LIBRARY
General Note
How would I subtract Degrees and minutes: 47 degrees 07.2 minutes (that’s my position ..I want to subtract - 22 degrees 28.7 minutes ANS: Take the 47 degrees make it 46 degrees since there are 60 mts. to a degree.. the (07.2) becomes 46 degrees (67.2) mts. Now just subtract as usual.
Conversely add 47 degrees 48.2 mts
+ 22 degrees 28.9
ANS: add your minutes 77.1 mts
degrees of course add up 69 degrees
70 degrees 17.1 mts.. convert the minutes to degrees 77.1 mts
equals 1 degree 17.1 minute. (convert and add)
Notes On Doing a Starline
The information you want from a Starline is exactly the same as in a Sunline. The procedure is exactly the same. Obviously when you access the worksheet, it’s stands to reason the format would be the same; except, for one additional step. The reason for the additional step is because there are 57 available stars in the Nautical Almanac only one Sun. This affects ONLY your GHA calculation… as it relates to the Almanac layout. The rest is exactly the same.
Before I get to this, I want to say that the hardest part of a Starline, unlike the Sunline is obviously identifying the star or stars in the heavens. Fortunately this is a relatively simple procedure. You do not need to understand any astronomy or spend time studying celestial formations. You will need a template device called a Star-finder (this is covered below and is quite simple). The second hardest part, after identifying the star or stars you intend to shoot are conditions…You will need to have enough light for a visible horizon; twilight is generally the most ideal time, providing the sky renders suitable candidates for your sextant.
After you get a star’s HS the corrections off the Almanac cover to HO are the same… Just make sure that the information you are accessing is under the heading "Stars & Planets" and NOT under the Sun’s headings. Go into the Library and access the Starline daily almanac sheet so you can get an idea of what information you are dealing with.
You’ve learned that once you have your GMT of the Celestial body’s sextant angle HS, you have the required information to enter into the Nautical Almanac to obtain GHA & Declination of the celestial candidate. Armed with the correct day and time, you found the heading for the Sun in the first column on the second page. You then copied the GHA for the whole hour…to the immediate right you copied the declination. The appropriate heading for a star is to be found in the very first column on the first page for the appropriate day and whole hour... "just like the Sun"…The heading is called Aries Copy down the GHA and put it on your worksheet…What no declination?…Since there are 57 stars….the book has been condensed. Now exactly as you did in a Sunline correct the GHA for minutes & seconds…found of course in the Increments & Corrections pages.. located near the back of the Almanac. After you have the complete GHA of Aries…look over on the right hand column on the same page. There listed you will find "all 57 stars". Simply copy down the value of SHA to be added to the GHA of Aries…"It’s on the worksheet…Before you do that though; to the right of the SHA you will find Declination copy it down ..no correction necessary and your on your way. Look at Aries as kind of a generic star, employed to keep the Almanac to manageable size…The SHA…customizes Aries… sought of a "Signature" of the star…in addition to rendering its Declination. Again access the Starline Almanac sheet in the library to see what I'm talking about
How to find Stars:
The Starline worksheet indicates only one additional step in the arithmetical process of attaining our desired (Z and HC) from our original Sunline solution. That's the good news, the bad news is this. We all can readily identify the sun in the sky, but as we look into the night sky, for most of us, the only apparent celestial body that is readily recognizable is the moon.
On each almanac page there is a listing of 57 stars. They are grouped in five's, the last grouping two.. Each star entry renders the information required for the aforementioned additional step i.e. its (SHA & DEC). Obviously if you knew what star or stars you are dealing with you could complete your worksheet in obtaining the three arguments necessary to enter into (Old Maroon- Ho229 tables) and solve for Z and HC. Easy enough, if only we knew which stars are which. After all there are thousands of stars in the heavens, much less finding and identifying three of 57.
You have learned enough at this point to make this process quite simple. You will need to go to your local marine supply store, or order over the net. You don't have to put down several hundred dollars for a celestial computer. Because of your hard work to this point, only a thirty-dollar outlay is necessary for a Weems & Plath Star-finder also known as 2102-D.
