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...
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.
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.
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.
@@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.
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.
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....
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!
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!!
Thank you Thank you Thank you - I just started to watch your videos on RU-vid 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
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. ;-)
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.
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 ?
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)?
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.
This was very clear and explanatory, but now what? What does it mean, that the red object was 12.whatever degrees from the horizon? Does this tell us what latitude we're on? Thanks.
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.
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
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.
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🙏🧭👍
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
@@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.
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.
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.)
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 !!
You have to note the exact time at which the altitude of the celestial body was measured. Using that information you can determine the geographic position of the celestial body. A bit of spherical geometry allows you determine where you are relative to the celestial body's position.
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.
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.
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.
*This clown 🤡 debunked his own globe model!* 🤣🤣🤣 *He don't know basic trigonometry, if we measures any angles we must needs horizontal base line!* *Dumb@ss clown* 🤡
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..
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.
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.
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.
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.
'... 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.
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.
