Getting Started in Celestial Navigation (The Noon Sight for Latitude)
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- Опубликовано: 28 сен 2024
- This video is part 2 of the "Getting Started in Celestial Navigation" video series.
Part 2 of "Getting Started in Celestial Navigation," (The Noon Sight) describes the process of finding latitude at noon from the sun, and introduces the concepts of geographic position, zenith distance, and declination. It also briefly introduces the Nautical Almanac, and features three example problems.
Here are some additional resources pertaining to this lesson:
1. Wikipedia "Geographic Position" - en.wikipedia.or...
2. Wikipedia "Zenith" - en.wikipedia.or...
3. Wikipedia "Equinox" - en.wikipedia.or...
4. Wikipedia "Declination" - en.wikipedia.or...
5. Wikipedia "Lahaina Noon" - en.wikipedia.or...
6. Local Apparent Noon - oceannavigation...
7. The Bridge Refresher Guidebook (with a lesson on local apparent noon) - 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.
Hi Chris,
What a fantastic job you have done with this series of videos.
I learnt celestial navigation back in the 80's, and despite GPS ,still carry two sextants on my yacht.
I do pull them out regularly to keep in pracice and have found your series of videos to be very helpfull.
thanks Charles
Ty
Magnificent presentation. I am so grateful you did not let that melon go to waste!
In the first of the three general cases, where you & the Sun are in opposite hemispheres, it seems to me that the formula, Latitude = Zenith Distance - Declination, only works if you ignore the signs (plus for north, minus for south) for latitude and declination. You must use only their absolute values.
Thank you so much. I just started my ASA 117, Basic Celestial Endorsement course. Your videos are incredibly helpful. Thank you so much!
Good luck in your course!
Great video! You keep it interesting with the changing scenery so that the viewer remains engaged. Celestial Navigation is best learned ad a practical application and most torturous when studied in the classroom.
I wish they would teach this in public school Math class! Instead we learned solutions to impractical problems that I have never used once in my life!
@Jack Stone They do in fact teach us about latitude, longitude, how to calculate that and the relative position of the sun. Using a sextant is just applying these concepts that we learned from school already. Or else school should teach us to use every single object and task we would use in our lives?
My Public Schools taught us a bit of this stuff in the 6th grade!
I'm firmly convinced we got a much better general Education back then, them most College kids do today!
I'm constantly meeting recent University "Graduates" that have no idea why "the Moon changes it's shape during the month"!!!!!
Yes, I'm not lying.
@@robinj.9329 there are plenty of those people in the flat earth society. It's aggravating
A very nice tutorial, thanks for sharing about the celestial navigation.
just watched your video series nicely done . have just started looking at celestial navigation found it both interesting and very informative
Best explanation I have seen in use sextant for navigation . .
Hi man. I just watched your video and I have to say this it was so useful and So damn cool and also was So interesting I had No idea about the sextant or about the celestial navigation, after seeing your two videos I now know about it and I won't say I am a master in it by now, but I'll improve Myself by watching your upcoming videos. Thanks Sir. Again, you are awesome!
As a private pilot I can appreciate the importance of navigation. That and curiosity brought me to your videos, which are very clear about everything but this; Is there math that compensates for the variable heights that the sextant measurements can be taken from? Even if the different heights people can be is too small to notice, what about being on an aircraft carrier vs a clamming skiff, of even just on the bow of a tugboat vs the wheelhouse?
There has to be some kind of math for to preset on the sextant for how many feet above sea level you see the celestial body from, unless its too small of an increment to matter.
------EDIT-----
I spoke too soon lol, next episode covers it
Qq
Thanks for great down to earth video on a difficult to understand subject. I was wondering if you are shooting at local noon time do you use the declination for UT 12 or in my case 17 as I am in Eastern Time Zone of US which is 5 hours behind. Pretty sure is 12 as you show in this video but wanted to clarify.
