Sextant Tutorial: Taking Sights With A Sextant
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- เผยแพร่เมื่อ 2 มิ.ย. 2024
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---------ABOUT THE VIDEO---------
This video was originally uploaded to our other channel, Casual Navigation, back in 2018.
The sextant is one of the fundamental navigational instruments. Once you have mastered it, you can navigate the world without the need for a GPS.
This video is the third in a series which will teach you how the sextant works and how you can use it.
This video covers actually using the sextant to take sights.
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Consider subscribing to the channel if you are interested in any other topics we plan to cover:
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---------DISCLAIMER---------
This video should not be considered professional advice or education.
We try to make the content as accurate as possible, but the responsibility rests with the viewer to determine the full accuracy and reliability of the content.
Any action you take as a result of watching this video is strictly at your own risk. - บันเทิง
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I have had to teach this same "Introductory" material to many young sailors and boaters.
At first they are usually pretty confused. BUT; once the light has dawned!
"It is as if scales fall from their eyes!"
And NOTHING gives a teacher more satisfaction that getting an email from a young student, now thousands of miles away, excitedly telling the tale of his or her first Pacific crossing using only Sextant, compass, clock and charts!
wud you mind teaching one more student? I am confused still but trying hard to grasp the concept and it seems the specific calculations are so complex that NOBODY wants to show them cause it's too overwhelming... or maybe the calculations I don't understand are my problem... any advise to get that light in my eyes wud be AWESOME...
@@FlatOutHeroIt's been a year now, did you finally get the light? 😂 I really need ur response.
Great video. Now can you stop my boat from rocking so that I can actually do this?
If you use a sextant on a rocking boat you might be surprised to see that the double reflection from the mirrors seems to compensate for the boat's movement.
@@karhukivi Thanks, I was going to ask the same question. He alluded to this at the end but I wasn't sure
I can do this ... First open all seacocks, then cut the hoses in a few minutes you will have so much ballast she will not be rocking.
It’s not gps genius. It’s going to get you an accurate enough reading of your position to understand if you’re still on the right course or is god forbid someone needs to come looking for you if you’re gps fails. Do everyone a favor and just stay in the bay.
@@edg3123 From your comment it is clear that you have a very poor sense of humor, as you do not recognize it when it stares you in the face.
A couple of comments for these guys, this is only the start of finding a position, there is a lot of complicated maths and plotting after this. Due to bodies like the sun moving quickly in the sky timing is of the utmost importance, hence chronometers and noting the EXACT time you took the measurement, 4 seconds out is one mile of error. Using the sun we normally took a sight in the morning which gave you a position line at an angle, then at noon (not necessarily 1200) a different calculation gave you a Latitude at say 1230. If the first position line was at 0800 and your ship does 20 kts you move this to 1200 (80 miles along your course), you move the Latitude back 30 minutes (10 miles on reciprocal of course). These cross at a point and that is your 1200 position on local time. By far the most accurate positions were with stars, at my peak taking 8 stars (pre worked) I could have a position on the chart in 30 minutes, remember weather permitting we did this every day.
Can I ask you a serious question?
@@BertleMcGertle Of course
@@davidoldboy5425 I mean this with all sincerity. Have you heard of flat earth theory?
@@BertleMcGertle I appreciate your sincerity sir, and long long ago we we taught that the earth was an oblate spheroid, I forget the compression ratio. However what was of more concern was that the earth was pear shaped. I could never come to terms with this fact. However we soldiered on, occasionally dropping off the edge, where to this day vessels roam misty seas in a fourth dimension.
@@davidoldboy5425 thanks but I thought with all of your experience you'd give an answer based off of your observation not what you were told.
Thanks so much for this tutorial. Takes me back 50 years to the bridge of a submarine running on the surface in the Caribbean. A new junior officer needed to take a celestial fix to get qualified as an OOD. I was junior Quartermaster and had never used a sextant either. We took turns and got a successful location. Nice to know that I remembered it correctly.
