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.
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
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.
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.
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.
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.
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 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.
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!
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.
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.
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..
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.
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.
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
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?
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.
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.
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
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.
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.
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 RU-vid, 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.
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.
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
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 RU-vid 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. ;-)
I have a question. The sextant only works because the earth is a globe right? It wouldnt work on a flat earth, no flat earth model explains how a sextant works... Am i right?
All a sextant does is measure an angle. Measuring an angle on a flat earth or a globe is easy with a sextant. Celestial navigation only works on a sphere and would not work on a flat earth.
Ill make a 2nd post because i believe my first one wont pop up on your feed because i used a certain word. Look up your original comment to see it. Celestial navigation requires the earth to be a sphere to work. Celestial navigation works, therefore the earth is a sphere.
Sextons have measured angles over the ocean, the horizon is measured at 0 degrees, 0 minutes and that is a flat plane. The ocean is the bottom of the triangle and is required to be flat for the trig to work, otherwise it would be impossible for ships and planes to navigate over the ocean. NASA is a very well funded incorporated government bureaucracy. How did NASA sent Apollo to the moon and there if there was greenhouse roof in the way to stop the Apollo moon mission, if space is a vacuum, how do we have pressurized air without a greenhouse roof to contain and pressurize it? ~ When "science" is unquestionable and c∈ns0r∈d on social media then it's dogmatic "science" becomes a religion based on lies. The real science is being hidden from us, so they can scam us into non-existence.
@@martentrudeau6948 "the horizon is measured at 0 degrees, 0 minutes and that is a flat plane. The ocean is the bottom of the triangle and is required to be flat for the trig to work..." WRONG-O!!! There Marty. The rest of your comments really speaks volumes about why you should just be ignored. Sucks to be you.
In the early 15th century a Portuguese navigator, Pedro Reinel, is also credited with the first nautical chart that depicted latitudes in 1504. They used the Astrolabe an astronomical instrument to determine the position of celestial bodies. The Portuguese mapped the continents in the 1500s all with flat maps. The earth was mapped flat!
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
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.
@@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.
As some of you may already know, in any sort of Warfare at sea, an enemy could very easily "Jam" of scramble our GPS signals from the satellites. These birds are in orbit, thousands of miles away, and transmit at about 50-80 watts! That signal, at the Earths surface is very weak. The Chinese have already experimented with modes to block, scramble or make useless GPS signals over the entire south China Sea! Loran would have been much more difficult to jam! So, Celestial Navigation will remain a vital part of the Mariners "tool kit" for any foreseeable future!
