Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 Lighthouses in the Sky Junior Navigation Chapter 1 N E 5 Hostile Vessel Operating in this area.

Similar presentations


Presentation on theme: "1 Lighthouses in the Sky Junior Navigation Chapter 1 N E 5 Hostile Vessel Operating in this area."— Presentation transcript:

1 1 Lighthouses in the Sky Junior Navigation Chapter 1 N E 5 Hostile Vessel Operating in this area

2 2 Learning Objectives Define terms: altitude, circle of position, geographical position, intercept, and celestial line of position. Define 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. Given altitude, determine the radius of a circle of position and vice versa. State why accurate time is important in celestial navigation. State why accurate time is important in celestial navigation. Describe the altitude-intercept method of plotting a celestial line of position. Describe the altitude-intercept method of plotting a celestial line of position.

3 N S hs 3 Terms Terrestrial Refraction Apparent Body Ho (Altitude) ha dip Geometrical Horizon Visible Horizon Apparent Line of Sight index correction (IC) Zenith Celestial Equator Celestial Sphere Dec Equator Latitude Nadir Celestial Horizon GP Geoidal Horizon Sensible Horizon Observer’s Eye he DR Astronomical Refraction Parallax Body SD UL LL COP GHA & Dec Longitude When body is at your zenith: Latitude = Dec and Longitude = GHA

4 4 (cos LHA x cos Lat x cos Dec) + (sin Lat x sin Dec) = sin Hc convert sin Hc to Hc (calculated sextant height) Difference between Hc and Ho provides distance from your DR to COP. [sin Dec – (sin Lat x sin Hc)] / (cos Lat x cos Hc) = cos Z convert cos Z to Zn provides direction (azimuth) to GP. Law of Cosines

5 5 The Fundamental Idea In AP, a Radar Fix was determined by plotting two LOPs taken from radar. In AP, a Radar Fix was determined by plotting two LOPs taken from radar.

6 6 Plotting a Circle of Position You need to know: You need to know: Direction from observer to the GP of the body; and Direction from observer to the GP of the body; and Distance from observer to the GP of the body; but first – Distance from observer to the GP of the body; but first – You need to know how to convert altitude difference to nautical miles. You need to know how to convert altitude difference to nautical miles.

7 7 Angular Distance Radius of a circle of position is equal to 90° minus the altitude (1º latitude = 60nm). 90º – 90º = 0º 0º x 60nm = 0nm 90º – 0º = 90º 90º x 60nm = 5400nm 90º – 30º = 60º 60º x 60nm = 3600nm ?

8 8 COP and Altitude At 1034 an observer in Galveston measures the sun’s altitude to be 77°41.5´. What is the radius of the COP? At 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 = nm 18.5´ x 1 nm/minute = 18.5 nm Total = nm (radius of COP)

9 9 COP and Altitude At the same time observer in Los Angeles measures the sun’s altitude to be 57°34.1´. What is the radius of the COP? At 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 = nm 25.9´ x 1 nm/minute = 25.9 nm Total = nm (radius of COP)

10 10 Altitude-Intercept Method At a sight of the sun is taken. Recorded altitude = 57°34.1’ COP 1,945.9nm At a sight of the sun is taken. Recorded altitude = 57°34.1’ COP 1,945.9nm

11 11 Altitude-Intercept Method Calculate true bearing (azimuth) and altitude (Hc) from DR using Law of Cosines Calculate true bearing (azimuth) and altitude (Hc) from DR using Law of Cosines to GP Zn

12 12 Altitude-Intercept Method Difference between Ho (observed altitude) and Hc (calculated altitude) is the intercept Difference between Ho (observed altitude) and Hc (calculated altitude) is the intercept Ho 57º 34.1’ Hc 57º 24.1’ Diff 10.0’ towards Intercept 10.0nm 10nm COP drawn as a straight line perpendicular to the azimuth COP drawn as a straight line perpendicular to the azimuth When Hc is greater than Ho, your azimuth is the reciprocal of computed azimuth.

13 13 Altitude-Intercept Method Label with time of sight and name of body Label with time of sight and name of body Sun

14 14 Altitude-Intercept Method When you have only a single LOP, you obtain an estimated position (EP) When you have only a single LOP, you obtain an estimated position (EP) Sun

15 15 Quiz 1. 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.

16 16 Quiz 2. Polaris (the North Star) is located exactly over the earth's north geographic pole. a. True b. False

17 17 Quiz 3. The vertical angle measured with a sextant between a celestial body and the horizon is called: a. azimuth. b. intercept. c. altitude. d. zenith.

18 18 Quiz 4. 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 ' x 1nm/' = +33.9nm 3,153.9nm

19 19 Quiz 5. The difference between the calculated altitude (Hc) and the observed altitude (Ho) is called: a. azimuth. b. co-altitude. c. altitude. d. intercept.