Good tutorial but I'm still lost. What's the next step? Need a tutorial for dummies
one of the best tutorial of sextant, thank you sir for uploading this series..
Insterestingn. I carry the Aeronautical Rating of 'Master Navigator' from the USAF. I went through 'Navigator School' in the 1970s when Celestial Navigation was still a requirement. Our sextants were 'periscopic' and much simpler to use, actually - ASSUMING you had done your Pre-Computation correctly! Never understood how a Marine Sextant worked. Thanks for the overview. By-the-way, as I went off to phly the F-4 Phantom after Nav School, I never touched a sextant again. When we got some EO weapons that made sun angle important, we had to drag out the Air Almanac and remember how to figure that out all over again!
You made what seemed to be complex now quite simple, thank you!
It's not confusing at all. Like 0 confusion. What's next though?
Excellent and well done explanations, animations really make everything clear.Thanks!
Thank you Thank you Thank you - I just started to watch your videos on TH-cam and found them fascinating - I recently started to look at Celestial Navigation (just for the fun of it) and the sextant thing was a bit complicated until I saw these videos - Great Job !
Absolutely fascinating!
Thank you for your clear, concise teaching.
I've always wondered how these beautiful and complicated looking instruments worked.
It does seem a lot less complicated than it looks!!!
Thank you again!
I subscribed.😁
Isabelle in Victoria British Columbia
I love the animations in these videos.
Thank you so much for your explanation. Very nice.
I had no idea these devices were as complicated to use, as the are in terms of construction. Thanks for shedding light on these devices. :)
Just went to a museum today in Salvador, Brazil, and I was fascinated by one of those. Now I'm here looking it up 😆 completely in love with your video!!
Great work👏🏻
Very nice and helpful explantion. Keep up the good work God bless
Best explanation available
Perfect video!
I havent used a sextant since Junior Naval ROTC in high school (1971). Fotgot some of the details. You did a good presentation. 👍😀🇺🇸💯
Very good tutorial, you made it easier to understand than the others I've watched did. Now how do I compensate for the instruments height above the surface (i.e. deck height + my eye height)?
Great video
that was an amazing video. thank you
Awesome video 👏
A layman's question: Ok, the angle is 12 degrees and 26.7 minutes, but how is it projected to a map?
This tutorial talked about the sextant. The navigation with Sun or celestial bodies is another art, you must see other videos.
with a pencil.
Amazing info
very much helpful
excellent video! how do you manage to take an accurate site while the boat is rocking or do you wait until the water is calm
Thanks bro it helped me a lot
Oh sweet, this is exactly the video I was looking for.
Good explanation
Excellent explanation on how to use the sextant … but what do we then do with the sight measurement … how do we transfer that into a position on a chart ?
Yes,I was just now wondering that myself. It would be great if after you got your reading you would cut to a chart and show you transferring the reading to the chart. Then show another reading etc so we could see how you plot your course.
I think using the exact time of the sighting (gmt) and the angle, look it up in the tables to convert to latitude and longitude?
Interesting, and the angles it measures make sense, but this is only a tiny fraction of how to navigate by the stars.
It's also the reason I stick to rivers and smaller lakes. ;-)
Thank you for this video. Your animations provide a clear demonstrations of concepts without distractions or lighting problems a real life video would have.
What changes would be made if sighting by a star? I assume there is no upper- lower-limb importance. The fact the sextant can rotate to 120 degrees implies star sights. If it is dark can you really see the horizon? Is the match-up between two known stars rather than a star and the horizon ?
Is there an official name to the almanac that provides positions for every day each year? I would assume such a book would be reusable each year? Would leap years skew positions after Feb. 28th ?
Thank you hope I can give my viva best ..👍
Well Done & thk you
Good videos
Thanks..
Hey! Why did you delete your celestial sphere's video?
I really need that for my studies, please upload it again!