Hi Jeff, Great question. When shooting a noon sight, the exact timing is not critical. Since declination changes so slowly, to be honest it doesn't really matter if you are off a bit. However, to be as close to precise as possible, you want to use the declination for the GMT (or UT) time of the sight. So if you see the sun at it's highest point at 1220 local time (on the east coast in winter), you would need to use a declination for 1720 GMT. That said, you could easily just use the 1700 time, since the difference is so small. As this video was an introduction, we simplified tasks as much as possible to illustrate principles. In later videos, we get more precise with time in the Nautical Almanac, but it sounds like you've got the principles down pretty well, so the short answer is: yes, you need to convert to UT! :) Thanks for asking, good luck!
Great stuff.Keep it up....I want to know if you can use the above formula to calculate your latitude at any given time of the day except the LAN....Help me on that
Not necessarily your latitude, but you can use the sun (or any body) any time to determine a line of position, If you do that twice, you have your latitude and longitude. It is a different formula though - noon is a special case. Thanks!
@@NavigationTraining Thanks so much for great insight, i now see the point...i have even tried some problems on the universal plotter
Clear and fun teaching, thanks!
Chris, if I wanted to take a noon sight at my LAN how do I calculate LAN if I know my longitude? Would it be as simple as converting my longitude or arc into time and adding that time to UT if I'm West of the prime meridian? If I wanted to be super precise, do I need to account for Equation of time in the almanac?
Thanks!
I think I missed something important, and watching the video again I don't think I gleaned it. When you get to the drawing in the examples;
Since I'm finding latitude, I don't have that yet. (if |lat| < |dec| then I'm closer but IDK lat...)
I know the declination distance being positive (N) means the sun is in the northern hemisphere,
but the zenith, the way you've calculated is always positive 90 - ($sextant_reading < 90).
How can I possibly determine whether the sun or I are closer to the equator (by angular measurement; I know the sun is 8 light-minutes away, thanks) Just realized this is only a problem in the examples in the next video (IRL I can tell by which way I'm facing while measuring the sun) (EX2 in the Precision video bit me)
What model of sextant do you use? Anything you would recommend?
Hi alex, I have an Astra 3B, but have used many different varieties and almost anything will do the job, even the less expensive plastic sextants. Don't feel like you need to spend lots of money on a sextant if you are just starting out. Hope that helps! -Chris
Brilliantly explained
Spot on , I subscribed to the channel😊
For the last example, how do you determine that the sun is further north of you? Zenith distance means the distance of you from the body right? Can you explain why latitude can't be declination plus zenith distance?
Hi Abdul - for the third example, we imagined a scenario where you are in the northern hemisphere but the sun is to your north (e.g. you are in the same hemisphere). You could determine this by using an almanac to find the location of the sun compared to you on a given date.
Once you determine which situation you are in, then you can set up the formula. In this case, the latitude is equal to the declination of the sun minus the zenith distance. If you set up the formula as declination plus zenith distance, you would end up too far north.
I find that drawing the picture of each situation helps it make sense for me! Hope that helps and thanks for your question. - Chris
Hi Chris. Thanks for the reply. What I mean from my previous question was, what is the purpose of calculating our latitude? It's because we don't have the GPS right? If that is the case, then I would know the latitude of the sun (the declination) from the almanac but I wouldn't know my exact latitude since I'm not sure of my position. Then how can I know if the sun is north or south of me? Say if the sun and me are both in the same hemisphere. My apologies of I got the whole purpose of this wrong.
No problem Abdul, its a good question. You are correct stating that you won't know your latitude ahead of time. So I would answer you in two ways:
First case: you are on a ship and navigating. In that case you have a dead reckoning position (a rough idea of where you are). So you don't need to know your exact latitude - just whether the sun is north or south of you. Since the sun changes declination from 21.5 South to 21.5 North over the course of the year, it would be very rare for you to be at the same latitude as the sun - your DR position should give you the answer. However if you ARE very close to the latitude of the sun, you could do the problem both ways (i.e. one for sun north, one for sun south) and hopefully the correct answer would be apparent based on your previously charted position.
Second case: you have no idea where you are. First of all, that stinks :) But seriously, again it would be rare for the sun to be so close to your position that you couldn't determine the case. One way to do it would be to put a stick in the ground (or on the deck of the boat) and every hour put a pencil mark on the ground wherever the shadow is. Then, after the sun passes you at noon, compare the marks to your compass to determine whether it passed you north or south. Simultaneously, you record sextant measurements and do the calculations for whichever case you determine.