For 30 dollars you have a nice U shaped black case with a round shaped white plastic disk. One side is for the Northern Hemisphere, the other for the Southern. All the 57 stars that aids us in determining an LOP are engraved on this disc…North and South. You also get 10 transparent templates. We will concern ourselves with nine of them. The first template is marked 5 degrees latitude, the second one 15 degrees latitude and so forth…the ninth 85 degrees. Now you take the template nearest to your DR latitude. Place the appropriate template over the white disc. You will notice the 360 hash marks on the outer perimeter of the white disc similar to a compass. If it is centered properly as any five-year-old can do, you will notice an arrow on the template, which can align with the compass hash marks. This is where your knowledge comes into play. You need only to calculate the LHA of Aries, then align the template arrow to the LHA as indicated by the appropriate compass hash mark on the white wheel, and the names of candidate stars become identifiable.
Let's say my LHA Aries is 182 degrees. Using my starfinder it's my intention of picking out three stars in order to take a fix. My starfinder graphically tells me that Antares is a bright star located HO- 21 degrees, Z- 121 degrees. This is easily confirmed by aligning it up with your compass. Antares will indicate its presence at 121 degrees give or take 5 degrees. Now get your sextant out to confirm its HS…If it approximates 20 degrees or so you have confirmation that you have indeed identified Antares. If there is any doubt your Star -finder indicated a star of first magnitude. The Star-finder indicates the 57 stars as first, second or third magnitude. First being the brightest category.
Let's pick out two more candidates Sirius another first magnitude star is located at HO- 10 degrees off the horizon at approximately Z- 255 degrees off the compass, Acrux HO- 22 degrees Z -177 degrees Azimuth. Now that we have identified three likely candidates for LOPS that will render a celestial star fix, it's time to get to work and do it.
Let's back up a second and review what we have and review the process that is ultimately going to render us a star fix. First we need to review how to get our LHA Aries which will allow us to use our Star-finder. Follow your worksheet and get your GHA Aries, which you will find by utilizing the Nautical Alaminac. Now add or subtract your Longitude, depending on whether your are East or West Longitude, same as you did in a Sunline this will allow you to use your Star-finder because now you have the LHA of Aries.
Now you are in a position for serious sight reduction solutions for three stars. Get your sextant and shoot HS's of Antares, Serius and Acrux… just as you learned in sight reduction for the sun.. Your one additional step is adding on your worksheet the SHA's of the three respective stars for each star solution. You are obviously using three worksheets to keep thing simple and organized. You should be quite aware that to enter into HO 229 you need three arguments Assumed Lat., Declination and LHA…The star's LHA is found of course by taking the corrected SHA and either adding or subtracting your longitude position. You will of course have noticed that next to the star's SHA in the almanac is its declination which needs no correction. So now you have your three arguments to complete your calculated HC and Z for each star to be compared to your observed solution found on your sextant thanks to your star-finder. The application of HOMOTO will render your LOP. The intersection of your LOP's will give you a Celestial Star Fix.
Now taking a look at the Three Star Worksheet should present little problem in understanding if you have some experience and familiarity with the Starline Worksheet. Basically it's just a condensed version in an attempt to accommodate the calculations for three stars. A worksheet such as this is of primary importance. Why? Application is not the problem, accuracy is when you consider one minute off represents one nautical mile. If you are really serious about this application, the only thing I can say is, that it's all there for you…," practice, practice, practice.
To my mind a three star fix is the Soul of Celestial Navigation. To practice you don't even need a sextant. What you need is your aforementioned Star Finder, a Nautical Almanac, An HO-229, any volume will do and a Universal Plotting Sheet. I would highly recommend printing out the Three Star Fix Worksheet from the links Library. The Starfinder provides you with an observed Altitude, even an azimuth. Use these in lieu of an observed altitude from a sextant. Compare them with the computed altitudes, then plot them for your fix. How accurate are they? "They will put you in the ballpark, even take you to the correct section...row and seat number you will need a sextant. Remember that a Starfinder identifies and points you in the right direction, the sextant gives you the refinement, this is as far as science takes you, using the sextant is the art. Nevertheless making up your own problems and plotting them is essential if you aspire to be a practitioner of the dicipline. Eg: It's December 1st, local time is 19:27, your DR position is Lat 26-21 N, Lon 74-14W. From your DR position sight three stars from your Star-Finder and plot a fix. I gave you all the knowledge you need to do this application. The rest is up to you. There are hundreds of examples that you can make up. When this routine becomes second nature, you are well on your way to becoming a practical celestial navigator.
