What does a Sextant Measure

[@freddan6fly]

Witsit has "flat earth celestial navigation all sorted out" but is scared witless from debating Celestial Navigation with McToon or FTFE. Thanks for another explanatory video.

[@BobtheScienceGuy]

he is terrified of trying that crap with me as well.

[@freddan6fly]

@@BobtheScienceGuy I've never used a sextant but I already grasped howto by reading a tedious 100+ page manual. I am not sure I can do it if it was a timed challenge tough. I have made it through Mc Toon's challenge but slowly, took several hours to find the position from 3 different stars. The thing with flat earth debunk is that you can always learn science from debunkers. Like blue marble and the cavendish.

[@BobtheScienceGuy]

Yep that was a great accomplishment

[@dogwalker666]

Actually there is no celestial navigation on flatopia as the sun would never set.

[@freddan6fly]

@@dogwalker666 Celestial navigation have only indirect with the sun to do but in principle, if the sun can't set, as on the flerftopia fantasy, there is not celestial navigation.

[@rodman2277]

Another great educational lesson...thanks Bob.

[@nymike907]

Cool stuff Bob. I appreciate the lesson. Reminds me of a teacher I had in high school who saw we were bored in a statistics class, so, he took us out to plot a hill with a transit (the school was not happy). Each team compiled the data and we combined it to look for accuracies and anomalies. Now fifty two years later it was an experience and teacher I will never forget.

[@RockinRobbins13]

Imagine a class of students, with cheap sextants in their hands, enduring the math they hate for the excitement of realizing they can find their location in the middle of the desert. When math becomes a vehicle to take them where they have a burning desire to go, they suddenly have a burning desire for math!

[@nymike907]

Exactly, and I thank Bob for continuing the experience of math being relevant for all kinds of activities

[@nickmartin1688]

What does a sextant measure? Salty flerf tears!

[@adamstrange7884]

You beat me to it!!!! 😅😅😅😅😅😅

[@Radwen_Rabbit]

Elevation angles from a flat baseline. Derp

[@Radwen_Rabbit]

@@nickmartin1688 elevation angles from a horizontal baseline.

[@freddan6fly]

@@Radwen_Rabbit Derp derp derp. Show your mathematics for how trilateration works, silly flerf.

[@estycki]

I think the thing that threw people off is they think they're on the _ground_ but you clearly pointed out your eye balls are the starting point, not the ground... and that makes a straight line to the horizon. I loved geometry in school - I'd love to see more videos on how to use a sextant, I might just get one for fun.

[@ElJefeS4]

Love a new Bob The Science Guy video!

[@Gdwmartin]

As a math challenged middle aged guy it's still clear as mud to me. I'd have to play with a sextant, and practice how to use it for a while for me to be familiar and confident in how hit works. However I still don't think the earth is flat.

[@RockinRobbins13]

Ah, one of those "learn by doing" guys. Don't worry about it. After you do it a few times you'll be as good as anybody.

[@Gdwmartin]

@@RockinRobbins13 I used to be much better at Geometry and Trig than Algebra in HS. That was a LONG time ago. I'm sure I could catch on fairly quick, but yeah i am a learn-by-doing kind of guy. It even works best for my Algebra to be that way.

[@RockinRobbins13]

@@Gdwmartin Hey, I was the same way. Then I took a course on the marriage of Algebra and Geometry, Analytical Geometry, and everything suddenly clicked as I realized the graphical way not only gave me the answers, but was self error checking while it told me why things worked. The final straw was when I taught myself Basic programming in the late 1980s and realized math is nothing but a language. That's when I learned Boolean math and became a bit fluent. But geometry was my gateway drug into algebra!

[@Gdwmartin]

@@RockinRobbins13 thanks for these bits info! I can wrap my head around Geometry and found Algebra difficult most of my life. Perhaps a course that ties them together is just the thing I need. Something to check out in any case. Thanks again

[@RockinRobbins13]

@@Gdwmartin I wish I could line screenshots of my work so you could understand them completely. Graphical solutions saved my life in math, as arithmetic mistakes are not obvious and have to be rooted out pretty blindly.

[@matty741]

This is awesome. How the hell did people learn this so long ago. Absolutely amazing what great minds can do.

[@BobtheScienceGuy]

it actually flows from a knowledge of basic geometry

[@matty741]

@@BobtheScienceGuy AHH fair one. Makes sense that I have no idea then. It's the kind of thing I look up when the kids have homework know it for a lesson and then forget again. I always love learning maths when I'm helping the kids though.

