Meridian passage and calculation of latitude

Meridian Passage AND Calculation of Latitude Today’s lesson Aim is:To introduce you to the theory of Meridian Passage, why we obtain it and how we calculate the observer’s latitude The Objective being:That by the end of this two hour lesson YOU will be able to:Explain the theory of Meridian Passage and position lines Explain why navigators use this theory to obtain position lines and latitude Demonstrate how to extract the LMT of Meridian Passage from the Nautical Almanac Calculate the GMT of Meridian Passage by applying longitude Demonstrate how to obtain Declination and necessary corrections from the Nautical Almanac Calculate a meridian passage latitude using the supplied pro-forma layout Meridian Passage When we talk about Meridian Passage, the Meridian we are referring to is the Observer’s Celestial Meridian Please remember that Meridian Passage Meridian Passage occurs when the celestial body, in it’s movement across the heavens crosses the observers celestial meridian At this point the bearing of the body is either due north or due south of the observer and the altitude of the body is at it’s maximum Body bearing North or South Here we have the OOW at 100 North Latitude observing a body on his/her meridian which has a Declination of 100 S Pn Observers Meridian Equinoctial W Z E Q X Ps OBSERVERS MERIDIAN Meridian Passage As we already know, taking an altitude of a celestial body allows us to calculate it’s bearing and as a result, a position line Observing the Altitude at Meridian Passage provides a quick and easy method of obtaining a position line which, as the bearing of the body is either due north or south then the position line will run in an east/west direction This same position line in effect will then become the observer’s latitude Here we have a 2/O at 100 North Latitude observing a body with a Declination of 100 S Pn Pn P Observers Meridian Equinoctial Z Z Z W E Lat Q Q Dec Dec X TA Ps PsX ZX Meridian Passage In order to make the observation at the correct time we need to know the time of meridian passage We also need to know the GMT of meridian passage in order to extract the declination of the body from the Nautical Almanac In order to find the time of meridian passage for the sun & planets we enter the Nautical Almanac daily pages and extract the time of Mer Pass as follows:- Meridian Passage These times are the LMT of the local Meridian Passage of the body We must apply longitude (in time) to this time in order to obtain the GMT of Meridian Passage at the local meridian before we can extract Declination from the Nautical Almanac A little problem for you! • On September 23rd The Sun is observed on the meridian in DR position Lat 120 15’ N, 0920 45’ W Find the time of meridian passage and the declination • LMT Mer Pass: • Long (W) • GMT Mer Pass 23d 11h 52m 06h 11m 23d 18h 03m • Dec’l • “d” (1.0) • Dec 000 23.9’S 0.1 + 000 24.0’S Procedure for Altitude correction to derive Latitude by Meridian Altitude • • • • • • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction True Altitude ~900 00.0’ ZX + or – Dec Latitude 450 25.5’ 00.2’ 450 25.7’ So tell me, was the IE on or off the arc? 8.7’ + or - ?? 450 17.0’ 000 15.3’ Lower limb + or - ?? 450 32.3’ : 900 00.0’ : 440 27.7’ : ??0 ??.?’ : ??0 ??.?’ N/S Position Line runs 0900 / 2700 : : : : : : : Applying Declination to ZX Let us imagine we are on the Celestial Sphere, looking down on a 2/O on the Equator Pn with Sextant in hand Pn Z W What does this line also represent? Z N E S What does this line also represent? Ps Ps Applying Declination to ZX Let us now imagine the 2/O moves to 100 North and observes a body with Declination of 100 S Pn ZX Observers Meridian Equinoctial W Z Z Q Dec E Pn X Lat Q TA X TA Ps S N Applying Declination to ZX Let us now imagine the 2/O moves to 100 North and observes a body with Declination of 100 S Pn P Observers Meridian Z Equinoctial W Z E Lat Q Q Dec X TA Ps X ZX Applying Declination to ZX Let us now imagine the 2/O moves to 200 North and observes a body with Declination of 100 N P Pn Observers Meridian Z Equinoctial W ZZ E ZX X Dec X Q Q TA Lat Going back to our original example • • • • • • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction True Altitude ZX + or – Dec Latitude 450 25.5’ 00.2’ 450 25.7’ 8.7’ 450 17.0’ 000 15.3’ 450 32.3’ ~900 00.0’ : 440 27.7’ :: ?? 240 ??.?’ 27.7’S : 200 00.0’N : : : : : : : P Z Lat Q Dec X ZX [...]... Meridian Passage These times are the LMT of the local Meridian Passage of the body We must apply longitude (in time) to this time in order to obtain the GMT of Meridian Passage at the local meridian before we can extract Declination from the Nautical Almanac A little problem for you! • On September 23rd The Sun is observed on the meridian in DR position Lat 120 15’ N, 0920 45’ W Find the time of meridian. .. 100 North and observes a body with Declination of 100 S Pn ZX Observers Meridian Equinoctial W Z Z Q Dec E Pn X Lat Q TA X TA Ps S N Applying Declination to ZX Let us now imagine the 2/O moves to 100 North and observes a body with Declination of 100 S Pn P Observers Meridian Z Equinoctial W Z E Lat Q Q Dec X TA Ps X ZX Applying Declination to ZX Let us now imagine the 2/O moves to 200 North and observes... meridian passage and the declination • LMT Mer Pass: • Long (W) • GMT Mer Pass 23d 11h 52m 06h 11m 23d 18h 03m • Dec’l • “d” (1.0) • Dec 000 23.9’S 0.1 + 000 24.0’S Procedure for Altitude correction to derive Latitude by Meridian Altitude • • • • • • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction True Altitude ~900 00.0’ ZX + or – Dec Latitude. .. now imagine the 2/O moves to 200 North and observes a body with Declination of 100 N P Pn Observers Meridian Z Equinoctial W ZZ E ZX X Dec X Q Q TA Lat Going back to our original example • • • • • • • • • • • Sextant Altitude Index Error (I.E.) Observed Altitude Dip Apparent Altitude Total Correction True Altitude ZX + or – Dec Latitude 450 25.5’ 00.2’ 450 25.7’ 8.7’ 450 17.0’ 000 15.3’ 450 32.3’ ~900... 25.5’ 00.2’ 450 25.7’ So tell me, was the IE on or off the arc? 8.7’ + or - ?? 450 17.0’ 000 15.3’ Lower limb + or - ?? 450 32.3’ : 900 00.0’ : 440 27.7’ : ??0 ??.?’ : ??0 ??.?’ N/S Position Line runs 0900 / 2700 : : : : : : : Applying Declination to ZX Let us imagine we are on the Celestial Sphere, looking down on a 2/O on the Equator Pn with Sextant in hand Pn Z W What does this line also represent?