Perhaps at this point a question that might be raised is this, could I navigate around the world with just a compass, a current nautical almanac, HO 229, a Universal Plotting Sheet plus a sextant and starfinder? If you consider and appreciate possibly in theory, you are beginning to have a pretty good understanding of celestial navigation. Remember it is very much an art as a science. On a practical note the last time I crossed the Pacific, from the Coast of Japan to the mouth of the Columbia River off the Coast of Oregon, you could hardly see a hand in front of your face for nine days rendering a sextant quite useless; nevertheless, you are beginning to master a form of obtaining a fix utilizing the celestial bodies. How you utilize this knowledge is part of your creativity as a navigator
Notes On Meridian Passage
We discussed at length how Longitude relates to the passage of the Sun each day; along, with the overhead noon aspect of the sun’s daily passage over the Prime Meridian and 23 other Standard Meridians.
Now access the sheet Meridian Passage LAN (Local Apparent Noon). First, thumb through the daily pages of the Nautical Almanac. Toward the bottom of page 2., you will see two small boxes, Sun & Moon. We are concerned only with the Sun box. Note where it says Mer Pass. Copy down the time…of Mer Pass for the day you are interested in on the worksheet. You will note that the Daily Pages are broken down into three day intervals on each page…make sure you get the proper time for proper day from the column on the immediate left… "When you see it however it will becomes immediately apparent."
If you thumb through "any" page, you will find that the time ranges from about 11:50 to 12:09…What that means is this. The indicated time is the "exact" time the Sun passes over each and every Standard Meridians THAT DAY….whether is be the 15 degree Meridian 30-45-60 etc….REMEMBER there are ONLY 23 Standard Meridian’s and one Prime. If you are on any one of those Meridians…you can throw the worksheet away because you would know when the daily event will take place. Chances are you are not…so we must adjust the time for our intended position since we will probably find ourselves somewhere East or West of a Standard Meridian.
Back to the Worksheet: For our desired day we found Meridian Passage will take place 11:50 (fill it in). From your present position calculate you DR position at 11:50 (If you don’t know how to plot a DR position review. A DR is a position based only upon speed distance and time) Now you would fill in your intended 11:50 Lat. & Long. On the next line, you would copy your intended DR Long…Now you would fill in your closest Standard Meridian.. In our case it reads like this [Fill in these values] Dr. LAT. 30 -45 N LONG. 47-17.3…fill in this DR long the next two lines down. The Nearest Standard Meridian to you DR position is the 45 degree Meridian…fill that in…… subtract the difference which is 2 degrees 17.3 minutes. Open up your Nautical Almanac… again toward the back you will find a table headed Conversion of Arc to Time the table tells you this… Find 2 degrees on the left hand column. It indicate "0 hrs. 08 minutes"…that’s how long it takes the sun to travel 2 degrees…. 8 minutes… Now look over onto the columns minutes and seconds. We see that the sun travels 1 minute and 9 second in 17.25 minutes of longitude arc.(close enough.) Therefore the adjustment we are required to make to know exactly when the sun will pass over our DR longitude of 47-17.3 is (fill it in on your sheet. Under the heading degrees fill in 0h 08m…under m & s fill in 1m 09s..add them fill in correction 09 m 09s…round off to 09 m. On the bottom fill in your first value 11:50…now fill in your correction 09 m.. Now read the instructions on the worksheet Since you are West of the event that occurred at 11:50 @ the 45 degree Meridian…It’s going to take the sun nine minutes longer to be overhead at your position at 47-17.3.. so "Add." The answer noon occurs at 11:59 over your intended DR position at close approximate time of event…
Whenever I referenced the noon event earlier in this link, i.e. understood to be 12:00 PM, I always qualified it with the words more or less (mol, perhaps now you might understand "Why". I also spent a lot of time explaining a relatively simple application, for two reasons. 1- To assure your understanding of how time relates to longitude…"We invested a lot of time on that concept in the main body". 2- When we calculate for Sunrise/Sunset, you will find the procedure is along the same lines so less explanation will be necessary.