[@rayceeya8659]

Sextants measure angles. They're very good at it. You can even use one to estimate the curvature of the Earth using the amount of a mountain hidden by the horizon. I know, I've done it. I have three peaks that are roughly in a straight line. Mt. Tabor, Powell Butte, and Mt, Hood. I can take measurements from Tabor, across Powell and see ho much of Hood is hidden. Bam a good estimate for the size of the Earth.

[@BobtheScienceGuy]

I used mine to measure the distance to the sun a couple of weeks ago.

[@mikefochtman7164]

With a good tape measure to measure your distance away, you can even measure the height of a flag pole. hehehe... Yes, they have one readout and only one, the angle between two rays of light coming into the eye piece, nothing more.

[@deepfreezzeer]

Wow this is the best explanation ive heard of how to use one and what the purpose of each part of it is and what it do. It kind of reminds me about how GPS works, how your phone times how long a signal from the satellites takes to reach you and creates intersecting spheres in space of where you could be. That compared to the sextant showing calculated circles on the surface of the earth that intersect where you could be. Really well made video 😊

[@BobtheScienceGuy]

It isn't brain surgery. With 15 min of instruction and some basic understanding of math, I can teach to to find your location within 50 miles or so in about 10 min.

[@AT525LA]

Let's see if Oakley remembers not to mock you for saying that sextants measure "altitude" this time. While "analyzing" one of your other sextant videos, he paused it after you said "altitude" and did one of his maniacal laughs mocking you for saying that sextants measure "altitude." It took me about 25 comments going back and forth explaining to him that he has so little knowledge of sextants that he does not know the most basic of basic terminology associated with them. Obviously he though "altitude" could only mean how far away from the surface of the Earth the object is. I liken it to claiming to be one of the greatest hockey minds in the history of hockey, but then saying "icing" is not part of hockey because hockey does not involve cake decorating. It was classic Oakley and why we all love him so much!

[@BobtheScienceGuy]

yes he is amusing.

[@marsa7600]

A sextant measures angles, horizontal or vertical. The vertical angle measured between a celestial body and the horizon is called altitude. Altitude - The altitude of a celestial body is its angular distance above the horizon. Showing he has no idea about celestial navigation

[@AT525LA]

@@marsa7600 Yes - that was my point

[@friiq0]

I think some viewers might get confused and assume that point S is the physical location of the star, when in reality it is just the intersection of the vertical at the horizon and the line of sight to the star. Of course, the substellar point is not guaranteed to be right at the horizon every time. It might be helpful in a future video to translate the zenith angle down to the center of the earth. That might help show the location of the actual substellar point (which would end up considerably beyond the horizon in this case) and why the zenith angle gives you the angular distance from that point. Anyway, I don’t mean to nitpick your video because this helped me understand how a sextant works really well! I’m just a geometry teacher myself, and I’m constantly trying to anticipate possible questions and points of confusion my students might have. Keep fighting the good fight, Bob! 🫡

[@JSSTyger]

How come Nathan Oakley couldn't teach us this? He knows all about sextants (supposedly) :D

[@robertlafleur5179]

I gave Nathan Oakley a Celestial Navigation problem to solve using _’’flat earth science’’_ only. He gave me some excuses and didn’t even try. He knows it can’t be done using flat earth because he knows Earth is a globe. He’s a scammer.

[@freddan6fly]

Lol yeah, the only thing Nathan knows is to slap his daughter into crying.

[@stringtheorysucks]

Oakley has never touched a sextant, and he wouldn’t even know how to hold one

[@dogwalker666]

Because slappy dude Oakley could not find his bottom with both hands.

[@bosunbones.8815]

​@@dogwalker666even if he had a map and a flashlight.

[@RealityCheckThat]

I've always wondered how sextants worked. Thank you for explaining it.

[@thecasualengineer99]

@BobtheScienceGuy I have never used a sextant either, but i have gleaned a lot from this video today.

[@chrisclarke7274]

It measures the stupidity of flerfs 😂

[@mjjoe76]

We haven’t invented a device that can measure something so stunningly huge.

[@mikefochtman7164]

I think you slipped up a little @ 4:45. You said, "If my zenith angle is 60, then I subtract that from 90 to get 30 and multiply by 60 nm/degree...." No, if your *observed* angle was 60 (after dip and refraction corrections), you subtract that from 90 to get a zenith angle of 30. Once you have the zenith angle, you just multiply that by 60 nm/degree. You showed it correctly on paper, but when holding the globe in your hands you seemed to have used the term 'zenith angle' when you meant the observed angle gets subtracted from 90.

