Getting Started in Celestial Navigation (Accuracy and Precision)

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Getting Started in Celestial Navigation (Accuracy and Precision)

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Күн бұрын

This video is part 3 of the "Getting Started in Celestial Navigation" video series.
Part 3 of "Getting Started in Celestial Navigation," (Precision) describes the process of correcting a sextant reading to obtain a more accurate result based on the standard corrections of index error, height of eye, and main correction. It also refines the process of finding declination, and introduces Greenwich Hour Angle.
Here are some additional resources pertaining to this lesson:
1. Wikipedia "Geographic Position" - en.wikipedia.or...
2. Wikipedia "Sextant"
en.wikipedia.or...
3. Wikipedia "Declination" - en.wikipedia.or...
4. Wikipedia "Hour Angle"
en.wikipedia.or...
5. The Bridge Refresher Guidebook "Standard Sextant Corrections"
www.scribd.com/...
Navigation Materials
All example problems in this course use the 1981 Training Nautical Almanac and HO229 (there are three example problems in this lesson).
1. The 1981 Nautical Almanac
Hardcopy 1981 Training Nautical Almanac - www.amazon.com/...
Note you can also download for free or minimal price online by searching google, for example ebookpie.com/e.... You can download it from lapware.com if you pay the monthly fee for access. Sidenote - lapware is an amazing training tool!
2. HO229 - Sight Reduction Tables for Marine Navigation
Free download - msi.nga.mil/NGA...
3. Other materials of use
Free download of Bowditch (The American Practical Navigator) - msi.nga.mil/NGA...
USCG licensing website. This contains all the possible questions on USCG exams - www.uscg.mil/nm...
The book I used to learn celestial navigation myself, and I think one of the best celestial navigation books out there, is "Common Sense Celestial Navigation" by Hewitt Schlereth - www.amazon.com/...
Produced and presented by Christopher D. Nolan, USCG cutterman (8 years) and US merchant mariner (500 ton Oceans). Currently on sabbatical aboard S/V Navigator.

Пікірлер: 80

@PaperAndHomemadeGuns 8 жыл бұрын

I am a deck cadet , and also a maritime transportation student. These are so useful lectures for my Celestial Nav. exams. Thank you for doing these.

@laurenceholden 5 жыл бұрын

WOW! This is by far the best explanation, and so clearly step by step, that I have ever come across (and I have carefully studied, and restudied dozens of books on the subject as well as videos for 2 years now). Thank you, thank you. I go back to this series often.

@NavigationTraining 11 жыл бұрын

Great - thanks for watching! Good luck in your studies!

@arunkrishnans489 4 жыл бұрын

Sir, what is the purpose of finding geographic position of sun?

@nhojcam 11 жыл бұрын

just got my sextant today. astra IIIB. it's used, but it looks like its never even been on a boat. index error is almost nil. can't wait to use it! thank you for your videos. they are very helpful to a relative newbie like me.

@dandude02 7 жыл бұрын

hie Chris ...... ur vlog is very useful ....... specially for guys like me who is an aspiring second mate (merchant mariner)..............plz keep up the good work .

@knightnvy 11 жыл бұрын

Really enjoy the videos. I think you called every correction in degrees rather than in min

@mellowmood20 10 жыл бұрын

Hey Chris, I Just wanted to say thank you for creating this video series. I am a novice at celestial navigation, but am going on a sailing trip to the Bahamas soon and I hope to be able to apply some of the things you have taught.

@NavigationTraining 10 жыл бұрын

Awesome, enjoy the Bahamas. Check out Big Majors Spot in the Exumas if you can...they have swimming pigs that eat your dinner scraps - so fun!

@kennethhawthorn6618 6 жыл бұрын

mellowmood20 gr

@SVAdAstra 8 жыл бұрын

Thanks for a clear and concise course! I just followed your noon site instructions with a cheap plastic sextant and got within 3.1 nm of my true position on the first try! Well done!!

@chrisnolan825 8 жыл бұрын

+SVAdAstra Great job, shipmate! Glad to hear it came out so well!

@danielwalker5682 Жыл бұрын

Outstanding clarity and brevity. Thank-you.

@chrish6412 4 жыл бұрын

So I tried taking readings earlier this month using a training sextant. I was shooting from deck 9 or 10 depending on the direction of sail (North or south). Talking to the ship's Chief Engineer I was able to learn that the bridge (deck 8) was 30m above the water and deck 10 was 40m. Adding my eye's height (approimatly 5 ft) I came up with a Height of eye of approximately 116 - 137 ft above the water. Not finding those values in my version of the Almanac, I found the equation DIP = 0.97 * square root of Height above water. Using the SD for the sun, not the correction, I was still within 6 minutes of latitude every time (except day one in which I forgot to subtract it from 90 degrees and plotted us off the coast of Nova Scotia (after a days sail south of Miami.)