It's a good question and I know your mind is working in the right direction - but if you want to talk further you can certainly email me at chris.d.nolan(at)gmail.com and maybe we can do a chat or call or something. If you do write, let me know roughly where you live and I can do some examples for your homeport based on the seasons to help you out.
Hope that helps!
-Chris
Ahhh. I kind of get it now. I was just thinking that maybe for the second scenario, at noon, since the sun is on your meridian, it could only be north or south of you. So if you were to face north at noon and your shadow is forward of you that would mean that the sun is south? and if your shadow is behind you that would mean that the sun is north? Am not sure if I'm getting this right. Anyway, thanks for your help Chris. It's a great series your making. Keep it up!
Abdul Hafiz bin Sabani You've got it exactly, Abdul. Make note of where the sun is at your home every couple weeks and you should really see a noticeable change, it will help the point sink in perhaps. Take care, -Chris
best of the best
Very interesting. Thanks a lot. Keep on good job :)
So how do you keep your food fresh in between islands?
Hi Shwartz, our sabbatical is done now, but when we were sailing we used a Yeti style cooler which kept ice for about 4 days. Otherwise it was a lot of fresh and not chilled food from the market. Good luck!
where did you get 89*60' from? i've not seen that anywhere else in like RYA books an' that
Hi Rory, cool picture. Sorry if I wasn't clear...90 degrees would be equal to 89 degrees and 60 minutes, so it's just a math (maths?) trick to help me avoid having to subtract from 00 or use a calculator. So to be correct, it is 90 minus the value, I just used a shortcut. Hope that helps!
Ooooh i geddit. Realise now it was a bit of a dumb question
there is no way of knowing the exact time the sun will be at your zenith. you can know that the time of your meridian passage but it does not tell the angle of where the sun would be.
Hello Red Devil - the time of your meridian passage is the same as when the sun is at it's zenith for the day from your point of view. We're not looking for when the sun is at "our" zenith, but when it reaches its own highest point in the sky for the day. And at that point, you use a sextant to measure its altitude (angle in your words). -Chris
66 years old
What do you do if pirates stole your sextant and your compass... because, well, they're pirates?
I would negotiate with the pirates. I prefer to do it "aye to aye" :)
Flat earthers use celestial navigation to prove the earth is flat.
How to tackle them
celestial navigation requires the earth to be a sphere. It required spherical trignometry and the starlight to be parallel. Dont worry about flerfs they defeat themselves.
yeah trig throws that out the window.
In short : Buy A GPS . It is terribly more simple to have your position with a GPS
The US Navy is teaching astro navigation again, I wonder why. Apart from being independent of the GPS or other satellite systems, it is a fascinating and practical combination of astronomy and trigonometry.
@@karhukivi GPS signal are weak and easy to jam and they do not cross areas where bombs have previously exploded due to high air ionization
sorry to break it to you, we don't live on a spinning ball flying through nothingness .. other than that, good vid
Stick to golf.
@@marcg1686 no I'm a Christian. I'll stick to the truth
@@maxxsee Whatever.
Thank you for the input; this is a basic/introductory celestial navigation series. Interpolation for declination is covered in episode 3. v corrections for GHA of bodies will be covered in future episodes. I've found it easiest to introduce one concept at a time to avoid people giving up on learning.
For the latitude calculation you don't need 3 different formulas or any drawings, you just need to sign everything properly (positive for north, negative for south) and always do an addition. For instance if the Sun-zenith angle is 41° and the Sun's declination is -17° then you get a latitude of 41° + -17° = 24°. Your Sun-zenith angle is of course negative only if you have to point your sextant to the North.
Thank you for the simplicity!
Thank God for RUclips
God has nothing to do with it... thank science, tech and people!
Hi, Thanks for watching - Zenith Distance is the distance from the spot right over your head (90 degrees) to the object. 90 degrees is the same as 89deg 60min, and I just use that because it makes mental maths easier. Sorry if it was confusing!
It’s a handy trick.