[@BobtheScienceGuy]

Excellent catch. Yes I misspoke and reversed it. You win the internet today and well done !

[@stauffap]

Great video! I didn't know that you can find latitude and longitude with just a sextant. It's fascinating how much you can figure out with a bit of geometry and some creative thinking.

[@BobtheScienceGuy]

Well technically a sextant and a watch if you don’t already have your longitude

[@stauffap]

@@BobtheScienceGuy Of course. I forgot to mention the watch. Thanks.

[@frankdebrouwer-leiden]

What flat earthers haven't found out is that there is no formula to calculate the distance from observer to GP of the star in a right triangle of which you only know the angles. You need to know at least the length of one side of that right triangle in order to calculate the length of the other sides. That's when they go wrong when they use the 60 NM/degree formula, if that formula were applicable, they they would have solved the problem of the length of a side of a right triangle when you only know the angles. They not only believe that there is a right triangle in celestial navigation (quod non), they also believe that you can calculate anything from that right triangle, that btw isn't used at all in celestial navigation. That's typical behavior of flat earthers: they hide one blunder with yet another blunder.

[@earthrise3672]

In the mid and late 80's, I used to have an old steel sextant, that came as part of the safety equipment in my 1958 28 foot Chris Craft with the double plank mahogany, and twin 6 cylinder inboard engines. Along with the life jackets and flare guns, there was a sextant, along with an old manual, and a star almanac from the late 1950's. I only used it twice just for fun, because I bought the outrageously priced ($3,000!!) Magellan GPS that just came out in 88 or 89?. I'll be damned if after reading the manual, and using the 30 year out of date star positions, drawing actual circles on actual paper maps. I was 4 miles off (give or take 1/4 mile) from where the GPS said I was, the second and final time using it. It is bugging me now seeing your sextant; I don't think that sextant had filters on it like yours, but I don't remember for sure. Unfortunately, despite my "high minded" success with the sextant that day. The true bone headed 29 year old came out. I was at a beach club on Lake Erie, and there were no piers. So boaters had to anchor out in the deeper water, and wade or swim in. That night, a storm was rolling in. Despite being warned by the more experienced boaters to make sure my anchors were solid, and to use as many as I had on board. I had 4 more, and had one at the front, and one at the back. That boat ended up beached, and looked like the SS Minnow without the damage. But that boat weighed between 20 and 22 tons! I paid a salvage company $1,300 to dredge the beach, and make a channel to the deeper water. It seemed like a great success, so I anchored the boat back out in the deeper water, and spent the rest of the day at the beach club. Just before sunset, I decided to make my way back. It would be an hour back to Buffalo, and another 20 to 30 minutes down the Niagara River to the Marina. I started the boat up, and began to make my way, feeling like I averted a disaster. I did notice a slight vibration to the boat, but thought very little of it. After about 10 miles or so, the boat began to feel a little sluggish. I open up the bilge cover, and the engine covers to find the boat filling up with water. Fortunately I was coming up to Sturgeon Point, and a Marina that was there. However, when trying to make the turn into the marina, the water in the boat shifted drastically to one side, and the boat began to drive in circles by itself, and for some reason, that I still don't understand today, the alarm in the boat went off, which included an aircraft grade strobe light on top of the boat, and after about 2, 360 degree circles, I stopped being stunned and thrown to one side, and cut the power to the engine, which stopped the circular motion, but I could now see a good 2 feet of water in the cabin, and by now, attracted The Erie County Sheriffs that had several boats at Sturgeon Point Marina, and followed me in at a crawl, and by the time I made it to the launch, the boat was fully sunk, water right up to the main deck. To make matters worse, after a whole day and night of blocking one of the launches, one of the marina members offered to put the boat on his trailer, after other members donated large pumps to pump out the water. I told him that boat weighs 20 plus tons. He insisted it didn't, and put the boat on his trailer, that promptly collapsed his trailer, JUST LIKE I SAID! Yet this guy had the nerve to try to sue me for his trailer! Fortunately, the small town court heard evidence from one of the Sheriffs, that heard me push back on putting that boat on his trailer, and I wo n that part. But the boat, though it looked intact, was totaled. The brand new Chrysler 218 flathead 6's that were just remanufactured before I bought the boat, the heat, and air conditioning, and all the wiring was waterlogged and corroded. Marine estimates were $20,000 to $25,000. I paid $20,000 for the boat, so it ended up being salvaged. What happened was; when the boat was beached, it must have been laying on one of the drive shafts. It never bent the prop at all, but there was a very slight bend in the shaft travelling out board from the inboard engines and the vibration broke loose the fixture that ran through the hull. This is my bittersweet experience with sextants, lol 🤣 But if I had it to do again, I would never have salvaged that boat, and rebuilt those engines myself. At the time marine experts convinced me that they were so entirely different than automotive engines, which is just not true. Big costly mistake. I don't regret not filing an insurance claim though. I had insurance. But I would never get another marine policy if I had. So there you have it! lol 🤣🤣

