Celestial Navigation: Sextant Basics
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- Опубликовано: 1 июл 2024
- Description of the celestial navigation sextant components and how it works; adjusting mirrors; selecting sun shades; determining index error; and shooting the sun by Captain Tom Tursi, a USCG Licensed Ocean Master with over 60,000 miles of blue water ocean sailing using celestial navigation.
From a Master to another Master.
Congratulations for such a complete and easy to understand explanation about the use and ajustment of a sextant.
In 1972 I was a Ch. Off. In a vessel that was delivered in Taiwan, for scrap. The Captain offered me the "substitute" sextant we had on board. It was one very heavy, with the structure as a rectangular grid, but has to additional itens, wich provided very accurate readings:
- in the micrometer had a Nonium Scale, to read 10th of minutes.
- and together with the shades had a astigmatic lens to "transform" the stars image (one light point) into a line, to better align with the horizon line.
Special salute to you Sir, with my best vows of
Fine weather, smooth seas and clear horizon
in the years to come.
A very good teacher ..No nonsense ..To the point.. a few seconds of space for a person to think.. Thanks you..
A few seconds isn't enough
Very well done! I have no personal experience with nor ambition to ever need to use celestial navigation (my marine life is limited to canoeing rivers), but have have always had a pure curiosity about the workings of this tool. You have an incredible gift (and obviously much experience) for conveying knowledge on these things, not limited only on how to use them, but also imparting an underlying grasp of their complexity and why they function as they do. Demonstrating how to not only recognize, but also utilize the more sensitive properties of a tool is no simple task in any field. You sir, are an incredible teacher. Thank you!
Good timing speed for the content. For me it is very helpful regarding the practical usage of the sextant.
The video is 8y old and still up to date. Well done and thank you for your efforts
Thank you Sir for that excellent demonstration of using the sextant. I’m 63 and I finally got to see it being used properly.
Thats the best explanation I have heard yet.
Thanks for that Skipper. It is, how one of the other writers here put it, the way teaching should be done. Just great.
Best explanation I ever saw. Thank you so much.
Thank you for demystifying that beautiful looking piece of mechanism that has alway fascinated me. Really appreciate you sharing your knowledge. Love this part of YT.
Best teacher I’ve come across! Thank you, Captain Tom!
Very good no-nonsense introduction to the basic techniques involved in using a sextant for sun sightings. I find all of the videos from Maryland School of Sailing to be really clear and on point.
I decided to learn how to use a Sexton after watching the movie "Longitude" about John Harrison who struggled to make sailing safer for all. You have made it easier for me, Thanks!
I keep enjoying your clips / videos ... good teacher, nice, friendly and very calm ;-) Greetings from Germany
Awesome! a complete free class by a competent instructor.
Capt. 👍🏻Nice, very well explained. Great thanks.😍
Thank you. I learned more in 36min on practical sextant handling than ALL the other 'how to' videos I've watched. Again. Thank You.
Great over all explanation. The rocking the sextant tip at the end is quite valuable.
Thank you very much Mr Tursi. Your explanation on how to use the sextant was magnificent. Great help.
This is learning and is a great way to learn from a Ocean Master. Thank You Sir.
I had to take my brain out and stuff this presentation in it. I'm glad I'm too old to make these types of calculations. I grew up with computers, IBM Mainframes. in my back pocket. The information was valuable, and I understood some of it. I'll save the video and watch it again.
Thanks for taking the time to make this video. I'm a beginner and I was really confused before I watched this. It was really helpful.
Great video and I really liked all the details needed for accurate reading.
Thanks for the video. It’s the best I have seen on the basics of the Sextant.
It's nice to know that someone is out there who knows what he's talking about and knows how to explain it so everyone can understand it. I didn't know anything about sextant use until I watched this video and now I think I'm ready to actually use one with confidence. But I'd probably get lost at sea anyway unless I got some serious training.
Not bad for 36 minutes. Well, not really. Make that 108 minutes because I liked it so much I watched it 3 times.
My only complaint is that he didn't tell us what we get. Results. Capt should have explained to the new folks that after all these adjustments. After all these fine tuning points/ After all the methods and swinging. After all the calculations - what the heck do we get? Besides frustrated and put the sextant back in the box. We get a LOP "Line of position" from the sun. If you "shoot" three stars - you would have three separate times and three separate LOP's Where those lines intersect is our calculated position on the sea. People don't have to understand how TO DO all that in the beginning - however - at least explain what they are working towards. Overall, good job Captain for explaining the basic sextant.
We have another video here titled "Celestial Navigation at Sea" that explains what you do with this information... T
Excellent. Clear and wholly informative. Thank you!
Thank you! Great tutorial on the basics of marine sextant usage! 🌅
This is how good instruction sounds like. Excellent Tom....