At this point in my life I am nearly 100% certain I will never find myself in a situation in which I will need to rely on a sextant for any purpose whatsoever. But, having said that, I've always been fascinated by them and wondered how they work and how to use one.
Your video series is clear, simple, and quite informative.
Big mahaloz!
Celestial navigation gives your true location where you are at. GPS will will give only to get back. GPS does not show correct latitude and longitude.
Thanks Oski!
I like this intuitive, conceptual explanation to gain understanding of the numbers. It's possible to get overwhelmed in details of dip correction, d correction, etc without clearly understanding the general principles.
Seems to me from your introductory remarks that you are referring to the practice of taking sightings of the Sun at local apparent noon to determine its altitude (and hence zenith distance). If so, then the term "noon site" in the video title is misspelled. It is not a site (i.e. a location or area), it should be spelled "sight", or more correctly, it should be called a noon sighting. Otherwise, a good introductory lesson. Thanks.
Great video, thank you so much for explaining it slowly and in an easy way!
Hi Chris what is the sextan you are using for this série ?
Very instructive ,thank you
Hello this is Astra IIIB. Any sextant will do the job!
Your explanation and examples are awesome. Thank you for posting these videos.
Imagine being an English midshipman in the late 1700s. The sailing master is trying to teach you this. If you screw it up, you get sent to the grating for a date with the cat o'nine tails.
David Barrie #author 'enthralling' #book #Sextant The Halli Casser-Jayne show 5/28 3 pm ET #sailing #invention
bit.ly/U4EEMd
What an awesome video, great explanation and kept me interested.
Something that has been puzzling me for years. When taking the meridian altitude, why is it not possible to make a note of the time and then translate that into degrees and minutes which should give you the longitude. For example, presuming noon that day had been 1200 at Greenwich, and the time of your noon sight was 1400, would that not mean that your longitude was 2 hours of arc i.e. 30 degrees W?
Exactly the right thought process as far as the math and you are correct. The two factors to note: first, historically clocks were not accurate enough to precisely time the sight, and second, even now, noting the precise moment of noon is difficult.
To the first point: this is a historical sight because it doesn't rely on time - since it is the one time of day the trigonometry is easy, old time sailors used it as their main celestial sight. So we still teach it because it serves as a good theoretical foundation and is still a valid sight.
Secondly, as the sun reaches its zenith, it "hovers" there for a few moments before clearly heading towards the horizon...since the sun "moves" across the surface of the sea at a rate of about 15 degrees per hour, or 1 mile every 4 seconds, it is rare for us to precisely time the sight enough to get within 15 miles of our actual longitude.
So - yes your process is right, and you can definitely do the math, especially if you want a rough longitude. But practically, most sailors use the noon sight for latitude and get longitude later in the afternoon or earlier in the morning.
Now, with all that said, if you want to precisely calculate longitude at noon, you can do it two ways: first you could take a bunch of sun sights close to noon (e.g before and after), plot the arc on graph paper, then you can easily "backwards" calculate when noon was, and use that value. The second method is to take a sight shortly before noon, leave the sextant set to that angle, and when the sun climbs and eventually returns to the same altitude just after noon, you can take the time interval between sights, divide it by two, and that is the time of noon!
Great question.
Chris Nolan Thanks for that Chris. Brilliant series of videos, well done
Appreciate reply. Now that that is clarified....I have one further question that is not simply explained. Have been reading and watching but not clicking in my mind. To calculate longitude you do what? LON = ?
Sorry if simple question but is confusing me.
No problem Jeff - the calculations used in this episode are only for latitude…they provide you with one "line of position." The easiest way to calculate longitude is shown in later videos, particularly in the "Going Further in Celestial Navigation" video series. There is a way to calculate longitude at noon, but it's fairly esoteric, but here is an article if you are interested in it: www.oceannavigator.com/November-December-2011/Noon-sight-longitude/
Hope that helps!
great video for noon sight! question... how do you know the position of the sun relative to your current position? obviously, this determines which of the 3 calculation methods you use. (i'm just learning, so please excuse me if this is a stupid question.)