@NavigationTraining 4 жыл бұрын

Well done! That is a really high observation point!

@NavigationTraining 11 жыл бұрын

Good catch, thanks! I'll pay more attention to that in the next series :)

@NavigationTraining 11 жыл бұрын

Awesome, congratulations! Happy navigating!

@karhukivi 4 жыл бұрын

Not sure it's a good idea to start a course on celestial navigation with the sextant. Many people think that when you look through the sextant then - hey presto! - you know your position. Better to start with the notion of a position line or circle by looking up at a lighthouse whose height is known, and then working out the distance to it. Next, the "ground position" of a star or planet. Then the spherical triangle and the calculations in summary and finally the sextant altitude or angle. The precision and corrections can then be added once the basics have been grasped.

@NavigationTraining 4 жыл бұрын

Thanks for your opinions, totally a valid way to go! When I teach in the classroom, that's very similar to how I organize it. When I teach underway, especially with college kids, my order of operations (just like the series) is sextant, noon site (an easy win), how to make the noon site better (IC, DIP, Alt), and then give the theory - where most of them fall asleep haha. Thanks for your time and have a good day, sail safe!

@karhukivi 4 жыл бұрын

@@NavigationTraining Good to hear from you! I have shown kids a clinometer (good to only one degree) and a sighting compass and we do a very rough sunshot roundabout noon. They are astonished at how good a position that can give. Then I focus on those who showed real interest and we try doing the calculations for an angle and bearing of a planet to identify which one it is from the almanac. If they get that far, I then introduce the sextant. As I'm land-based, this part has to be done with a so-called artificial horizon, a bowl of cooking oil! Don't sail anymore but want to show how astro works and a purpose to maths and geometry. Stay safe!

@mgevirtz 4 жыл бұрын

Best episode yet!

@romankogalin7048 8 жыл бұрын

fantastic learning here nice job you doing

@jeanfrancis9892 8 жыл бұрын

Congrats ,Iam watching your videos in Brasil to review my capitan course,as far I ve meet others videos your are very nice....

@sailingketchstarship1965 4 жыл бұрын

You're a BOSS.

@CletusLeonardLee 10 жыл бұрын

At 3:27 minutes into the Precision video, you state that the index error is 2 degrees, when what you meant was 2 minutes.

@dinos8557 8 жыл бұрын

Chris, thank you for posting these videos. I have no need for these calculations but watched them because I enjoy learning new things. I assume the long (GHA). calculation starting at 7:28 in your video is also taken at the noon shot, the sun directly at the apex of its observed arc? This would have the sun on your longitude, knowing GMT the almanac provides position and local time has no bearing on these calculations.

@paulmchugh5924 3 жыл бұрын

Great as easy to follow as the Polaris Star considerate educative style leads the lost souls like me in the corrected direction

@gulfonetwo 10 жыл бұрын

PS digging the hot rod look on that Astra 3

@roslar1572 8 жыл бұрын

great info. I had to watch them few times. thx for posting it them.

@donjvalley 6 жыл бұрын

Excellent series!!! I'm retired, very new to sailing and need to learn this skill as autopilots always break, eventually...I didn't understand whether you ADD or SUBTRACT the MAIN CORRECTION --- please clarify for me....

@NavigationTraining 6 жыл бұрын

Hi Don, the main correction would be added for lower limb observations and subtracted for upper limb observations. So if you bring the sun to the horizon like in the video, with the lower limb on the horizon, you would always add the main correction. The main correction accounts for semi-diameter of the sun (the thickness from the lower limb to the center) and for atmospheric refraction. Good luck!

@powervoices 2 жыл бұрын

This is awesome

@stufirewalker 3 жыл бұрын

Hello Chris, brilliant series, thank you. Just wish the UK had beautiful sailing waters like where you shot the videos. I've come across a typo error at around 6 minutes 15secs into the video. You were describing the d number correction for 50 minutes, which came to +.8'. There's a screen shot showing the corrected declination of 18 29.4, should be 08 29.4 Regards Stu

@NavigationTraining 3 жыл бұрын

Thanks Stu, I hope to replace this series with a more modern one soon!

@nfaaudio8412 Жыл бұрын

This is so well explained. Just made it click!

@thracian 3 жыл бұрын

1:57 sunset getting green :p

@JC-yb3zb 8 жыл бұрын

I stumbled onto your video series by chance. I don't know anything about celestial navigation but it seems very interesting. I'm curious, it seems your sextant isn't secured (tethered) in any way, so how do keep from losing it overboard?

@NavigationTraining 8 жыл бұрын

+Jeff C Hi Jeff- thanks for bringing that up, it is always a good idea to secure your sextant with a wrist strap or neck harness if possible when underway. So far I've been lucky! But you are right I should use a tether. Thanks!

