6 NOON Latitude

7/31/2019 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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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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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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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

Documents

6 NOON Latitude