Absolutely brilliant presentation, a real ‘Ahaaaaaa I get it now’ moment for me! Apart from the 90deg to 89deg60 trick.🤷♀️
LOL I had to build a rough sundial never know when sun is exact overhead. That's good teaching my navigator friend taught me to draw it each time too.... Thanks for another great video!
Great tutorial. I'm not a sailor but after watching a documentary about Ernest Shackleton sailing from elephant island to South Georgia Island in a dingy using a compass and a sextant, I wanted to learn how a sextant works. Thanks
Totally an inspirational story. Thanks for watching!
@@NavigationTraining The Shackleton story is an odd one. He assembled a bunch of sailors that weren't very experienced, and in a colossal blunder of planning got himself trapped within the Antarctic ice. Then, he made up for it by performing the most heroic survival and rescue trick of all time.
Sir, Excuse me, I have a question about this theoretically: What is the latitude of a place where the length of the day is 2/5 the length of the night if the sun's declination is 20 degrees 20 mins south?
thanks, brushing up on old skills. Lahaina noon is tomorrow here on Maui. I'm going out at noon and using my flagpole to find my latitude here in Haiku. thanks,
Superb sir... I need more help.. sir please elaborate the concept with more examples... 🙏🙏
Yes I plan to enter the Golden globe sail boat race .But my sextant navigation is primitive beginner. I want to be able to find zenith at night with out the horizon visible so I can Messer from zenith to the southern cross . How do I find zenith with a sextant .?
Did this in the Navy over 40 yrs ago, this is a nice refresher.
I'm with the rest - this is brilliantly done THANKS ! I share difficulty with ngojcam about where the sun is relative to equator although at my home 55*N. I reckon it is south of me most of the day - year round.Also I found it hard to see how the declination was raised from the tables. Maybe that all comes in the next videos.
I think I'm going to get a set of tables and practice! (but I did enquire and they are £30 GBP in Ireland - where's that Christmas list ??). Yesterday was vernal equinox so I made up a plane table and took a reading for zenith distance/latitude and got it to within 15 minutes. Plywood and welding goggles job.
Sounds like a cool construction project! Here's a quick explanation on the movements of the sun relative to the Earth, hopefully it helps out - the geographic position (GP) of the sun is the spot directly beneath the sun...if you were standing at that spot it would be directly overhead, super hot, and there would be minimal shadows. If you moved as fast as the sun over the Earth's surface, and it remained forever overhead for you, you would trace a spiral around the world, with your latitude slowly oscillating from about 23.5 South at December 21st to about 23.5 North on June 21. Then you'd turn around and go back south for the next six months. These points are the lines represented by the Tropic of Cancer and the Tropic of Capricorn and the Sun reaches them on the Solstices (head over to Stonehenge then for a wild party :). Now instead of following along with the sun, just plot the the Sun's noon position everyday for your location (whenever the sun crosses you, when is at its highest point in the sky in Ireland each day). From 21 November to 21 March, the sun's home is in the Southern Hemisphere, so your noon latitude is Lat = ZD - Declination. From 21 March to 21 November, the sun lives in the Northern Hemisphere (your hemisphere), so Lat = ZD + Declination. Just a reminder ZD is 90 minus sextant reading. Now as far as getting declination - it changes pretty slowly so its not really a critical thing. At the solstices it changes super slow, and it's at its fastest around now (the equinox). However, all things considered it's always pretty slow. So just pull out the declination of the sun from the Almanac for the nearest hour to your observation and you'll get pretty close (remember to use GMT). If you want to learn how to get the declination exactly right - later videos will cover that, but I am glad you are focusing on the big picture now! Thanks for writing and keep up the experimentation!
NavigationTraining
Got it !! That is one total answer !! I hope your employer appreciates that you gave up part of your sabbatical to teach us all. Maybe even grant you another leave, SOON.
I just added to the global credit bubble by ordering the almanac NP303 (1) from our local chart agency before my pay cheque arrives.
Really enjoyed the video. I must have missed something important, but why can't one measure the sun's altitude at any time of the day and use the tables to obtain the declination then, and then do the calculations?. I understand that wrist watch time is not exact as it gives you the same time over the width of the entire time zone, but wouldn't it be off by only a minute or two, i.e. a nautical mile or two? Your video stimulated me to buy a sextant and am looking forward to trying it out.