Thank you cpt, for sharing, it's so interesting to learn how navigation works, when all else fails. I was used to satellite navigation all my youth. Celestial navigation as I have learned on the uss intrepid is still in use today, so that even in case of a failure of satellite navigation, the seamen will still know where they are.
very good video! i just purchased an Astra IIIB used and can't wait to get started taking noon sights. thank you for this great information on sextants!
Thanks for the detailed tutorial. Excellent 👍
Thank you for teaching....regards from Spain.
Wonderful intro. So happy to have found you and the school. Will definitely be following up with some formal training.
this is how tutor should be awesome sir kudos to ur teaching sir..
That, Is how a subject should be taught! Very well done!
Thanx for a gr8 course : impressive to hear a master\expert at his craft 🎯🍺📐🚀
Thank you for your time and sharing your knowledge. 👍 😊 ⛵⛵
very good class! It makes a good introduction to celestial navigation.
It was a great explanation Captain Tursi. It was really a great job. Congratulation.
very well taught by capt tursi.sheer professional sir.thanx a tonns capt tursi.
Excellent instructive presentation. Thoroughly enjoyed it.
Terrific presentation, thank you.
Thanks for the very good step by step explanation.
Brilliant tutorial!, thank you Sir,best on the Internet,(and laughed at the Simpson episode clock intervals..)!!
You are an excellent teacher
Thank you Capt. Tursi
Enjoyed the tutorial, will get a pocket sextant for my piper a/c in case of power loss. I will look for a source for tables.
Very good explanation, thank you a lot!
Thanks Captain....excellent information...
Excellent video,thank you very much.
Can't wait to see it in action next month!!
Thanks for your help in explaining the sextant and other navigational topics! If I could afford to attend your school I would!
Excellent tutorial on how to use a Sextant for celestial sights. A good refresher for me. I also learnt a new trick, using the fingers of your left hand to steady your left hand when adjusting the index arm/micrometer by touching the wrist of your right arm with the extended fingers of your left hand. Thanks for sharing.
that was awesome....made it so clear..thanks
Well narrated and easily followed.
thank you sir i really liked explanation one of the best explanation till now about basics of sextant.
Fantastic explanation!
Thc
Carry on 😅
Class captain..
Soft & Simple explanation..
very useful..
but still all sailors R having that 10$ Casio Watch..
proud to be Sailor Sir..
please notify me if u have anything useful knowledge..
Thank you you are easy to follow and I am just a beginner.Your logic and speed makes everything stick
you got style man. well done! all d best...
Great instructions
Yeah...i really liked that. Good explanation...
like this video. watched all of it . thank you.
great video thanks man
Excellent training film thank you
Excellent simple explanation. Thanks
Great video. I will watch it a few times, at least!
Great video
excellent.
excellent!! thank you! :)
Very good video. Thanks for making and uploading it, sharing know how. I've got a question concerning the arc. The sextant used in this video obviously is a high quality one, with arc degrees up to 120, which seems to be pretty common from what I've seen on Internet. But I've also seen some that goes to 130 and 140 (as well as 110). Why those differences? What are the benefits (if any..) with a 130 or even 140 degrees scale on the arc?
A great question. As a Hydrographic surveyor and navigators yeoman, it was my job to maintain and teach others how to use and maintain sextants. Navigation sextants tend to have less degrees on the arc because it is difficult to get an accurate fix from a celestial body that is high in the sky. Sextants with more degrees on the arc are/were used by Hydrographic Surveyors and coastal navigators for taking horizontal sextant angles between three known points on land. Sextants with more degrees on the arc were known as Sounding or Survey Sextants. To keep the weight down they were stripped of shades and lighting. A team of five surveyors would work together to plot a vessels position and record the fix on an echo sounder trace. The routine went something like this; Standby to fix, ready on the left, ready on the right, fix. At this point, the echo sounder operator would press the fix button to mark exact time, fix number and depth on the echo trace. The left sextant operator would call out the horizontal angle between the first and middle mark, the right sextant operator would call out the angle between the middle and right mark ashore. The officer in charge (OIC) would plot the position using a three arm protractor and annotate the time beside the fix number. The OIC may at this point give the helmsman a new course to steer to maintain the planned track. Then this would be repeated minutes apart until an area was saturated with depth and position data. It wasn't so long ago this method of making charts was still in use, as late as the 1970's. As a vessel moved closer towards the coast the angles between the known objects ashore increased. Having more degrees on the arc made it possible to get closer to the shoreline if the known marks ashore where not able to be setup inland.
Thank you so much. Merci.
Sir, thank a lot.
Tom, how big does a lake have to be in order to be able to take a sighting with a sextant using the horizon? What's the distance minimum if we assume a height above water of, say, 10 feet?
