Great! 😊 I've had to teach these concepts (and more!) to groups of 6th graders for many years! And, I've found out that, as adults, many went on to become blue water Sailors! The kids were always fascinated by my Grandfather's ancient brass sextant!
I was hoping you would also explain what you can use as references for the southern hemisphere, but this explanation and the why was very clearly explained. Thank you!
Of course it made sense. You're articulate as well as a good astronomy teacher. Please make a video on celestial coordinate system and elaborate all the technical details related to. A kind request.
The arc is on the sextant instrument itself. The ground never arcs, and neither does the sky. Just perspective on the plane. You cannot measure an elevation angle with a curved surface (globe).
@@tbrown3356 Wrong, we've been doing it for centuries. The "arc" is on the instrument as that's used to measure, just like graduations on a regular ruler, but a minute on the sextant translates to a nautical mile. Every degree is about 69 regular miles. If you try to plot it out on a flat sheet of paper, it won't work. It would be impossible for the Earth to be flat using the repeatable measurements of angles and distances we see everyday.
@@TheRealCreepinogie You're using the line of sight to the star and the horizontal plane (flat earth) to measure the elevation angles. The only arc again is on the sextant instrument. The ground can't be curving because you can't measure angles with curved lines. The sky also isn't dropping, but it's perspective making it appear that way. The celestial objects that you are closer to the geographical position of appear higher in measured elevation angles.
Hello from athens greece.one of the best videos.videos like this upgrade youtube.i dont know if you have video with astrolabe and how an astrolabe work(13 century astrolabe).but if you can make a video.thanks a lot.
The angle of the curvature (ie ... longitude ) between North pole and Equator is 90° . 1° is equal to 60' . 1' of arc is defined as a " Nautical Mile " , which consists 1852 Mts . So that the length between North Pole and Equator is 90 × 60 = 5400 Nauticals .
no actually the angles could be explained in a flat earth model but the angles would be very little in comparison which would negate the argument anyway lol.
Actually, John, there is no way to make this work on a flat Earth model/map. For one thing, the angle that Polaris is seen on the equator is zero. Not going to make a smaller degree than zero. And all of the other angles would not line up either.
Lol. Grab a globe and put it to the test. It doesn't work. (Use a protractor and see) However 90 degrees = 1725 nautical miles above true noth or 28.75 degrees × 60 which is half the distance to the equator of 57.5 degrees. That is a radius of 3450 nautical miles. So when Polaris is at 45 degrees latitude, it's half of 90 degrees and on the equator it's 0 degrees we know it's height:) If we lived on a globe and using your demonstration, Polaris would first of all start at an obtuse angle measuring from earth. 90 degrees + 23.5 degrees of earth's tilt = 113.25 degrees:) The sun is also the same height as polaris. Math does not lie:) Earth is flat friend
You can still use this same technique in the southern hemisphere, but you have to use the southern celestial pole (which has no bright star like Polaris), instead of Polaris, and of course the southern celestial pole would be measured with respect to the south (degrees above the southern horizon) instead of the north.
Hemispheres are a begging the question fallacy. You need a physical measurement of earth curve or r for hemispheres. And celestial poles are points on an IMAGINARY celestial sphere model. In reality you're just measuring elevation angles on a flat earth. Due to perspective all the stars appear to drop 1° every 69.05 miles away from the geographical position of the star. Welcome to flat earth!!!
@@tbrown3356 R is based upon the 96 miles per degree. In fact, it won't work at all on a flat plane. Then, to find longitude, one needs to know that each hour equates to the 15 degree per hour rotation of the Earth which is why accurate clocks were developed in the 18th century to compare local noon (when the sun was highest int he sky) to the home port noon. Each hour difference was 15 degree of longitude. It won't work on a flat earth.
@@TheRealCreepinogie The 69.05 miles per degree are measured elevation angles which require a horizontal plane. Get a protractor and you can see how the straight lines are measuring angles to the arc on the protractor. The ground cannot be curving if you are measuring elevation angles.
@@tbrown3356 You measure elevation angles from an instrument that has been leveled. It's done everyday by surveyors including myself. The horizontal plane is created by the leveled instrument. Ever seen one on a tripod? They do not lay the instrument on the ground.