Latitude By Meridian Altitude
In the preceeding solution ie Meridian Transit (LAN) The methodology of the solution was quite simple. You merely looked up in the Nautical Alamanac what time around noon the sun will pass the closest standard Meridian to your position. Actually the hardest part of this solution might have been finding where the Time/Arc conversion page was located in the Almanac and spending a few minutes in calculations. After a few times however, the realization will set in that you really don't need this table….Why? Well, if the Sun travels 15 degrees in one hour, it travels one degree every four minutes. Therefore if your DR longitude position is 77 degrees 37 minutes West, you are 2 degrees 37 minutes West of (Mer Pass) published that day for the Standard Meridian…. ie if Mer Pass in the Almanac is 11:51… and you know that the Sun travels one degree in four minutes it will take nine additional minutes to get to your position so at 11:59 the sun will be overhead ie on the same meridian as your vessel.
Now that I know this to be the case, stroll out on the bridge, take a sighting (HS) of the sun and make the appropriate corrections for (HO). Now subtract your (HO) from 90 degrees.This will give you the Zenith distance ie. the angle between you and the body. Since we know our zone time (ZT 1200 app.), calculate GMT from our 1200 PM ZT. This enables you to obtain from the Nautical Almanac the Declination of the Sun. Lastly either add or subtract (the result will be quite clear whether to add or subtract) the Declination from your Zenith distance calculation. The answer is your latitude. I'm not going into Celestial triganomic explainations. After doing it a few times, you may be able at this point to figure it out or simply look up the explaination in Bowditch yourself. This celestial procedure is obviously quick and easy. The benefits will soon become apparant, not only in verifying your latitude but keeping your sextant practice crisp and sharp. [ 90 degrees - (HO) = Z + or - Dec = Lat]
Azimuth
As mentioned in the main body, an Azimuth is a three dollar word for taking a bearing. The worksheet is designed to take an Azimuth off the Sun. Put the sextant away. Use whatever means available to find out the "exact" bearing of the sun…and the "exact" time you took the Azimuth. This is pretty much a standard required offshore procedure. The obvious question is just what is the purpose of taking an Azimuth. It’s purpose is to check the accuracy of your compass. Either on a Gyro compass where we are looking for mechanical error, or a magnetic compass where we are looking for magnetic deviation. Most of you who are "I guess at this point involved with this link" will realize the full measure, as your compass concerns are toward your magnetic compass. Gyro Compasses have nothing to do with magnetics. Magnetic compasses are subject to the influences of magnetic variation which is geographical, and deviation which are local generally on board influences.