That one is due up again in the next few days..
Nice Animationen 👍
You should not read the angle once you have made the sighting, but note the time. Then read the angle.
Correct! The sextant holds the angle but time marches on...
Awesomeness
Besttt video
Thanks for this video 👍
Very clear, but how do I know what place I'm at with that degree? And how do I know where I should go? Also any star would work?
Thank you
Great
I got a GPS but I'm still watchin' this video
how did u say 12 25.2 (how to read mins and sec values sir) and off the arc why 1.5
Can we sit for a second and appreciate the gravity of the fact that someone thought of this?? First they conjectured that knowing the position of celestial bodies and the precise time ( like how did they even get an accurate time reading in greek antiquity???) could tell you exactly were you are on earth...then they meticulously compiled all of these accurate astronomical charts to make it possible and created the basis of the actual instrument itself... all with limited tools and resources due to their antiquity... just mind blowing that such smart people walked this planet....
What do you do with this angle? I need the rest...
When looking through the glass at the horizon with the lenses applied it creates a fibbonacci sequence
Ok so everything made so much sense to me until it reached the point where we are talking Almanacs (I believe that's what you said?) and upper/lower measurements of larger bodies. What I can't understand is why suddenly it's better to offset the body from the horizon? 3:45 are you measuring from the top AND the bottom of the sun in this example then using both measurements to somehow reach a perfect central measurement? Or am I wrong in thinking a central reading is the most accurate here. Thanks :)
Jes you are right, almanac gives you option to fix offset in case of lower or upper measuring of body. With stars it is easy as it is presented as small dot on horizon but when you put down moon or sun it is hard to objectively decide if it is correctly devided by half. Also lower or upper fix gives you option to measure in bad visibility when only one part of body is visible (clouds, etc.)
Ty
TY
As a landlubber, I always thought you move the arm but you actually move the instrument. Well, live and learn.
You can do that too, depends on the individual's preference. If the object is faint, like a star or planed, you move the instrument while tracking with the arm. But for the Sun it is easier to look at the horizon and just move the arm.
Without the electronics equipment and the channel markers, I would probably still get lost. I'm now going to get better at studying with the great job you've all done with the series of videos you've done. Much appreciated folks. How people from days of old managed to sail around the world, with all that is still trying to throw a wrench in the gears . What great works. Thank You so much.🧭 Wishing you fare winds and following seas🙏🧭👍
Thanks . How does it help you identify your position?
Not entirely sure myself, but I think that the angle between any celestial body and the horizon will be different at any time in the day, and position on the planet. Obviously more to learn here, I will have to subscribe.
And what about the precessionary movement of the earth in the seasons. In winter, the sun is less high in the northern hemisphere and more in the south. There's a correction for the day of the year. This also affects the pole star which wobbles a bit in degrees depending on the season. It would be nice if you could comment on this.
If you look at a nautical almanac you will see how all these various factors and corrections are accounted for.
Nice, but how does determining the angle of a celestial body (sun, star etc) which are in motion as is the earth allow you to determine your latitude/longitude ? I was watching this documentary on the Titanic and the relationship of other ships in the area reporting icebergs and referencing the lat/long of those. How are they able to calculate those fixes ? Also what did they do during periods of overcast skies ? Thanks !!
Funny to think that it must've been the bad/noob navigators who wore an eyepatch. Makes sense in a way.
Will there be a part 4?
4 what?
I still don't know how it's possible to take accurate measure in the rough sea condition.
How about a video on how to use the angle you just found?
I am embarrassed to ask. How is the horizon chosen chosen when using a Sextant on land? David Thompson one of the two earliest explorers of Western Canada created explored and created maps for the Hudson’s Bay Company in 1805. He made amazing accurate maps. The valleys and hills present a problem when selecting the horizon. How would he have done this with some reasonable accuracy.
by using an artificial horizon
An "artificial horizon" can be a bubble tube or a reflecting bowl of liquid. On the Lewis & Clark expedition they just made observations and recorded them so that someone else could do the calculations later when (and if!) they returned. The only differences are that the angle is doubled and there is no correction for height of sextant above the water level. A bit hard to see stars reflected in a bowl of water if there are other lights nearby.