20 20 Quiz 6. The method used in plotting a celestial LOP is called “the altitude-intercept method”. a. True b. False

21 21 Quiz 7. 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. True b. False

22 22 Lighthouses in the Sky End of The Sextant Junior Navigation Chapter 2

23 23 Learning Objectives Identify the parts of a sextant and understand how a sextant works Determine index error & index correction Describe how to handle, maintain & stow a sextant Describe techniques for taking Sun sights Describe safety procedures for taking sights on a boat Record the time of a sight Identify the ideal & practical accuracy limits Identify erroneous sights in a run of sights Describe the sight requirements for JN

24 24 Parts of the Sextant Index Arm Lanyard Handle Frame Limb Arc (degrees) Micrometer (min) Vernier (tenths) Horizon Glass Index Mirror Horizon Shades Index Shades Telescope Release Clamp WholeSplit Horizon Sight Tube 2X or 4X Telescope

25 25 How a Sextant Works The sextant set to 0°00.0´ The horizon will appear as an unbroken line when the sextant is correctly adjusted Split Field Full Field

26 26 How a Sextant Works Telescope aimed at the horizon Index arm adjusted to the appropriate angle Split Field Full Field

27 27 Reading a Sextant Accurate reading is necessary Accurate reading is necessary 0.1’ of arc equals 0.1 nm 0.1’ of arc equals 0.1 nm Full turn of micro drum Full turn of micro drum moves index arm one degree moves index arm one degree Vernier - auxiliary scale to interpolate the minute scale of micrometer drum Vernier - auxiliary scale to interpolate the minute scale of micrometer drum

28 28 Reading the Measured Angle 1. 1.First read degrees from the arc 2. 2.Then read minutes from micrometer drum 3. 3.Finally read tenths of minutes from vernier

29 29 Reading a Measurement Index Mark 40 ° 40 ° 02’ Read the Drum Read the Vernier 40 ° 02.6’ Read the Arc

30 30 Reading a Measurement 32.6’ 51.3’23.0’

31 ASTRA IIIB THIS INSTRUMENT IS FREE OF ERRORS FOR PRACTICAL USE Sextant Error Non-adjustable error Non-adjustable error Adjustable error Adjustable error Telescope axis - not parallel to frame Telescope axis - not parallel to frame Index mirror - not perpendicular to frame Index mirror - not perpendicular to frame Horizon glass - not perpendicular to frame Horizon glass - not perpendicular to frame Index mirror and horizon glass are not parallel when sextant set to 0°00.0´ Index mirror and horizon glass are not parallel when sextant set to 0°00.0´ Checking & adjustment procedures in Bowditch Checking & adjustment procedures in Bowditch Should only be made by experienced persons Should only be made by experienced persons Frequent adjustment might loosen screws Frequent adjustment might loosen screws

32 32 Index Error (IE) IE is common IE is common In good quality metal sextants In good quality metal sextants IE tends to remain fairly constant IE tends to remain fairly constant In plastic sextants In plastic sextants Checking IE critical Checking IE critical

33 33 Determining Index Error (IE) Set sextant to 0°00.0´ and sight on horizon Set sextant to 0°00.0´ and sight on horizon If 2 images of horizon not superimposed OR If 2 images of horizon not superimposed OR If horizon shows as broken line If horizon shows as broken line IE present IE present

34 34 Determining Index Error (IE) To determine value of IE. Adjust micro until horizon appears as straight line. Adjust micro until horizon appears as straight line. IE is the sextant reading: IE is the sextant reading: If index mark is below 0°00.0´ is off the arc If index mark is below 0°00.0´ is off the arc If index mark is above 0°00.0´ is on the arc If index mark is above 0°00.0´ is on the arc Full Field Split Field 0 ON THE ARC 0 OFF THE ARC

35 35 Index Correction (IC) IC - value applied to the altitude measured to correct for IE IC - always opposite to the sign of IE IE ‘on the arc’ requires negative IC When it’s on, take it off IE ‘off the arc’ requires positive IC When it’s off, put it on When it’s off, put it on 0 ON THE ARC 0 OFF THE ARC

36 36 Index Error When 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´ On 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 off 0

37 37 When 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´ On 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 on 0 Index Error

38 38 Caring/Cleaning for a Sextant Delicate precision instruments Delicate precision instruments Handle sextant by grasping its frame or handle - never by its limb, index arm, or telescope Handle sextant by grasping its frame or handle - never by its limb, index arm, or telescope Avoid touching mirrors except to clean them Avoid touching mirrors except to clean them Set sextant down on its legs - never mirror side Set sextant down on its legs - never mirror side Never put sextant where it can fall Never put sextant where it can fall Stow sextant in its case in a secure spot Stow sextant in its case in a secure spot Clean mirrors with lens paper or soft lint-free cloth Remove salt spray with fresh water Lubricate with light coat of fine instrument oil

39 39 Sight-taking Supplies Familiarize yourself with your sextant Practice taking sights at a beach or pier Natural horizon vs. dip short of the horizon Natural horizon vs. dip short of the horizon When comfortable, take sights from a boat When comfortable, take sights from a boat Sextant (obviously) Sextant (obviously) Watch with second hand Watch with second hand Notebook/pencil – record sight data Notebook/pencil – record sight data Chart of the area Chart of the area Tape measure Tape measureTHEN