Thanks, Rob
Hi Rob, you can definitely use the sun at any time of day - however the calculations are more complex. Only at local noon does the math reduce to an easy addition problem you can do in your head. At other times of the day, in order to make the appropriate calculations, you need to use spherical trigonometry to get your answer. That sounds more impressive than it really is - in the end it is just looking up numbers in books and doing some addition, but there are more steps than the noon sight. Check out "Going Further in Celestial Navigation" to learn about using the sun at any time of day. You may also notice from a few comments in this thread that we've simplified this process slightly in order to teach a few key points. In later episodes we increase the complexity to the point where you can be exact in your calculations.
As far as time - the noon sight time is not super time-critical because the sun tends to hover at nearly the same altitude for a few moments (think of an amusement park "pirate ship" ride - where the ship reaches its highest point, hovers briefly, and then accelerates downward again). In math terms, local noon is an inflection point in the curve. So you have some wiggle room in the time, such that it won't make a huge difference. That is what made the noon sight so useful before the invention of the chronometer. However, at times other than noon, you must be much more precise (for the reasons mentioned above). In fact the sun "moves" about 1 nautical mile across the surface of the earth every 4 seconds. So your watch time should be as precise as possible. If you check out the "conversion of arc to time" pages in the nautical almanac towards the end, you can get a sense of how it works (e.g. 360 degrees = 1 day, 15 degrees = 1 hour, 1 degree = 4 min, 1 second = 4 miles etc).
Hope that helps and enjoy your new sextant! - Chris
Thanks much. For now, I plan to get comfortable with noon sighting as there's a lot to absorb, the further along in this course one ventures. i assume I can get my longitude, by knowing how many hours west or east I am from Greenwich and converting that to a longitude. My sexton manual also mentions an equation for time factor to further correct this.
On another note, if one takes a sighting on a star or planet, is their an equivalent time to a noon sighting, or does this involve the spherical trigonometry issues you mentioned?
Thanks,
Rob
lisarob5767 Thanks Rob - sounds like a plan! Noon sight is a great place to start. You can do something similar with Polaris, the north star, if you live in the northern hemisphere. Same as the noon sight there are a few simplifications you can make to get 95% of the way there, and then add details when you are comfortable with the process. But yes, I agree the sun at local noon is the best place to start! Good luck :)
Okay, mind blown at 1:27 because now I know how to sail the deep blue with nothing but the sextant and sky, and some ciphering. Fantastic! and Classic! Let's GO!
Thanks!
Beautifully explained! I've always wanted to know the basics of how you determine location w/ a Sextant (and how accurate one could be on the deck). This (and the preceding video) gave me what I was looking for in a nutshell. Thanks.
Thank you, thank you, thank you!!!
Great video, but i have a question. How will you name the Latitude? How will you know if it's North or South? Thanks!
Hi Marvin - we would just count on having a dead-reckoning position clearly in one of the two hemispheres and go from there (e.g. you have a pretty good idea based on your last position). However if you were right near the equator it would be tougher to determine so you'd need to pay careful attention to the math. Thanks for the question!
im color blind , just didn't work ,,watch at least 100 more times ,,,,yep
Nice video, learnt a lot, I feel like these were simpler times, 2013.
Sir, how do we know which hemisphere are we in? in order to mention in the diagram.
Hello, you should have a dead-reckoning (approximate) position from the previous day or something hopefully. If you are in a liferaft and have no idea where you are, you have bigger problems for sure! But hopefully you have an idea of where you approximately are. For instance "off the east coast of USA" = northern hemisphere, or "west of Chile" = southern hemisphere. Hope that helps!
@@NavigationTraining Thank you so much for the reply sir.
Excellent in every way. Just watch them over and over and it sinks in as you write it down, practice and review. Great way to learn. Skipper Pete - Hunter 36
Peter Bombar Thanks Peter - enjoy your sailboat, unfortunately I am stuck ashore for a while!