I wish you had explained the "hours" figure you gave. I understand the degrees ° reference, but not the "hours" figures you mentioned.
how do i find index error sir thanks for a great vid more power No 1 fan here sir
Check the 2nd episode for errors and method of correcting them.
Could you do a theodolite video
Ive done thousands of km by foot bike and boat. Learning how to use proper nav tools is on my bucket list but im terrible with numbers.
What a good sleep. This I can see many times.
And HOW do you use this information to tell you your latitude?
You have to understand the principles and do some maths!
Ok I get the degree number but where do you get the minutes number from?
As far as I gathered from the drum at the bottom of the arm.
But what do the minutes mean??? Like decimals of an angle? Like 12.25 degrees??
Can you take a sighting inland at altitude?
I read you could reduce the celestial body on a flat piece of water , to create a horizon but how do you account for altitude e.g on the African escarpment?
Use a bubble sextant, where the horizon is replaced by the bubble (used in aeroplanes). Not sure if the altitude of the users eye makes a difference but in a 'plane you can get it off the altimeter. Sorry I can't give you more as I never used one, I only serviced them in the instrument bay. The bubble will also allow you to be sure the instrument is vertical as the bank (or roll) angle changes.
Yes you can using a bowl of water or some liquid which reflects the light from the Sun or Moon. Difficult to see a reflection from with stars and planets. The height above sea level is not important. The word "altitude" refers to the angle, not the height above sea level, which is confusing.
how nautical measurements ie cable fathom nautical mile fit into navigation
1 cable= 600 feet
10 cables 1 nautical mile
1 nautical mile = 1 minute 1/60 of a degree of the earth
"1 nautical mile = 1 minute 1/60 of a degree of the earth" - yes, but only to within 0.4% (worst case, which is for a great circle through the poles)…
@@TruthNerds But you measure your distance from the latitude scale on the side of the chart and not from a scale ruler, so that is where the slight difference you mention is adjusted for.
How to take vernier scale reading
I watched all three videos and still have not a clue how someone on a ship without GPS can find the ship's position using a sextant. How about explaining that. Thanks.
Oh yes simple just simply note the minutes at the degrees of the angle like in the video he said it was 12.5 degrees 25.2 minutes (with the correction) so he must of been in Tashkent Uzbekistan standing in the phone booth on the corner of Lenin Avenue and Bashalanbeh street. ..... but it also seems he was 5 inched of the ground.... maybe he was wearing high heels? Or maybe the phone booth was being used as unofficial a trash bin and he was standing on a pile of refuse... we don't know for that you would need an astrolabe.
One question. If you measure from the base of the sun to the horizon do you not need to then measure from the top to find the centre? If so, why not?
If you measure from the base of the Sun, commonly called the lower limb, you simply add the semi-diameter of the Sun. If you measure the upper limb you subtract the semi-diameter. The semi-diameter can be found for each day in the Nautical Almanac.
Taking two measurements like you suggested would mean the Sun would have gone up or down between the two sightings and you wouldn’t be measuring the same thing.
Some sextants (e.g. Davis Mark 25) have a "beam converger" which does what you suggest. The Moon is not always ful so you have to choose the top or the bottom depending on the lunar phase. For stars and planets the conventional sextant works just fine.
what do you mean when you say "minutes"
Minutes are a fraction of a degree. A minute is 1/60 of a degree
Fantastic. Heading to bed now 👍
I want to make a sextant, are plans available? I made metal parts for gemtop canopies down too 64ths.. Over years I cut millions of parts error free. So I think I can make a sextant.
My ship is constantly rocking STOP How to attain a reading QUESTIONMARK
ii'm just hoping if you continue to solve until the end hehe
Thank you. My dad left me his without instructions.