@sterlingtenor 8 жыл бұрын

Chris, I have been trying to learn celestial navigation for many years and your videos have finally made it easier to understand. I have been doing noon sights for latitude at my house on a lake. For three days straight, I keep getting a latitude that is 10 miles south of my actual location. I am wondering why, and suspect that it may be that my lake has a fetch of 4 miles to the horizon. Would this explain my error?

@NavigationTraining 8 жыл бұрын

+Sterling Williamson You bet! Two things: one is that your lake probably isn't at sea level, and two, as you say, the distance to the horizon is too short. The formula for distance to the horizon is 1.17 times the square root of your height above the surface. If you get a chance to practice at the ocean, I bet your results come out just fine....seems like you have the technique down pat!

@lousek1992 7 жыл бұрын

Many thanks for your awesome videos! Just two questions regarding DIP: 1. As far as I know, there are different sea levels e.g. in the pacific, atlantic or the mediterranean sea - how is this reflected in the nautical almanach? 2. What DIP do you use when using an artificial horizon at e.g. 500 metres above sea level (e.g. when in Switzerland)?

@kennethhawthorn6618 6 жыл бұрын

lousek1992 s

@Shellback1998 5 жыл бұрын

Confused about where you are getting the declaration, the date you have in your example is 4/10/1981, for that time I’m reading n8 deg 06.6, but I believe you grabbed the 11th day data. Would that be correct?

@gulfonetwo 10 жыл бұрын

What is your opinion on mechanically adjusting out the index error via the mirrors screws?

@NavigationTraining 10 жыл бұрын

Hey Nicholas - I thought I had responded to this, sorry if not…In general as long as the index error is fairly low (less than 5 minutes), I tend to leave it in the sextant…it becomes a known error that I can account for. I have another (old, non-flamed) sextant with a larger error that I do correct from time to time, but every time I do it kind of freaks me out a bit to be messing with it, don't want to strip the screws etc etc. So if I can avoid it I do! Thanks again, take it easy,

@SubwaySailorSailing 10 жыл бұрын

How do you know what time zone you are in if you are at sea?

@chrisnolan825 10 жыл бұрын

Good question - with 24 hours in the day and 24 time zones, and 360 degrees in a circle, each time zone is 15 degrees wide. So technically you would adjust your clocks as you move from zone to zone - however you can set the clock to anything convenient. For instance on some of my journeys we only adjust the clock at the beginning or end of the trip to avoid confusion on watches. So you just need to be aware of what time zone you are "observing." Standard meridians are located every 15 degrees outward from Greenwich. Hope that helps!

@MrAgentblues 10 жыл бұрын

Question? at Ex. # 1 the given date is april 10, 1981. but in your video at 5:17 you underlined the 11th day of gmt 1850h, declination of N 8 degrees and 28.7 minutes, i'm confused when i look at my own almanac at april 10 friday, 1981 at 1800 GMT and says N8 degrees and 06.6 minutes?

@NavigationTraining 10 жыл бұрын

Ok - thanks for letting me know…I bet I accidentally used the 2013 nautical almanac instead of the 1981. My mistake! Hopefully the process still made sense. Thanks again, good luck!

@MrAgentblues 10 жыл бұрын

of course it does. it really helps me to review all celestial stuff i study before and I do understand the concept for what am i doing. maraming salamat po! hehe

@NavigationTraining 10 жыл бұрын

Awesome - good luck! Ligtas sa paglalakbay (I think that's right :)

@MrLotengo 10 жыл бұрын

Chris, I could not tell from the video but is Dip constant for a given height of eye regardless of time or geographic location? If so, would it be possible to calibrate your sextant for that amount of Dip and have the index error cancel out the height of eye error? (assuming you take your readings with roughly the same height of eye each time)

@NavigationTraining 10 жыл бұрын

Hello sir, given your assumptions, I would say for your typical sighting from the same position on the boat you are fairly safe in assuming the same dip each time: dip does not vary with location or atmospherics. However index error can change (e.g. hot day swells the metal of the sextant), so it would not be safe to assume that IC and dip could be set to cancel each other out. For academic problems and to be strictly correct, you should refer to the dip table each time or you can also calculate the dip directly if you don't want to use the tables...Dip (minutes) = -1.76√Height of Eye (meters). Thanks for asking, great question!

@MrGotropic 8 жыл бұрын

Declination, Interpolate, GHA, LHA...... I'm in Heaven, .....

@jsytac 9 жыл бұрын

Should height of tide be calculated/considered when establishing Dip? How would you work this height out mid-ocean? Also, when the sextant angle is very near 90deg, how do you know if you are N or S of the sun?