Not a stupid question at all. It depends on "roughly" where you are. Think about it this way - around Sep. 22 and Mar. 22, the sun is right on the equator. Around June 21 and Dec. 21 the sun is at latitude 23 and a half (North in June, South in Dec). Drawing a picture or graph can help. So unless you are close to those latitudes at that time, it should be no problem to determine which situation you are in. If you msg me with approx where on Earth you live I can explain more if you'd like.
What I'd you don't know the UTC time, such as the sailors hundreds of years ago who didn't have clocks or mechanical timepieces?
Hello, the benefit of the noon sight for latitude is that it doesn't require time. As long as you observe at the highest point in the sky for the day for the sun you are good to go. Knowing the approximate time and especially the date is needed for declination. But for the accuracy required it's not needed. Thanks!
Just love u man....
Could u explain y we prefer long by chron in morning and intercept in evening?
I live in the mountians dos it matter if i gona use a ridge
Laminated sheets illustrating each of the possible scenarios where you could fill in the values in grease pencil might be a handy aid. I am definitely a visual learner and your illustrations were a great help.
Great point!
You wrote on the book! I felt every milliseconds of it
well I think first you need to fix your sextant altitude to Ho.You can not substract directly your sextant altitutde from 90 degrees to zenith distance.Because there will be some errors like (parallax,Altitude,Tempreture and Pressure,Index error of the sextant and Dip error) before substacting you need to calculate them also.
Thanks Berke, as this is a basic course, I've chosen to present topics in the order I've found to be most effective for learning. All of the corrections you've mentioned are correct, and we account for them in later videos.
exactly I agree with you berke ;)
Dude chill he covers those things in later vids.
I love you man, this is amazing teaching
How far from the noon sight can you be before you run into problems with inaccuracy from not being on the same meridian as the sun? Since you don't know your exact longitude, isn't it hard to tell when the sun reaches its highest point in the sky?
+spelunkerd Hi Spelunkered, thanks for the question. The way you determine when the sun is on your longitude line is by measuring it's height for a few minutes around solar noon (either calculated or estimated). When it reaches its highest point - it is on your meridian and that is the time to make your observation. Thanks!
"When it reaches its highest point - it is on your meridian and that is the time to make your observation."
But how do you know it's at its highest? How do you know that if you wait a few minutes it won't get higher?
By looking throught the almanac you would know the time of meridian passage of the sun .
Love you eating the melon at the end... it really sets the stage. :D Nice videos, and thanks!
We use the same little circle method. Great Video. Well explained.
How do you know where to place the sun on the picture based on your numbers? How do I know to place the sun above or below the equator?
It depends on the time of the year. Summer in the Northern Hemisphere or summer in the Southern Hemisphere.
For a couple of centuries before the wide availability of accurate chronometers, THIS was about all the Celestia Navigation that any ships Captains knew and used. They would just obtain proper latitude of their destination via the Sun, then proceed in that direction untill land was sighted!
Even in the final days of the last great sailing ships, right up till the 1920's this was all many old time Skippers knew!!!
I am not sure if you could beat this into me but it sure is interesting
Where did you find the 1800? Thanks for the video
Hello, I have a question. How can you understand, in the second example, that you are on the North hemisphere and not in the South (lat=28° 25,6'). Also how can you understand, in the third example, that the Sun is Northern and not Southern than you (lat= 20° 15,4')? You are doing a great job, thanks and keep on!
Hi Skylandermeletis - for these problems, we assume you have a rough idea of where you are (for instance you are not in a liferaft). So you have been navigating for the past few days and should know whether you are in the northern or southern hemisphere. Likewise, regarding the sun - if you know the date, you can tell whether the sun is in the northern or southern hemisphere. If it is spring/summer in the north, the sun is in the northern hemisphere (e.g. the declination of the sun is north). Hope that helps! Thanks!
Chris Nolan Thank you so much, yes that helped, I thought the same but just to be sure. Keep up the good work, Greetings from Greece!
Very detail
nice video
What a great explanation, ours clear you understand everything very well, & one of the clearest ways that's evident is the ease with which you teach the material.
If you can't explain it simply, you don't understand it well enough. That's an Einstein paraphrase, I believe. And clearly you do understand it well enough. 😃
Just found your page, LOVE IT!