You will first off note on the worksheet that it is somewhat similar to the Sunline and Starline sheets. As mentioned above a compass bearing is taken on the sun…"Put the sextant away no HS or HO is needed". Also as mentioned above, The time factor that the bearing or Azimuth was taken is equally as important as in a HS with a sextant…Put the Azimuth bearing value in on top line…also put it near the bottom next to the letter C….Where it says Position and Time…put in all your applicable information…Once you have your GMT.. Get your GHA and DEC information….same as in the Sunline procedure. Notice that the next line does not call for an assumed longitude… Just put in your regular DR longitude…no adjustment is necessary…You say that you will not have an even numbered LHA if you do that?…just put down what it comes out to be. Write in your arguments…At this point I’ll exemplify. The Azimuth or bearing on the sun was 294.5 degrees Fill it in on top and next to "C" toward the bottom.…I’m going to skip the routine stuff and give you your three arguments for 229 LHA 55-05.6…. DEC N 0-53.8 Lat. 18-23 S…Use 229 in the same fashion as you learned it. On Page 113… you will find the value of Z 102.2. The page is LHA 55 contrary ; DEC 0.; LAT 18….That’s your base Z…Fill in the BASE Z across the board i.e.. three times: under LHA…LAT…DEC. Where it says next.. what we are looking for is the next higher value Under LHA you will have to flip to the next page…The value will be found under LHA (56 contrary) Dec 0 Lat 18 Write in 101.8. Now flip back and do the next one Lat…The value of 55 LHA (19 Lat) Dec 0 is 102.8. "Now for the last one" LHA 55 contrary Lat 18 DEC (1) value is 103.3…Now you have all the information to do a classic 3 column Interpolation. "If you don’t remember how to do an Interpolation review your sunline sheet. You are just solving for Z… Notice there was no copying or reference to the value of HC…we don’t care about that… only Z…Z has to do with directions, bearings and Azimuths.. HC has to do with sextants HS and HO. When you solve your three interpolations the result is a total correction…use your sheet. The total correction comes out to +1.18. Now add that total correction to your base. Z= 103.4 degrees. Last step, check your 229 instructions. We are in South Latitude LHA is less than 180… so ZN =180+z =283.4. Fill that figure in under T. That’s the True bearing of the sun at the exact time you took it. Most of you probably have a magnetic compass. When you use your charts for navigation, you probably use the inner compass rose, the one referenced for a magnetic compass. The difference between the Inner rose, the magnetic bearings, and the outer rose the true bearings, is the "Magnetic Variation".. The chart will tell you what it is if you ever noticed it , inside the rose… like 11.2 W or 8.6 E. You can find it geographically from Pilot charts etc. In our example the variation is 8.3 W. Fill that in under "V". To solve the problem we only have to know one other thing…Do I add the variation or subtract? Like Admiral Homoto, there is another universal Navigator’s ditty. True Virgins Make Dull Companions At Weddings. T V M D C…at weddings T= 283.4… V= 8.3W (at weddings means Add West Subtract East) Therefore M=291.7…If your compass reading was 294.5 the compass deviation is 2.8…West or East ?…working down the TMVDC you know you must Add 2.8 to 291.7 to get 294.5…so apply [at weddings] the deviation must be 2.8W…’ Make up your own simple TMVDC examples using East and West variation and deviation until you have it down it must equal out….On a long offshore voyage get in the habit of checking your compass deviation each day…Once you get the hang of it, Taking an Azimuth on the Sun or a star becomes a 10 minute sailors routine.
Amplitude.
An Amplitude accomplishes the same result as an Azimuth. It can be particularly accurate for a smaller offshore vessel… who neither has a repeater on the wing with a fitted Azimuth circle or any other somewhat mundane device to assure accuracy of the bearing. Unlike an Azimuth which can be taken anytime between sunup and sundown. An Amplitude is taken only at sunup or sundown most accurate whenever the sun is centered on the horizon…It’s as easy as taking a bearing off a light house. One other advantage, 229 is not required. The tables come out of Bowditch, tables 27 & 28. So for the economical offshore navigator, besides his Nautical Almanac and Amplitude worksheet, 4 pages from Volume 2 of Bowditch Pgs. 169-172 are all that is necessary. Copies of the tables tucked between the covers of the Almanac.
Before we take a good look at the worksheet, it is worth noting that every Celestial problem encountered, which employs either a sextant angle or a compass bearing, has off the top, four sequences in common… 1-You obviously take your angle or bearing of the event. 2-You mark the exact time the event was taken. 3-You convert local time to GMT. 4-You open up your Nautical Almanac. These 4 sequences should become automatic, and taking an Amplitude is no exception.
Looking at the worksheet, the first thing that becomes apparent, is the small amount of information required from the Nautical Almanac . The GMT is used ONLY to get the Declination. No GHA, no m & s corrections , no longitude, no LHA… therefore no 229. Instead of the usual three argument of LHA, LAT and DEC….we only need two Lat and Dec. Substituting for "old maroon" are tables 27 & 28. In fact for practical purposes, the information derived from table 28 is hardly worth the effort…and after a few Amplitudes, I generally bypass it completely. For practice purposes…it’s a good drill to sharpen your Interpolation skills.
