Sextant Tutorial: Errors and Corrections
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- เผยแพร่เมื่อ 21 พ.ค. 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 second in a series which will teach you how the sextant works and how you can use it.
This video covers Sextant Errors and Corrections. We will look at:
Index Error
Side Error
Perpendicularity Error
Instrument Error
Prismatic Error
Worm and Rack Error
Graduation Error
Centering Error
Collimation Error
In the next video, we will cover Taking Sights.
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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
I'm a Master Mariner and one of the last generation to use a sextant daily, good video but the best way to adjust for errors is to look at a dull star (bright get blurry), you get it spot on that way.
hey so are there any corrections for earth curvature when you are at sea? or are you traveling upon a level plane? it seems to me a level baseline is being utilized.
@@hillside6401 Sorry don't understand can you explain a bit more? If you mean navigation you treat the horizon as being flat at the point you bring the body (Star/Moon/Sun/Planet) onto it, which of course it is looking at it, is this what you mean?
Or do you mean when sailing the horizon is always flat but really the Earth is curved?
@@davidoldboy5425 ok sorry let me try again. When navigating at sea(with a sextant), are you making calculation corrections for the curvature of the earth? Dip correction is just height of eye right?
@@davidoldboy5425 are you sighting a geometrical horizon or a refracted 7/6r horizon? I’ve been told both by people who don’t use sextants. I’m just having a hard time figuring out how you could acquire an elevation angle from a curved adjacent seeing angles are two straight lines.
@@hillside6401 Correct dip correction is just height of eye
Excellent information on calibrating the sextant. I just want to add: don't be too eager to calibrate it. The process wears out the adjustment screws, with obvious consequences. It's best to write down the errors and use them in your calculations. Then maybe calibrate every few years.
Good point!
great content, thanks guys - especially with the sextant the animations are very useful!
In pre-historic ages under the old UK Board of Trade, there was an exam for deck officers called Second Mates orals in front of an examiner. To put the nervous candidate at ease, the first question would be to describe and correct the three principal errors of a very battered up old sextant. If you couldn’t answer that, you were shown the door.
Watching this video brought back memories of dusty waiting rooms, cheap suits and sweaty armpits!
Indeed, I too remember my 2nd Mates Seamanship Orals, all those years ago, under the old DoT (Dept. Of Trade) exam system
Absolutely fantastic series! Thanks a lot, so clear and concise. ❤🎉
This is very similar if not the same as measuring/linking-up a telescope with its finder scope. I had a pain setting up my newly bought scope. I didn't know these techniques, but I found away anyway.
TY for this explanation of the sextant this helped with understanding azimuth & navigation for Aviation use a little. The whole concept is new to me, but now I understand.
I have seen sextant, but didn't know how or why used. So Ty again.
Great video! Looking forward for more maritime topics
Thank you so much for the videos. Very clear. Now, I have to figure out how to use all the computers.....
Very useful video mate, I forgot everything on using a sextant, on the bridge with sextant in my hand now feel a lot better after watching this
You used a sextant? Are you some kind of sea navigator?
My dad was commander on a oiltanker. took my mother and me on board so i was 5 years old and visited many far away destinations.
At night i saw the universe and it dazled me.. then one night he brought me the sextant and tried to explain how it worked.
He talked about azimuth and words i hadn't even heard before..
Then he was pissed that i did not understand how this instrument works ;)
Now 60 years later i see your tutorials and i still can"t understand it..
I am more alpha then beta .
But i loved seeing this video's or anything about the Cosmos and i am a big fan of Carl Sagan but i think even he could not translate science to the common man ;)
thank you never the less for these tutorials and greetings from Holland.
I used to do science communication and this is a master class in making the tricky sound clear. BZ... as they say in Grey Funnel circles.
Haze Grey and underway!
Just knit-picking, at 5:10 you want your index arm set to 0, but the micrometer dial is still reading 25 minutes :)
Very helpful.. thanks a lot
That is so educational on many levels
Incredible information 👍👍👍
Nice, been looking forward to this one.