Love the fact that you are eating the melon. No waste!
At the equator every second is 80 feet . I think .
Hi Chris, thanks a lot for sharing this videos with us. I am learning how to use the sextant, the nautical tables ans do on and, your videos are amazing! However, one thing I couldn't get it yet is, how you determine if the sun is in the same hemisphere and if so, above or below your position? Tried to figure out from the values you're showing in the examples... but I couldn't get it sorted out yet.
Hi Pedro, thanks for the kind words. You have a good question, but I would say that if you are on a voyage and navigating by celestial navigation, you would generally have a dead reckoning position to start with. In other words you would have a rough idea of where you were at when you started. In the case of being lost a sea or something, you would have a harder time...but you might not also have a sextant. So on your typical trans-oceanic voyage, each day at noon you plot a position, so there is always some idea of where you are. Hope that helps! - Chris
Thanks for replying Chris! I think I understood your answer... I mean, what you're saying is that, by looking at the last position from DR, the new Latitude reading should not be something totally different. When I asked you the question, was basically trying to understand which formula to use, i.e., Lat=Zd-Dec or Lat=Zd+Dec or Lat=Dec-Zd, which depends on the geographic position of the sun (in this case) in relation to your own position. But I guess, like I mentioned, if I don't know exactly which one to use, I can use all and see which is the one where the Latitude is closer the the last DR position. I guess there is a much more scientific way do know that... but I think this will work for me.
Fantastic, such a clear explanation; thanks very much.
Glad it was helpful!
Thanks
Clarification: adding the arc time to noon UT.
"Meridian Altitude" here in Canada, , ya
I loved these, "Rock that Sextant", It got my FRV Ship to Hawaii 4 times, well not by sextant sites, but it is always fun and peace of mind in case your GPSs go out.
Does not the Nautical Almanac repeat every 5 years? IOW would not a set of five in succession be all you need?
An excellent video.
Sticking toothpicks in a melon is brilliant.
Wish you had taught me maths in school.
"We are directly under the Sun... ...now!"
You're 100% right - I totally messed that up! Good catch. I think I must have been thinking of the website "Noonsite" for sailors. Also you are correct regarding the signs of lat/dec. If using a calculator or computer program, you'll need absolute value. Thanks for watching!
Is this video made in Saint-Pierre, Martinique?
Yes it is! Well spotted.
Hi! I am no sailor but just a little curious, and I wanted to learn more about sextants and I found your videos. This was very informative and I thank you for that, but I'm not sure to understand how you find where the sun is, in relation to you. What makes you say it is in the same hemisphere or not? Anyway, great video!
I think you'd do that by getting a sextant reading of the sun and referring to the almanac, but I don't know how you can tell where your location is without help from GPS or landmarks.
I will get there , soon , hopefully lol .
I have a question, kinda similar to Skylandermeletis but still different. How do you know where around the "sun axis" you are when you take measurements? The declination of the sun is given and the ZD is given, but the ZD is actually a radius that forms a circle around the "sun axis" right? Any observer on that circle will have the same ZD and declination. What am I missing here? How can you tell which of those 3 situations you should calculate with?
Hi M Tieleman - while it is true the ZD is a radius, at local noon the sun is by definition either north or south of you (highest point in the sky for the day). The sun is passing your meridian. So the question of which situation is solved by knowing the general geography or using your dead reckoning track. For instance if you are in Boston in summer, the sun is always south of you, and since it is summer, the sun is in the northern hemisphere. If you are in Sydney in (local) summer - the sun is always north of you and since it is (local) summer, the sun is in the southern hemisphere. If you are in the tropics, it gets trickier, and you have to rely on your DR position (e.g. you know where you were yesterday, or the day before, and you know you are traveling a certain speed in a certain direction). I've never run into a case where I couldn't determine the situation based on the season, my approximate location, and my DR track. I think its important to note that this isn't liferaft survival navigation, but rather what a yachtsman or merchant ship might use...you are going to know your DR position within half a degree, and the celestial solution is for a refined position (or more commonly today, for enjoyment). Hope that helps, let me know if unclear! Thanks!