Back to the worksheet. After you get your Declination from the Almanac, you fill it in next to DEC under Table 27. Take your Lat position, and do the same. These are your two arguments to enter into table 27. The tables are arranged… Latitude in column form….Declination across the top. Take the base and a next the same as you did on the azimuth form. The most difficult thing about an Amplitude for someone learning, is really knowing how to properly do an Interpolation. What I mean is this. In 229 all your intervals were 1 degree.. you divided by 60. Here your intervals may be 2 degrees or 5 degrees meaning you would divide by 120 qnd 300 respectively. Likewise your increments may not be taken from the nearest whole degree but from the nearest half degree or 2 degrees. My advice is to review over the procedure that was learned in 229… then take a look at the application as it applies in 27 & 28. Remember in Interpolation the effort far exceeds the result. The result is only a correction to the BASE… but in most cases very important. After you interpolated for your corrections follow the worksheet add or subtract corrections to the base…Now you take your corrected base and if your Amplitude was made on the horizon at sunup add 90. If it was sundown on the horizon as the sun was setting add 270.. "Sun rises in the East, sets in the West." Your answer is your computed T… Fill it in next to T. The bearing (Amplitude) you took on the first line fill it in under C…Similar in form to your solution on the AZ worksheet.
Now with the same arguments used in table 27, Lat & DEC go into table 28…get your base…get your "next" and interpolate…Add or subtract the total correction to the base and ply it to C. You will probably find that all the work on table 28 doesn’t yield a result more than .1 to maybe .5 … particularly in the waters you will be sailing (take a look of the range of bases in 28 to get my point)..... except in our "unlikely" example,… where we are at Lat 62 S.. correction to the compass is 1.7 degrees "highly unlikely sailing in those waters" and although it’s good practice in the beginning, it allows me to avoid a lengthy explanation on the elevated pole. The only thing left is to apply your TVMDC procedure, in order to obtain your compass deviation. Although this may seem a bit dicey in the beginning.. after a week of doing an amplitude at sunset…you will find yourself practically doing it in your head within five minutes..so learn it and apply it….and develop your own shot cuts with application. Here are the numbers to plug into your worksheet to obtain a reasonably good answer. Remember this is not a test, if you are in the ball park you are doing fine.. accuracy comes only through practice. "If you are still with me and really want to know a final step that I left out of the solution E-mail me… it could be a bit confusing..and again the waters we all generally sail in offshore, do not warrant paying much attention to the correction on 28… I'll say it one more time...just take a look at the table bases and you’ll get the picture.." Be practical precision comes with having a good perspective in what you are doing..not a slave to the slightest bit of correction. This is more of an art than science.
Your bearing of the rising sun on the horizon 123.6 mag. Compass Declination S 19-23.4 DR Latitude 61-31.4 S Variation 7-20E
[ ANS True bearing 134.1] "Your base will be 43…total corrections +1.1 + 90 =134.1"
"Practice your Interpolation" "Practice TVMDC ..(at weddings) "
{Final ANS…Deviation 3.2 E}
Latitude & Azimuth By Polaris
This is a real Kool procedure. Not only will it keep you razor sharp in your application of Celestial… but it will again as in Lat. by Mer Alt. validate how accurate you are, and how accurate your sextant is. The big picture is this. We are taking a sextant altitude on Polaris to get an LOP and validate our Latitude, at the same time we take an Azimuth bearing of the star in order to find gyro or mag error. You will probably need to modify my worksheet for your purposes….You will notice my application is geared for a Gyro compass…You will probably need the full TVMDC (at weddings)
Polaris is called the "pole star" because it is about two degrees from the North Pole… You don’t need a star finder. If you look at the diagram on the worksheet, you can find it by observation of the " Big Dipper".