I have one
सर आपका कांटेक्ट नंबर नहीं है सो प्लीज एक बार कांटेक्ट करेंगे हमसे
thanks!!!!!!! very very helpful!
Not only used by mariners, but Meriwether Lewis used one during the Lewis and Clark expedition.
so well explained
Brilliant. I'd like to see how they evolved.
Thank You ! !
Very good tutorial on checking and correcting a sextant. Though, I would do mine at night, using a star rather than the horizon.
Awesome👍
when you set up to check side error do you set vernier scale to 0 as well as you did not say
It should be on 0 as you would have just eliminated index error for the first time
easy to understand , now i rmbr iy better
Thanks
Woot!
Why is the perpendicularity adjustable if it creates an error? Wouldn't it make more sense to keep it rigid and correct it at manufacturing?
I think while taking about Collimation Error you wanted to say parallel rather than perpendicular.
Can anyone please explain why the straight edge is an indication of perpendicularity of the index mirror? Like is there a geometric proof
why the arc is 120 degree?not more not less?
What is the difference between prismatic error and index error then!!??
I wonder how many 'sailors' will be entirely lost if the GPS system fails. 'Back in the Day' while making passage from Hawaii I remember my spouse asking why I was not taking noon sights and my reply was....all we can do is head north, when we get to the westerlies and turn toward Seattle, I'll get started. Of course then, it was blowing 40 and we were steering watch and watch as our vane gear gave up. -ex H-55 'Valkyrie'
👍👍🇧🇷🇧🇷
"Again? Sorry, I missed it... what's it called?"
"It's commonly known as a sextant, Eddy."
(Ed and Eddy burst out in laughter)
"SAY IT AGAIN, DOUBLE-D!"
Svensk?😁
Great tutorials!!!
Just one correctable error of note....your first slide in this tutorial should be #2 not #3!! (Sorry).
I've taken the liberty of creating a playlist for this series: th-cam.com/play/PLetA5Fi4kpULSexPc4Xul4Uq-8HoqifOd.html
Hi
Then there is the problem that a lot of folks just can't do the math.
I have one sextant 1917
have sextants really changed since the 1700's or not?
They have, most are now bubble sextants
The Germans even created a gyroscopic sextant for use in pitch black
Thank you! :)
@@rinislaboratories1315 - Bubble sextants are for aviation. Nautical sextants haven't changed very much, other than the addition of the micrometer drum, and the clamp.
@@robertgreen6027 - Rinis Labs isn't exactly correct. Bubble sextants are for aviation. Nautical sextants haven't changed very much, other than the addition of the micrometer drum, and the clamp.
Is this video 2, or video 3??
But what if the earth is flat😬
A sextant would work on a flat earth. It just measures an angle. The sight reduction wouldn't work though.
The order of these videos makes no sense. If you don't know how to take a reading at all, then you cant understand anything past video 1... So you are preaching to the choir.
can you explain how through your entire presentation all I saw was straight lines yet the Earth has a curve..... so how does this work on our planet
celestial navigation only works on a sphere. If the earth was flat how we do celestial navigation wouldnt work. Flat earth easily disproven.
Really small sections of really large curves appear flat to really small observers
Ever hear of a tangent?
Worthless. Explains in laborious detail the parts of a sextant but says nothing about how it's actually used and for what purpose. Does it locate latitude or longitude? How do it's measurements figure into determining naval or aircraft navigation? These are basic questions.
It does not give you a specific latitude or longitude. Instead it tells you how far away you are from the GP (geographic position) of the star you are observing. Typically on earth, each degree of angular deviation from your zenith to the star would equate to 69.1 miles of distance from the stars GP. i.e. 1 degree from zenith would place you 69.1 miles from the stars GP, 10 degrees would place you at 691 miles etc.
Therefore, this narrows you location down to a circumference around that GP. To get a more specific location you will need to take more readings of other stars.
The sextant just measures angles very precisely even on a moving boat. You need an accurate clock and an almanac of sun, moon, planets and star positions and a calculator (or reduction table) to calculate your position from the angles you measure with the sextant.