6 NOON Latitude
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Transcript of 6 NOON Latitude
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WHY
lTraditionally the NOON Sight is VeryImportant to Navigators as his Day Starts
at NOONlThe NOON Sight gave the Navigator the
Distance Run in the Past 24 Hours
lYou will be learning how to obtain yourLatitude from a NOON Sight Observation
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WHAT
lHow to determine when it is Noon?lHow to Find Latitude by Observing the
SUN at Noon
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HOW
lYou FIRST determine WHEN NOONoccurs for You
lDo a series of Sights at Your NOONlReduce your Sight to your HolFind the SUNs Declination at the Time
of NOON Sight
lCalculate the ZENITH DISTANCElCombine Declination and Zenith
Distance to obtain Your Latitude
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New Terms
lMeridian Passagel
ZenithlZenith Distance
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Meridian PassagelThe moment in Time that the Subject Body
is located on a Specific Meridian (Yours)
lAll bodies have a Time of being on a givenMeridian
lCelestially known as Noon with the SunlUsually referenced to the Sun being on the
Observers Meridian
lThis is known as Local Apparent Noon
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Zenith
lIndicates a Point Directly OverheadlIf an Observer is at a Bodys GP, the
Body is in the Observers Zenith(directly overhead)
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Zenith Distance
lMathematically, the complement of theObserved Altitude
lZenith Distance = 90 HolZenith Distance is the side of the
Navigation Triangle that is between theObserver and the GP of the Body
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When is it NOON?
NOON is the Time that the SUN crossesyour Meridian Your Longitude and the GHA of the SUN are
the same value
it is NOT when you get hungry
it is NOT 12:00:00 though it couldbeNO
NO
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The Noon Diagram
Meridian
Equator
Zenith Distance
Declination
Latitude
DR
SUN
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How is the Time of Noon Determined?
lThe Time of Meridian Passage is noted inthe Nautical Almanac for each day.lThis Time is the Local Time at the CENTER
of each Time Zone
lThe Navigator MUST determine how farfrom the Center of his Time Zone he islocated
lThis angular difference is converted (Tablein Almanac) to Time, which is then Added (ifWest of the Center) or Subtracted (if East ofthe Center) from/to the Meridian PassageTime as found in the Almanac
lThe Time thus found is the Local Time ofNOON
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Example
l11 March 2011 You are located at aDR position of 21 - 25 N 068 50 W
lWhat Time is LAN?lGo To the Bottom of the Right Daily
Page of Nautical Almanac for 11 March2011 (in handouts)
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Page NA 11 in the Excerpts Book
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LAN Calculation
lMeridian Passage from the nauticalAlmanac is 12:10 on 11 March 2011
lYour DR Longitude is 68 deg - 50 minWest of Greenwich
lNow go to the Conversion of Arc toTime table in the Nautical Almanac
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Page NA-17 in the Excerpts Book
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LAN Calculation
12:10:00 Meridian Passage
+ 4:32:00 68 Longitude (West)
+ 03:20 50 Longitude (West)
16:45:20 GMT of LAN at your location- 5:00:00 Zone Description
11:45:20 LMT of LAN at your location
(we should be shooting the Sunat least 15-20 minutes earlier)
Note: that our Longitude estimate is very critical fordetermining the time of LAN & when we start
shooting
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The NOON Sight 1 Before and During
lThe Navigator prepares to startshooting the SUN approximately 15 -
20 minutes before LAN (approx.1125-1130 in our Example)
lSights are taken as every minute until3 minutes before LAN (1142), thentaken at as quickly as possible until 2minutes before LAN
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The NOON Sight 2 During and After
lDuring that 4 minutes when theNavigator is shooting the SUN the
Navigator should notice that the SUNhas stopped rising, then hangs inplace, then starts to fall.
lSights are then taken for about 5minutes or more after LAN to ensurethat the Sun is indeed falling
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Graphing Multiple Sights
Before and After Noon
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Determination of Latitude
l Correct the Sextant Altitude (Hs) toyour Observed Altitude (Ho) in the
usual mannerlSubtract the Ho from 90 this is your
Zenith Distance
lFind the Declination of the SUN for theTime of your Sight (in GMT) in theNautical Almanac
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CHAPMAN SCHOOL OF SEAMANSHIP
l11 March 2011 You are located at21 25 N 068 50 W
lWe obtained an altitude of 64 55.4 forthe Suns Lower Limb at 11:45:20 LMT.Our height of eye is 115 above sealevel. Our Sextant IC is 0.
lGo To Table A2 of the Nautical Almanacfor the necessary Correction values (inhandouts)
EXAMPLE DATA
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CHAPMAN SCHOOL OF SEAMANSHIP
Table A2 Information Page
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Subtract
Insert the Height of Eye correction and Compute HaThen go back to Table A2 with the Ha to get the Alt Corr.
Now go back to Table A2 with the Ha to get the Alt Corr.
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CHAPMAN SCHOOL OF SEAMANSHIP
For the SUNs Lower Limb inMarch with an Ha of64 45,
we find thatthe Alt Corr. is +15.8
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Subtract
RESULT
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Find Declination for your Sight Time
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Find d factor
The d Factor is the amount of change in Declination in anhour in our example it is 1.0 per hour
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Find the d
Correctionin the
Increments
and
Corrections
pages forthe
minutes of
GMT for
your sight
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CHAPMAN SCHOOL OF SEAMANSHIP
Find the d Correction in the Increments and Correctionspages for the minutes of GMT for your sight in this case for
a d of 1.0 the Correction is 0.8 for 45 minutes of GMT
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Place the values of the Zenith Distance and Declination inthe appropriate boxes at the bottom of the Form to
Calculate your Latitude at the time of the Sight.
SUBTRACT
RESULT
We are 5.4 nm South
of our DR
We were looking
South at the SUN So we
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COMPLETEDNoon Sight
Form
for
this example
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Summary
lYou have Learned How to Determinethe time of LAN
lYou have Seen How to Determine yourLatitude from your NOON Sight