Awesome explanation...I played with a sextant this weekend at a museum and I got a reading of 84 degrees. On this sextant there was no micrometer, so it is a very basic unit. I understand the different parameters and how they can affect my reading but if I just wanted to keep it very simple and not worry about calculation errors, can you help me understand? At the museum they had a sun painted on the about 15' up and they had a horizon line about 6' off the floor. If I have the 84 degrees and let's say it is 2:00PM on the dot, at sea level, where do I go from there? I would like to progress to where I can move the sun to help me understand this process of navigation. Thanks for your thoughts and help.
From 26:30... Blew my mind.
Superb explanation Sir--- I want to know how I can I use sextant to measure a distance of roughly 1100 ft. Could u please guide. Thanks
zeroing the mirrors reminds me of learning how to focus an image with my Leica. I imagine it's the same principal, err principle.
So, as a complete neophyte here, so forgive the silly questions, the business of mirror adjustment (that starts around the 12:00 mark), is that something that's done every time you use the sextant? Do you do it just once to set up a new sextant? Or do you simply need to check the alignment before using the sextant? Thanks in advance.
It is a good idea to do the checks prior to taking a set of sights. Often there will be no need to adjust much, so it will not take long to check. Having a well adjusted sextant will help you obtain accurate position lines.
Hi,
Nice video, thanks.
I've never used a sextant nor am I a mariner but just a detail about horizon mirror tuning :
you tell horizon mirror has to be set up by looking at the horizon.
I've seen in another video in which the guy set it up by looking at a star, not the horizon and, after that, at sea, IF the horizon mirror is properly set up, there must be a difference when you look at the horizon because you are most likely to be a few meters above the sea level : this is expected and this is the correction used by mariners (in general, a few minutes of a degree).
Am I wrong ?
+benoitdeg01 As pointed out in the video, you can also adjust the horizon mirror side error by sighting on a star. Either method works, but the result is verified by rocking the sextant while looking at the horizon and in this case there should be no splitting of the horizon if the setting is correct... Being a few meters above the water surface as you point out, is corrected for by the Dip correction, but that's a whole other discussion as explained in the video... MDS
interesting, by the way if you have not heard of this index error before, surveyors call it collamation error in their theodolites, but the rest of us just call it Parallax error, just as in an unfocused image on a rangefinder camera (ie. a Leica), where two images of the same object are seen in an optical system, just means a misalignment of optical components,UNLESS as i have said in camera rangefinder focus systems,aka an out of focus condition,just turn the focus ring, or in large format or Linhof camera rangefinders you adjust the Parallax knobs to the distance you are focusing, the optics are angled to compensate by the design of the rangefinder itself.
Hi Andy, in celestial navigation they use the term Index Error because there are additional parallax and horizontal parallax errors that must be factored in when taking sights of the various celestial bodies (sun, moon, planets & stars), when calculating a line of position. It would be very confusing, otherwise.
So, when selecting filters/screens, will you feel any damage that may be done? I mean, you'll know instantly if you need more of a filter, right?
How does blue ray come off through the split horizon mirror? Because in the video it seems as if the horizon mirror has an opaque rear side towards the oncoming blue ray, the one fitted with adjustment screws? Can anyone please explain?
The split horizon mirror covers the right half of your field of view... The horizon image (blue ray) comes past the left side of the horizon mirror in your field of view... T
What brand of sextant is being used? I've never seen a micrometer drum like that although I freely admit my sextant familiarity leaves a lot go be desired.
Freiberger
Good day Sir,
Before anything, I would like to thank you for uploading on the Internet all the videos about navigation. I have learned from them, they are very good.
There's a question I would like to ask if possible...I read a lot of materials about Celestial Navigation and there's one thing that I could not understand. They're saying like this: "We're taking bearings to the Star","We're taking bearings to the Pole Star" or whatever the celestial body is.
My question is how we could take bearings to one star using the alidade upon the Gyro repeater?? That star is supposed to be on the sky. Its not the same thing like taking bearing to a buoy or a beacon lying down on the horizon.
Please explain this to me. Its very very important to me.
Unfortunately, nobody have shown that to us. Just by the books but not practically which is way much important than reading.
Thank you very much for your kind support. You are the best.
When planning your star sights you will calculate using Almanacs and/or tables to get a bearing/azimuth and altitude of the star/s your want to use. This makes it easier and quicker to find the star you plan to use. If you have planned a good spread between stars, a bearing to the horizon is enough to help you find your star if you have the predicted altitude already set on the sextant.
At the end, you talk about taking the sight just as the sun is rising or setting. Wouldn't the sextant reading in ay case be 0-0?