[@robertlafleur5179]

Wow! what an epic adventure! 4 miles off? Guess you were born with a sextant in your hands. Imagine if you had an up to date Nautical Almanac you would have pinpointed your position.

[@earthrise3672]

@@robertlafleur5179 Lol, perhaps? I really should get another one just because of all the stupidity surrounding them.

[@antondovydaitis2261]

Thank you. Even though I have a solid grounding in mathematics, and knew the basic theory, the details really helped me, especially the practical mechanics and corrections. Basically, everything between "you measure the angle of the star above the horizon," and "draw the circles and see where they intersect." The details are important.

[@BobtheScienceGuy]

Glad it helped!

[@theegg-viator4707]

Dude, Dr Bob, this is excellent, thank you for the brilliant overview! Truly interesting stuff, AND to have the ability to calculate one’s position to within 2nm is awesome. 👍🏻👍🏻👍🏻

[@RockinRobbins13]

Oh! Oh! Oh! (waves hand around frantically) *Sextants measure masthead heights* in a marina. Many mango seasons ago I lived on a boat in a marina on the Intercoastal waterway in New Smyrna Beach, Florida. We had sailboats there and boats traveling north and south along the intercoastal would stop by frequently. All these sailboats had to pass under bridges, especially the newfangled 75 foot clearance hi-rise bridges that were replacing drawbridges. Lots of mariners suddenly had the need to know exactly how far off the water their masthead was because......reasons, like it's always good when you don't bend up your mast or snag wiring from the bottom of bridges. So I would mark the place on the mast that was exactly horizontal from my eye height when standing on the dock. It was easy to directly measure how far that was off the water. Then I'd set the sextant to 45º and back off until the top of the mast lined up with the sine on the mast. At 45 degrees, the distance away from the mast equals the height above the mark. Measure that, add the first measurement that we directly measured and that's the height of the mast over the water. But that's not the end of the story. The intercoastal waterway is a tidal estuary. The bridge has a clearance of 75 feet above mean sea level. So the boat owner had to correct for tidal state if his masthead height were within three feet of 75 feet in Florida. The further north you go, the greater the tidal extent and the greater your variation in actual clearance with the tide conditions at the time of passage. But that was on them. They paid me my $20 and I wasted it in youthful exuberance.

[@raymondsalzwedel]

The great thing about all conspiracy ideas is that it pushes mathematicians, scientists, and engineers (in that order, deliberately) to confront how we communicate, and to what end. Furthermore, if the intent is to educate, then winning an argument against a proponent of a fringe idea is both trivial and fruitless. Rather, the fervour of such proponents gives an avenue, and an audience, for a reasoned, respectful, but absolutely rigorous and ruthless explanation of the natural reality in which we find ourselves; one that can be harnessed for both good or non-good; self eggandisdement and hubris have the explanatory power to do neither, and are hence impotent.

[@BobtheScienceGuy]

Yep great learning tool

[@microbeta]

A simple explanation of the most basic operation of a sextant. I love it. Excellent video Bob. That's the sextant I have too (Davis Mk 25).

[@krisdevalle]

Cannot _wait_ for the half-dozen salty response videos from Nathan and co.

[@tamfang]

A flaw in the drawing: the distance to the star is misleadingly small.

[@henrypile2385]

Great short video! Thanks for clearing this up.

[@BobtheScienceGuy]

Yes I love these KZbin experts that don’t have the first clue about c nav

[@chriscasperson5927]

Is that a Mark III? If it is, I like what they've done to the main frame. It used to be a solid sheet of plastic with a tiny nubbin to hold. The solid sheet would often warp, throwing your measurements off. The most basic function of a sextant is to find the angular separation between two objects. If you have an object of a known height, you can quickly calculate the distance, but after a certain point, it will start giving you distances greater than actual. Why? Because the surface of the Earth curves.

