the sextant telescope.d. To be sure that the sextant is vertical at the time of the sight.
62End of Junior Navigation Chapter 2 The SextantEnd ofJunior NavigationChapter 26262