@NavigationTraining 9 жыл бұрын

+Mc Egavas Hi - thanks for your questions. It isn't necessary to adjust for tides on the open ocean. Celestial navigation is used in open ocean environments where accuracy to 3nm is sufficient. As far as the sun being north or south of you - this is a good question and shows you understand the fundamentals. Unfortunately when the sun is nearly overhead, it is exceptionally difficult to measure - that is one of the problems of living in the tropics! Using your dead-reckoning latitude, compared to the declination of the sun for the day in question, you should be able to determine whether you are north or south of the sun. If it is so close you can't tell for sure, the sun will be so high in the sky that a measurement will be nearly impossible. Thanks for your questions good luck! Chris

@Ktrpilot 8 жыл бұрын

You Don't have to worry about height of tide when you are at sea and taking a sight, there will be some fluctuation in your height of eye anyway, especially if you are in a small boat or yacht due to the sea and swell and the rise and fall it's extremely rare that you would have no sea or swell to contend with shooting a sight even in the tropics. If you are getting positions within 2 NM accuracy it's more than good enough. With altitudes of close to 90 degrees your latitude at noon would be very close to the value of declination of the sun. If it was so close that you couldn't tell if you were north or south then it could be given that your latitude would be equal to the declination. Hope this helps.

@shipoperations8292 8 жыл бұрын

+Mc Egavas height of tide won't matter if you are floating. If you were on a fixed dock, yes, it would change the dip, but you'd already know where you were! The only time your sextant angle will be near 90 is when you are near the suns GP (it happened to me once) otherwise you can tell by the shadow pin on your compass.

@MrGotropic 8 жыл бұрын

I love Norries Tables, do you love Norries Tables ? do they still make Norries Tables ?

@tnuhodbns-captshekharchand1035 3 жыл бұрын

I love the Burton's Tables more..

@renzzamora8472 10 жыл бұрын

i have a problem, ive got 17*12.9 altitude at 1725H, whats next? because if i subtracted 90* to it to get the ZD it will be more complicated, my lat now is 28*24.8, and i dont know next, im confuse, and another how will i know if i was above the body, what i meant is the maximum dec of the sun was 23* and i was on the 43* lat without knowing, please help

@NavigationTraining 10 жыл бұрын

Dante D Hi Dante - if I am reading it right I think you are shooting the angle of the sun in the early evening...for this type of problem you need to measure the sun at local noon - when it is at its highest point in the sky, and when it is due south or north of you. It sounds like you live at about latitude 28 degrees and I will assume that is in the northern hemisphere. Right now the sun is about 18 degrees north in declination. So if you measured the sun tomorrow at it's highest point in the sky, it should be approximately 80 degrees high. So you would use 90 minus 80 to get a zenith distance of 10 degrees. Then, declination (18) plus zenith distance (10) equals latitude. As far as your question about north or south of you: If you live at 28 degrees north the sun will always be to your south, so you can practice at home knowing that is true. When you travel, you would need to have an idea of where on earth you are (a dead-reckoning position), then you would be able to tell easily, with very few exceptions, whether you are north or south of the sun. I hope that helps, if you would like to talk more you can email me at navigation.training.videos(at)gmail.com and maybe we can do a few more examples for your home! Good luck, - Chris

@renzzamora8472 10 жыл бұрын

thank you for your answer and all of your videos, it really helps me a lot, i don't really have an idea on celestial nav. but because of your videos i understand the basics and the other important parts that i need to know.

@daveocutter 10 жыл бұрын

Example 1, you added the ZN and Dec wrong. You put 17* 43.5' N. Its 17* 42.7' N

@NavigationTraining 10 жыл бұрын

Thanks for checking the math. Hopefully the process still made sense for you, my mistake! Thanks again and good luck!

@daveocutter 10 жыл бұрын

I watched all of your videos. I ordered my sextant and a copy of the Nautical Almanac. I cannot wait to try it out.

@toonamimaki285 5 жыл бұрын

Wow, this is the comment I was looking for and it was 5 years ago.

@Hallicj 10 жыл бұрын

David Barrie #author 'enthralling' #book #Sextant The Halli Casser-Jayne show 5/28 3 pm ET #sailing #invention bit.ly/U4EEMd

@Stellaferox 2 жыл бұрын

@4:33 min I think you are looking at april 11th and not april 10th

@donjvalley 6 жыл бұрын

I answered it myself, all I had to do was take another look at the math steps and see that Main Correction is added....Just old and slow....

@MrGotropic 8 жыл бұрын

Wow, guys your age would just be getting high and drinking and following their Waypoint on their GPS, not you, your doing it old school

@mrjp1819 5 жыл бұрын

This time you speak everything too fast ... If you do not know the almanac (like me) you do not understand what you are trying to explain at such a speed. You do not even see and understand what you are writing on the parpir. !