[@BobtheScienceGuy]

Mark 25

[@hillside21]

An Air Corps navigator in WWII didn't use a curved adjacent, with no visible horizon at night or above the clouds. They used a bubble sextant that relies on that darn gravity to find horizontal.

[@BobtheScienceGuy]

The link A 12 and I have one

[@theblackswan2373]

Nicely done.

[@nexpro6985]

It measures the vast emptiness between the ears of flerfs.

[@AudiOhm]

Bob, you explain things that are easy to follow, unfortunately for Flerfs they cannot follow a white line on the road .

[@BobtheScienceGuy]

it isn't for the flerfs. did you enjoy it?

[@0LoneTech]

I enjoy it. Apropos white lines in the road, may I recommend "Matt Gray is Trying: Line Marking"?

[@darz3]

Excellent Bob

[@johndoe1909]

oh i know, i know! - ih wait, i see myself out, oh whats this pointy hat i have on my head?

[@Bunny99s]

Well explained. Though I think it's not the best diagram when your tangent point is drawn as the GP of the star. Flerfs (who don't understand anything) will be more confused by this diagram as you "usually" don't have a direct line of sight to the GP of a star except you're essentially at the GP and the star is about 90° overhead ;) I know drawing a diagram that matches actual real world situations is usually not appropriate as you can't really show the dip as it's usually very small compared to the distances involved.

[@BobtheScienceGuy]

I did scale it that way to show the angles

[@chrisconnors7418]

That’s educational. Thank you!

[@simonjohn9525]

As you're interested in navigation and if you haven't already seen Phuket Word's video 'Flat Earth Celestial Navigation 2', made about 2 years ago, have a look at it. At minute 7:50 he explains that the distance on a flat earth from the 'ground point' of a celestial object is equal to its angular height. In the same video at minute 31:40 (Yep, it's a long video) he explains to his audience that the distance from the 'ground point' of a celestial object is 90º minus its angular height!

[@djcie1018]

Where is Mitchell from Australia? If I remember correctly he specializes in using the sextant.

[@BobtheScienceGuy]

lol

[@horisview]

Wow, you got them good. Jeran‘s cultists are in a fury. 😆

[@BobtheScienceGuy]

Yeah they are pissed. Even flatzoid’s echo chamber chat was evenly split on ‘who won’

[@horisview]

@@BobtheScienceGuy i tried to have a conversation with him in the comments. it isn't possible. he twists and turns every word and straw-mans everything constantly..

[@BobtheScienceGuy]

DK big time

[@TheKitsuneCavalier]

In this video Bob is talking about the sextant. In the previous video he had a total station sitting on his table. I suspect Dr Bob is up to something.

[@BobtheScienceGuy]

You suspect right

[@judybassett9390]

You explain that dip angle includes height, refraction, and curve of the earth; then at 2:58 you also talk about accounting for refraction. Isn't this accounting for refraction twice? I enjoyed the video.

[@NicoLeDahut]

In some almanac you can account for refraction to refine your dip angle correction. Closer to horizon so dip angle is more affected by refraction

[@RORY1230]

It's because the first one is accounting for refraction of the horizon and the other is accounting for the refraction of the object. It's only included to make the angles as precise as possible considering it's supposed to be used for navigation.

[@BobtheScienceGuy]

Good responses below. And no it isn’t double counting. One addresses the star and the other the horizon

[@Maxxmentum]

Nice video, thanks. I wondered how the flatly confused explained the nautical navigation of the past centuries. ;)

[@archivist17]

Good clear explanation, Bob. You do know, however, that a simple 'Nuh-uh' from a flat earther trumps all of this... 😂

[@simonjohn9525]

Not quite right. Dip is only the correction for height of eye and results in an Apparent Altitude. After that corrections have to be applied for refraction for light passing through the earth's atmosphere and the one you forgot about, parallax. This is a very small correction but it corrects Apparent Altitude, measured at the surface, to an angle at the centre of the earth. It's from that angle that the True Zenith Distance can be calculated as you described. In the case of the sun and the moon there's an addition correction as the outer edge of each is measured to the horizon so their Semi Diameter has to be corrected for. Otherwise a good explanation.

[@adamstrange7884]

It measures a flerfs IQ, in billionths of a whole number!

[@OnASeasideMission]

A shedload of things I didn't know. Serves me right for not joining the Royal Navy. Thanks Bob.

[@gowdsake7103]

Was in the RN for 9 years never even saw 1😁😁

[@OnASeasideMission]

@@gowdsake7103 Good on you.