40 40 Bring Down the Sun Set sextant to 00°00.0´ Move all horizon shades into position Aim it up at the sun Sweep sky to find sun If sun not visible, remove shades, one at a time When visible, select index shades of same density

41 41 When the Sun is caught Release and slowly move index arm forward while rotating sextant downward Keep sun in view in telescope constantly Continue until you are near the horizon Adjust horizon shades, if needed Sun also seen near horizon Bring Down the Sun

42 42 When sun’s image near horizon Release clamp to reengage tangent screw Bring sun to appear on the horizon, then Bring Down the Sun

43 43 Swinging the Arc

44 44 Recording Sextant Altitude  Call out “Stand by” to Recorder  Recorder responds “Ready”  Adjust micrometer drum to place sun on horizon  When sun on horizon, call “Mark”  Recorder notes time:  Seconds, minutes, hour – in that order  Read angle from sextant for Recorder  Repeat steps for a run of sights

45 45 Alternate Method  To take sights at predetermined intervals  Call out “Stand by” to Recorder  Recorder responds “Ready in xx seconds” and begins countdown  During countdown, adjust micrometer drum to keep sun on horizon  Recorder calls “Mark” when countdown complete  Recorder notes time:  Seconds, minutes, hour – in that order  Read angle from sextant for Recorder

46 46 Taking Sights at Sea Taking sights at sea can be difficult, sometimes dangerous Taking sights at sea can be difficult, sometimes dangerous Use a safety harness Use a safety harness Techniques: Hit and Run; Wait and See Techniques: Hit and Run; Wait and See

47 47 Special Techniques Dip short of the horizon Dip short of the horizon Acceptable for JN sights Acceptable for JN sights Back sight Back sight Acceptable for JN sights Acceptable for JN sights Artificial horizon Artificial horizon Not acceptable for JN sights Not acceptable for JN sights OK for practice sights OK for practice sights See Appendix A for details See Appendix A for details

48 48 Accuracy of Sights Modern marine sextant - readable to 0.1 ´ Modern marine sextant - readable to 0.1 ´ Nautical Almanac data are given to 0.1´ Nautical Almanac data are given to 0.1´ Sights timed to nearest second Sights timed to nearest second Error of 1 second in time lead to error of 0.25´ of arc Error of 1 second in time lead to error of 0.25´ of arc Practical Accuracy limited by: Skill of Observer Skill of Observer Quality of Sextant Quality of Sextant Stability of observing platform Stability of observing platform Visibility & Atmospheric Conditions Visibility & Atmospheric Conditions Practice – Practice – Practice

49 49 Runs of Sights Taking several sights on a body improves accuracy Taking several sights on a body improves accuracy Corresponding altitude changes should be proportionately constant Corresponding altitude changes should be proportionately constant Positive direction for rising bodies Negative direction for setting bodies

50 50 TimeDifferenceDifferenceAltitude °06.2’ °55.8’ –10.4´ °45.7’ °50.8’ °25.6’ –10.1´ +5.1´ –25.2´ 58s 56s 55s 58s Run of Sights

51 51 Graphing a Run of Sights

52 52 JN Sight Requirements Two Sun sights simulating RFix Two Sun sights simulating RFix One upper and one lower limb sight One upper and one lower limb sight Acceptable accuracy of all sights is 5nm Acceptable accuracy of all sights is 5nm Qualified ‘run’ of sights Qualified ‘run’ of sights Sights with altitude greater than 75 ° are discouraged Sights with altitude greater than 75 ° are discouraged Recording your sights Recording your sights USPS Sight Log Form USPS Sight Log Form Sight Folder must be completed before you can take exam Sight Folder must be completed before you can take exam Details in Appendix D Details in Appendix D

53 53 JN Sight Requirements Jun Sun LL Sun UL º 45.4’ 35º 51.4’ 36º 02.8’ 36º 14.2’ 36º 24.8’ 47º 00.8’ 46º 55.8’ 46º 49.4’ E W Ds º 29.9’N 92º 18.7’W Sun LOP, KP by GPS, DST, D1.3m fm chart Sun LOP, KP by GPS, DST, D180yd fm chart Art Mollica (E066699)St Paul1 of 1 “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ Arthur Mollica Sight 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 º 42.6’ º 38.4’ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “

54 1. When reading sextant altitude, in what order are degrees, minutes, and tenths of minutes read? Degrees Minutes Tenth of Minutes 1 st 2 nd 3 rd Quiz

55 2. When timing sights, in what order are hours, minutes, and seconds read from the watch? Seconds Minutes Hours 1 st 2 nd 3 rd Quiz

56 3. 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. a. What is the IE? b. What is the IC? +1.8' -1.8' Quiz

57 4. 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. a. What is the IE? b. What is the IC? -1.8' +1.8' Quiz

58 5. You need to use the shade glasses on the sextant when taking sights on the sun. a. True b. False Quiz

59 6. 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 Sight Quiz

60 hs WT Quiz

61 7. 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. Quiz

62 62 The Sextant End of Junior Navigation Chapter 2


Download ppt "1 Lighthouses in the Sky Junior Navigation Chapter 1 N E 5 Hostile Vessel Operating in this area."

Similar presentations


Ads by Google