Very interesting
Now how can you use this angle to determine where you actually are?
Don’t worry I’ll confirm the answer against my mobile phone’s GPS 🤠
Assuming you are not in the Gulf of Aden where hostile forces have spoofed GPS at times. In a war, GPS could well be disabled deliberately or through enemy action, which is why the US and UK Navies 9among others) are teaching sextant navigation again.
Very interesting. I'm not trying to be silly here, but can someone explain how this knowledge can defend a flat -earth argument?
It can't.
@@throwawayavclubber7269 ok
This tool measures an angle, measuring an angle is easy no matter what shape the planet is. Celestial navigation on the other hand REQUIRES the earth to be a sphere. Celestial navigation works, therefore the earth is a sphere.
My question is: why did I watch all 3 of these knowing damn well I’ll never use one of these???
Honestly I think your video was great so it’s not your it’s me. I still don’t understand with clarity what this device is for
It was part of the navigational procedure to find your position on the oceans before the advent of GPS, which incidentally is operated by a few governments and could conceivably be switched off or degraded during an international conflict. It also provides a backup for a sailor if the GPS should become defective, apart from the entertainment it gives to anyone with an interest in astronomy.
👍👍🇧🇷🇧🇷
I learnt nothing from this tutorial about how to use this instrument in any useful way eg to determine where i am
I don't know why would I need this knowledge, but it's better to know it that not
I have a sextet with we can you Help me to setting know the actual cost currently it’s a London maid scooty 1753
i hate my school project
I love learning in my spare time?
Having taken a reading.... then what?
'... then what?'
Note the exact time the sight was taken.
Refer to the Nautical Almanac to determine the geographic position of the celestial body you sighted.
Do the sight reduction.
I've taken the liberty of creating a playlist for this series: th-cam.com/play/PLetA5Fi4kpULSexPc4Xul4Uq-8HoqifOd.html
You might want to present a question (a problem) first and then show how it can be solved (answered).
Example: You're lost at sea and have a sextant.
Assuming you have a chronometer and an almanac plus sight reduction tables or a calculator, then you try to get a position fix. The noonday Sun is a good start. However, it is really intended for navigation when you start from a known place and are going to some other location in a boat or an aircraft, so you will have some idea where you are, e.g. in the N. Atlantic, or the Indian Ocean or wherever.
Can you do a tutorial on how to sheer a sheep correctly?
Plz sell me
Er? You can't just take the angle. You MUST take the time as well. An angle without the corresponding time is USELESS for calculating your position.
Ideally yes of course. But for a few hundred years they only used latitude. There is a technique called "lunars" using both Sun and Moon (not always visible together) which doesn't need a chronometer. Very tricky to use but was used successfully by a famous sailor Joshua Slocum..
Yep earth is flat
Not according to celestial navigation
wow thats not sexy at all
So a sextant can only work only a flat infinite plane.
Celestial navigation only works on a globe. You need to know the location of the stars, you need a map of the earth and several key aspects depend on the earth being a sphere. Flat earthers have no map and do not know the location of the stars. There is also no flat earther who knows how to do celestial navigation.
too scared to defend your claim? atleast you have some sense.
Then you can go complete MCToon's sextant challenge by doing celestial navigation with your flat infinite plane Earth model. I'll give you a hint: there's a reason no one completed the simple challenge. All you have to do is do celestial navigation with a flat earth model. Why has no one done it? The reason is that Earth is a globe.
Rico wrong.
So tell us how this is possible. Its all based on Celestial Navigation.
Two people on opposite sides of the flat earth with their backs to each other look south and see the same stars.
They head further South meaning they are heading away from each other.
The same stars they see, get higher in the Sky meaning they are getting closer to the GP.
So how can two people heading away from each other can at the same time be getting closer to each other.. I can explain it on a Globe. Can you explain it on your Flat earth?