[@sthurston2]

Dr Bob, you made the classic mistake. You wanted to show the Earth and the star in an orthographic view. You showed a star that was only about 5000 miles away from the surface. The whole point of measuring the angle between zenith and the star depends on all sight lines from the Earth to the star being practically parallel, and that diagram says that isn't the case.

[@BobtheScienceGuy]

I is a diagram to highlight the angles

[@sthurston2]

@@BobtheScienceGuy I know but such diagrams lead to the misunderstanding that right triangles are involved.

[@BobtheScienceGuy]

good point.

[@knallertk8062]

Is the recfraction angle always "positive". Or can i go both ways? Thank you for this video. I always wanted to try using a sextant.

[@BobtheScienceGuy]

The almanac has the data to calculate actual refraction based on conditions at the time of reading (temp etc) but I’ve only used standard refraction

[@thomaskirkpatrick4031]

A sextant is the old fashioned method? Seems pretty good.

[@keitharika8906]

Have you had a chance to do astrolabe yet?

[@BobtheScienceGuy]

Yes I do have videos on my channel in their own playlist

[@keitharika8906]

@@BobtheScienceGuy Darn, didn't see them. Will look in the playlists.

[@chipbowers247]

​@@keitharika8906look for "equation of time"

[@dominiquefortin5345]

I'm unsure why you would have to take the angle of the star to the horizon when taking the angle of the star to my normal would already give me the distance to the gp of the star ? Is it because a boat is always moving and it's too difficult to obtain the angle to your normal ?

[@BobtheScienceGuy]

No you find the distance using the zenith angle

[@dominiquefortin5345]

@@BobtheScienceGuy Normal vector, zenith, practically the same thing for what I'm trying to say. I know the normal is perpendicular to the surface and the surface might not be leveled , but I meant the line that starts at the center of the earth passing through the observer. Why bother taking the angle between the star and the horizon. Then calculate the zenith angle of the star not forgetting to take into account the height of the observer the refraction which is error prone. When simply measuring the zenith angle directly gets you the distance to the gp.

[@BobtheScienceGuy]

that is how a bubble sextant works. In my experience with both nautical and bubble sextants, the nautical sextant is more accurate. This is due to the mechanics of how the bubble sextant works.

[@MartinJames389]

It seems a sextant can also be used to measure two other things - conspiridiocy and wilful ignorance. You don't actually need a sextant to do it, either, just a reference to one. Amazing! OK, "measure" is not really accurate. It indicates the presence of conspiridiocy or wilful ignorance. Wilful ignorance is measured on the Oakley scale. It is a metric scale, of course. 1,000 grifts = 1 Oakley (formerly known as the kilogrift). Conspiridiocy presents a different problem. It used to be measured on a local or domestic scale, based on the pub, 1 per pub being the general mean. However, the internet has thrown all that into confusion. It supplies no beer but an unquantifiable profusion of conspiridiocy. The proposed unit for its measurement is the Musk, of course, but a workable scale has yet to be devised.

[@konzekuenze]

The amazing tool that allowed my country to rule the World for several Centuries...

[@sissyfus6181]

Yeah, but don't forget John Harrison!

[@antongromek4180]

Oh, and I thought it is for measuring the length of something... (well, the first three letters are somehow misleading;)

[@BobtheScienceGuy]

Grow up lol

[@WitchidWitchid]

I doubt most flerfs could understand how it works. All those measurements and angles. Flerfs havent yet managed to figure out how many degrees are in a triangle.

[@freddan6fly]

They all have dyscalculia, because that is one necessary precondition to be brainwashed into the flerf cult.

[@rickkwitkoski1976]

That clears up NOTHING for the denial and flat earth camp. However, thanks for the quick explainer. Please do a vid showing you outside at night determining your location using your sextant if you haven't already done so.

[@BobtheScienceGuy]

Not for them

[@BobtheScienceGuy]

Well unfortunately it is dark and tough to video. Plus I generally use a bubble sextant at night

[@EmersumBiggins]

Bob has located his house for us in the daytime using a false horizon. Pretty sure he has a video on his channel.

[@84com83]

How do you se stars in daylight (except the sun)?

[@BobtheScienceGuy]

Well the sun is used. Also the bright navigational stars are visible at twilight in the morning and evening. That is when you do your sights. In darkness you use a bubble sextant

[@acesw6124]

Flatzoid and Witsit and many other flat earthers reject measurements and numbers and seem to think that words describe everything perfectly without failing.....