OK let’s tackle the worksheet: Do your standard 1-2-3-4 point procedure we discussed in the beginning of the Amplitude section. Get your GHA of Aries…. for the whole hour. After you correct for the mts and sec.. for the part hour…Use an assumed longitude as in a typical sun or Starline….then calculate your whole hour LHA… " Someone paying close attention might say…What no SHA? "It’s built into the Nautical Almanac tables.. We need go no further … leave 229 "old maroon" on the shelf. Thumb through the Almanac. Right before the Increments and Corrections table , you will locate "Polaris (pole star tables).. The first thing you should notice is the left hand column. Our three arguments are waiting for us… LHA of Aries…DR Lat… and "if you don’t know the month you are sailing in …what can I say". "Guess what +A0 +A1 +A2…are all about"?…They are your corrections added to HO…You then deduct 1 degree. What you will notice is that your corrected HO is close to your Latitude. Let me put it this way, if Polaris was "right on" the North Pole your latitude would equal your observed Sextant angle….I mean even at 2 degrees off the pole you’re pretty close. I’m going to give you the numbers to figure it out the solution….Remember ..just be in the ballpark don’t let the corrections stand in your way…If you are a purest you can go through an interpolation for A0… A1 & A2, or use a little logic and come close with a mental interpolation… "I mean it’s no harder than a train timetable" One last point.. The 4th column is the Azimuth correction. When you take your Azimuth and if it is not somewhere between 358 to 002… degrees… on a "gyro compass" You either have the wrong star or your compass needs serious adjustment… Think about what I said…and apply your TVMDC…Then think about this statement one more time. After you do it a couple of times with your magnetic compass you should get a pretty good read on Polaris through casual observation for quick compass check. Just plug in your latitude and LHA (314-XX.X) "you need to solve this arguement" and the tables will give you T….you know what C is and you "should" no at this point what variation you’re looking at. As a bonus if you don’t know what I am talking about.. there are instruction that come with this table.. and getting this far, in "what has turned out to be an epic…at least for me " should be easily understandable. Now for the numbers: Observation Polaris 359 per gyro compass, HO 35-43.0 (be careful use the worksheet…don’t overwork it) @5-30-21PM local time Nov 16. Position DR Lat 35-10N long 33-30W
Required Latitude and Gyro error.?
ANS: HO 35-43.0 +A0… 0-49.3 +A1… 0.4 mts + A2… 1.0 mts + 36-33.7 -1-00.0 = 35-33.7…That my calculated Latitude for want of a better word …compare that with my DR latitude..35-10 "pretty close"…You should start to understand that this is very much an art form.. practice leads to accuracy not a deeper understanding on Celestial events. By the way the gyro compass correction comes out to 1.1 degree.. Now if you had a magnetic compass to be corrected substitute 001.1 in the T…and apply VMDC…based upon what other information you have on hand relating to your compasses. This is the last Celestial solution in this "epic link" relating to bearings or sextant angles…By this time.. if you at all applied some of the techniques…you might begin to realize that the information is not as valuable on a one time basis as if employed on a regular basis to establish a trend… that all is well and predictable. We are not so much looking for definitive answers but rate of change.
Sunrise Sunset
This is similar, to Meridian Transit except in LAN, we needed to correct only for longitude… Here we correct for our latitude as well. Take a look at your work sheet. By this time if you have done your homework, no explanation is necessary except for one. In your daily sheets, on the right hand side of the second page, you will see the times of sunrise and sunset for the different latitudes. Your first correction starts with an Interpolation. Just plug the numbers in on the work sheet…You should have it all figured out. Fill in just the way I suggest… We are looking for sunrise. Lat. 37-15N Lon. 116-23’W
Interpolation:(Time) 0456@35N
0442@40N
d= -14m
increment X 135m
divide interval 300mts
correction -6.3m
corrected time 0450
Nearest Meridian 120-00W
DR Long 116-23W
Difference 3-37
From Arc Tables: 3 degrees = 12 minutes of time
37 mts of arc = 2 minutes 28 seconds of time
0450 - 14 =0436 The event of sunrise for that day at aforementioned position occurs at 0436 Standard Meridian Time.
END "Keep on Looking Up ".
Godspeed
Goodsailing