Could one determine longitude from the sunrise or set times as one can at LAN?
Yes, the sextant altitude in this case would be zero, but the benefit of the zero altitude shot with the naked eye is that it can be done without a sextant, and there may be times when you want to do that
Gentlemen made note about the error on micrometer after adjusting the horizon (57.6 = 2.4).Are you then taking avvay the reading from final calulation as compensation? I did not see the final explanation on that one at the end as i vvould expect or he forget to mention it?
Yes, he forgot to mention it. The rule to help remember is, if the error is 'on the arc' take it off (subtract it). If the error is 'off the arc' add it on. They are opposites, which helps you remember. He did explain the difference of errors 'on' and 'off' the arc...... just forgot to mention the rule. So, the procedure is to note your index error (On or off the arc), take a sextant reading and then apply index error rule above. You must also apply the 'height of eye' (called dip), which is always subtracted from the sextant reading. There are height of eye tables in the Nautical Almanac. Once you have applied these two adjustments, you then must apply an altitude correction for the celestial body and time of year (altitude correction tables are also in the almanac). You now have the Observed Altitude (Ho).
I hope that helps.
Should I be careful about getting only the Freiberger sextant? There are many brass sextants on e-bay, but I don't want a decorative only/poorly working one. I've looked for sextant review vids on RUclips, and they are few and far between. In fact, this is the only one.
Good input Robert. There are many "fake but shiny NAV items that looks good but are not accurate. Also, knowing that GPS units for the ocean are different that those for land navigation. Knowing the Marine radios are different than CB radios...you brought up a great point.
What made somebody think of designing this instrument? Maybe watching the sun go over the sky
It's a more advanced version of a nautical navigation device called a backstaff. Which served a similar function but was much cruder and bulkier.
There is also a French computerised "Sextant".
The sextant is the silver spike to these flat earth vampires!
Sextants seem to be loved by both sides of the FE vs Globe debate.
Just a really cool tool.
You must be American.
Yes, I’m American, a retired aviator who spent his career at 38-41,000 feet, who’s circumnavigated the planet many times. . . Psst: it’s round!
@@joemeyer6876 I don't think that flat earth is a thing anywhere but America. I have had the personal pleasure of meeting one. Until that point in time I thought it was all just trolling.
use full stuff thanks a lot
You should adjust side error first before adjusting for index error
Abham Amin Is that critical ? Why does the instructor does it the other way around ?
How much does it cost?
"Perfectly perpendicular to the plane of the arc". Somebody needs to go back to junior high geometry class.
At 9:44, very important.
Now when you take the time does that mean the local time?
We convert all times to GMT for the calculations. It also helps to use the 24-hours clock method
whats is the sextant model / brand?
Freiberger Yacht Sextant
BASIC argument for C / Nav ZT/ZD/GMT
Why don't sextants have a gimble in/on the handle?
A bit late, I know, but here goes: (1) no need, the two mirrors seem to balance out a lot of the ship's movements, and (2) you need to swing the sextant from side to side like a pendulum to make the image of the sun (or moon, star, planet) move in a curve and the lowermost point is the one you make the measurement with.
@@karhukivi Thanks for the reply!🙂👍🏻
If you engage the trigger and change the degrees on the sextant to a new value, does the micrometer automatically reset to 0? Or do you first have to set it to zero before changing degrees?
No, the micrometer does not reset when you change the whole degrees with the trigger release. It stays where you last left it no matter what you do with the whole degrees... T
Great video do start with zero on the micrometer and index arm? Thanks Joe
link for the Sextant use in this video please
www.clauseninstrument.com/
There's a buble sextant that does not need a horison. Please can you tell me more?
The bubble sextant has been used in airplanes which don't usually rock and roll like a boat at sea. I've tried a bubble sextant on a boat and found that it was not nearly as effective as using the earth's horizon, so stick with the basics
***** Thanks, you make a valid point. The problem is that the horison is only visable in the day and stars at night, then there's cloud and weather conditions. G.P.S. could possibly fail, so I am interested in Sextant, but there seems so many limitations. I'm told there was once "DECA" that used radio beams. Sadly, that seems to have died the death. What would you recomend for a novice?
SonofBlackDefiance View our RUclips video titled "Celestial Navigation at Sea" and take our online Celestial Navigation course this winter where we cover the questions you ask very thoroughly. Also, send us an email at office@mdschool.com for additional guidance
+SonofBlackDefiance "I'm told there was once "DECA" that used radio beams." Yes, and also LORAN. GPS has pretty much replaced the other forms of radio navigation. It's fast, relatively simple, and very accurate. The advantage of celestial is that no one can hack the system, and power failure isn't an issue; the sun and stars aren't going anywhere, and if they do navigation will be the least of your worries. ;-)