[@chassetterfield9559]

You were doing so well, Bob, until you started drawing circles around points on the Earth. My heart sank as soon as I saw you pull out a globe. It's a theoretically possible method, provided you have a computer, or a huge physical globe to plot on. But, that is NOT how astro-nav has been carried out for the last few centuries. How do I know? Apart from being a retired chemist & physicist from the pharma, aerospace [ space ] industries & academia, I trained in navigation, including astro in the 1970s. I HAVE been a professional navigator & sailing ship Captain. At no point have I ever reached for a pair of compasses to calculate a celestial position line. I'm currently writing an essay on the history & development of celestial navigation over the past 500 years. It looks at the development of techniques & equipment over that time. I also delve into old [18th /19th century] texts to look at how navigators were taught to do their trade. I was going to send you a copy of the finished piece anyway, but just might send you a copy of the current part finished draft now. I'm currently working on the section to 'reverse engineer' the tabular log methods in use, to find the underlying equations being solved. I already KNOW that they are spherical triangle formulae. YES, there IS a triangle, & it's spherical, NOT Flatzoid's SOHCAHTOA, and it is vitally important to the process. I very much admire you, & MCToon, & it grinds my gears when I see you peddling this tosh [ well, it is to me ]. How do you find the Davis sextant? I've got 5 or 6, depending upon whether you include the bubble sextant, but no plastic ones. The last plastic sextant I handled was an Ebbco, back in 1980.

[@RockinRobbins13]

Your nomenclature reveals your unfamiliarity with the method. I also have used a sextant. I also have navigated across bodies of water where land was not visible in any direction. I HAVE used circles of equal altitude (there's no such thing as a _"celestial position line"_ ) to graphically (not computationally, aside from correcting for refraction and dip angles) plot my position. One thing Bob left out purposely. Another reason you use three stars is to evaluate your error envelope. There is always a little error in measuring the angles, especially onboard a small boat or ship. When you use the three star method, the circles don't intersect in a point. They intersect in a little triangle whose size and proportions tell you what your error envelope is. If that triangle is a very small equilateral triangle, that may be the most accurate you're able to get. So you know you are within the size of the triangle from where you intend to be. Let's suppose the triangle is not equilateral and is a long skinny triangle. This tells you that the error in one angle measurement is greater than the other two. It would be a good idea to retake the observation on the star causing the problem to get a more accurate fix. You can understand that graphical means (we use charts of proper projection, not globes to do this) beats computational means all hollow! Not only do you get your position, you get an evaluation of how accurate your measurements were and the opportunity to correct the errors. Unfortunately, chasseterfield, you aren't familiar with the process.

[@BobtheScienceGuy]

Actually I did it to illustrate the concept of circles of equal altitude. Of course it isn’t done with a globe (although I have done it with google earth) the Davis mark 25 is s great sextant I I like it

[@RockinRobbins13]

@@BobtheScienceGuy To be fair, if you're drawing only a small part of the circle of equal altitude on a map of small scale, the arc that crosses your chart could functionally be represented as a line without much error at all. That might be what chassetterfield is referring to. Its sort of analogous to simply treating the ground as flat when building a house. The curvature is so slight it's just an annoyance to account for and doesn't affect any of your measurements anyway.

[@BobtheScienceGuy]

it is, and that is how it is actually done on plotting sheets.

[@EmersumBiggins]

We have the same watch, Bob 🙂👍

[@ollyk22]

Day use?

[@BobtheScienceGuy]

Noon sights use the sun

[@ollyk22]

@@BobtheScienceGuy Would be cool if you could do a vid on them too...?

[@matthewalker]

Have any sextants used a spirit bubble to get horizontal, or would that be too imprecise?

[@BobtheScienceGuy]

Yes but most folks just ‘swing it’s to find the bottom of the arc (vertical)

[@NicoLeDahut]

They will come after you, because your zenith angle is not equal to the angle to GP, on your diagram.

[@soulcrewblue8629]

Vampires and crucifax's don't mix well, flerfs and sextants.......

[@Lassisvulgaris]

Make that flerfers and science.....

[@entangledmindcells9359]

Any FE want to claim CN provides accurate results on a flat earth?

[@robertlafleur5179]

They might claim it but they never demonstrate it. I gave a CN problem to Nathan Oakley, Brian's Logic, Austin Witsit and asked them to solve it using _''flat earth science''_ only. Up to now they haven't done it. I wonder why, should be real easy.

[@entangledmindcells9359]

@@robertlafleur5179 I was hoping to get an FE to bite.. I take a different approach to this whole CN argument.. It goes like this. There are two stars in the Southern Sky are that are around the 70 degree South latitude that are part of the 57 stars indexed for Celestial Navigation. Miaplacidus at S 70degrees Atria at S 69degrees. What is special is that they are visible all night long for anyone 30° South or further South. I can place two people at say 30degree South at two locations 180degree longitude apart meaning on a flat earth the North Pole is between them & their respective "South"s are exactly opposite of each other meaning if they look to "their" South, they are looking exactly in opposite directions from each other. And the implication is, during their winter months, there is more that 12 hours of night meaning there is a time when it night for both & they can look to their South and see those very stars at the exact same moment. If they both head further South from their positions, they are moving away from each other. But those stars are getting higher in the sky meaning they are getting closer to the GP of the stars. Nothing like moving away at the same time moving closer.

[@horisview]

Flatzoid is already poisoning the well in Jerans live comments before the debate even started.. that’s typical flerf.. 🙄

[@fernandoaldekoa2436]

👍👍👍

[@xdragon2k]

If you have an accurate compass, can't you get your position with just one Zenith angle of one star? I mean you know which direction you're pointing your sextant toward.

[@BobtheScienceGuy]

Good question. You can get in the right postal code'ish, but no it isn't precise enough to get a position fix.

[@xdragon2k]

​@@BobtheScienceGuy I know the caveat is that you need an "accurate" compass. But what is the inaccuracy that can happen if we know it's 100% accurate compass reading? We have the circumference of the circle and we know the angle from the center of the circle. We can definitely hit the circumference with that line to a point, right?

[@BobtheScienceGuy]

Why are you talking about the circumference? Do you mean circle of equal altitude? Also you know the bearing if a great circle changes from the initial heading, right? That is why we use trilateration rather than triangulation

[@0LoneTech]

​​@@xdragon2k You describe having the altitude-azimuth coordinates of a star. Along with the star's position (almanac) and time (chronometer), this should suffice. Polar sighting is probably far more accurate than most compasses though; the magnetic field is more irregular than the gravitational field, and both vary over time as well. May I recommend the Stand-up Maths video "Once a Millenium Alignment of all Three Norths", also labelled "Matt Parker's North by North-North"?

[@xdragon2k]

​@@BobtheScienceGuy Yes, at the moment I'm thinking in 2D. I wanted an expert's opinion on why we're not using the heading of the sextant to get the location. I don't know the significant of heading is a sphere coordinate.

[@haraldlonn898]

Thanks.

[@youtubeuser6067]

Where can I order your nice sextant there?

[@BobtheScienceGuy]

It is a Davis mark 25. You can get them on line

[@lenny-q9s]

why would somebody who knows for a fact earth is a sphere spend so much time and effort to debunk non believers of the sphere earth? it makes no sense, I mean think about this , who has time to waist on convincing somebody about something if that person knows for a fact that it is true?? nobody would do this, unless like Bob the science guy is deep down unconvinced of earth being a sphere, bob knows he cannot guarantee earth is a sphere and this is his way of coping with it by bashing flat earthers

[@abdobelbida7170]

Why would flat earthers spend 15+ years lying about their desire to go to Antarctica if they will actually decline everytime they're offered? Doesn't make any sense, unless all flat earthers are liars always.

[@westsidegirlreacts]

How can a sextant measure an angle with a curved base? Huh?

[@JSSTyger]

A line of sight intersects the curve at the horizon and another line of sight is to the celestial object. Both lines of sight are lines so there is no "angle with a curved base".

[@westsidegirlreacts]

@@JSSTyger I’m debating whether to keep trolling. So a sextant isn’t curved?

[@BobtheScienceGuy]

Watch the video before commenting. Answer is right there

[@AlexZander688]

...Didn't you watch the video? @4:13 Bob explains it quite clearly. #1. Don't listen to flerfs who have ZERO real world experience using a Sextant. As of yet, none of the KZbin flerf leaders have ever done a successful fix using a 'real' Sextant, on a real boat, on the real ocean, etc.(you will end up lost at sea and dead.) #2. Watch, listen and learn from real world experts that have successfully performed Celestial Navigation. or #3. Buy yourself a nice Sextant. Enroll at a Maritime Institute and complete training from real world experts.( you will NOT end up lost at sea and you will still be alive.)

[@freddan6fly]

Are you a flerf? Why didn't you watch the video?