To a traditional navigator things like GPS are very new and only by political chance available to civilians anyway. Its quite something to realise that young folk take the electronic systems as a given. It's like asking how Roman soldiers texted home. Quite shocking really. We learned the elements of CelNav in (UK) school about 14 yrs of age and today still use it in tandem with a modern ECDIS system. It might ?? have helped clarity here if the kind content creator (did a good job tho !) mentioned that altitude is measured from a Tangent to the earth's curved surface. That's the Apparent Horizon. Cel Nav does indeed seem to make use of a pre-Copernican perspective. Means nothing really ... the average person ought to be able to visualise celestial movement according to P-C and Proper motion (Heliocentric) at the same time .
Outstanding illustration. For some reason the FLAT EARTHERS don't hang out in these studies, do they?Kind of like asking a flat earther to pass a celestial navigation course, isn't it?
First step was measuring an elevation angle with a sextant. That requires a flat earth. You cannot measure an elevation angle with a curved surface (globe).
@@tbrown3356 Well, you clearly have no idea how to measure an angle and you persist in refusing to learn or understand, so it is quite pointless with someone like you who prefers to remain ignorant, opinionated and wrong!
it is more than 300 light years away, so far, that it appears stationary although it is in fact moving slightly, only apparent to astronomical observations over long periods of years. It is not moving around our Sun, but is moving with our Sun, and millions of other stars, around the centre of the Milky Way galaxy.
@@karhukivi Polaris is in fact off by around half a degree from the actual zenith of Earth's north pole, so it apears to be revolving in a very small circle. Something to keep in mind if you're dealing with very precise measurements.
@@johnsmith361 It is also caused by the Earth that is precessing, i.e. a little wobble like a spinning top does around its axis of rotation. It can vary up to almost two degrees but is usually less than a degree as you say. Accordingly, there are three corrections which can be made to any sextant observations of it to obtain a more precise latitude fix. These can be found in any celestial navigation almanac.
How is longitude determined only by celestial observation ? (Hint: If your answer requires use of a chronometer, I would point out that a chronometer is not a celestial object)
@@marcg1686 A sextant can not be used to determine longitude. Longitude determination requires a reference time and location, and local time. (we took celestial sights with a sextant to determine latitude and used a reference chronometer to determine longitude when I was in Naval Aviation in the 1950s)
@@walterbrown8694 A sextant always requires a 'reference time'. That will be GMT aka UT. The method you describe to determine your longitude is commonly used. If you are at a latitude close to the Equator you could sight stars with a low single digit declination. Alnilam, Menkar and Procyon spring to mind. Knowing the altitude and azimuth you could determine your longitude with reasonable accuracy. Also at higher latitudes plotting the zenith distance and azimuth on an actual globe will also allow you to determine your longitude with reasonable accuracy, accurate enough to allow you to calculate an intercept to another star. So you served in the Navy in the 1950s? That makes you about 90 years old.
It’s more difficult because there arent any bright stars above the southern pole. The process is a lot harder, so people dont tend to make short videos on it. Note that the noon-sun-angle will change by +/-23deg over the course of the year because of the tilt of the earth. So if you use the sun to determine latitude, you need to figure out the correction (which is called the solar declination).
You didn’t mention anything about adjusting adjusting for the dip angle and refraction. Your title is misleading and should state ‘in the Northern Hemisphere only’.
5 points reflecting polaris's position is Psedeuoscience. Quit asking me to do you a favor or prove myself. I commented on the stupidity. Sextants, compass ,knowledge of the stars ,speed and a flat horizon is how navigation was performed. Simpler question "does water always find its LEVEL? Cmon big boy.
simpler question? dont you mean since you don't know how celestial navigation works you need to change the topic? Why you need to change the topic? Why dont you want to learn?
It's your topic not me ne.Celestial navigation does NOT INCLUDE 5 Polaris. You still believe water bends ,but want to teach me something. Go learn about water and maybe your celestial navigation skills could be considered rational. Bendy water😂
Easily. We know that the 1st step is to measure an elevation angle which requires a horizontal plane (flat earth). The rest is just simple maths to create the celestial sphere model which is a stationary equatorial plane with a celestial sphere around it. That's what all globes and maps are created from, flat earth elevation angle measurements.
@@tbrown3356 Mapmakers use the geoid as a reference surface for the oblate spheroid model of the Earth - one model is called called the WGS84 and used by GPS systems. Flat paper maps and charts are projections of the spherical earth.
@@karhukivi WGS84 is a stationary flat earth with an observer at the center having a perspective sphere of equidistant celestial bodies rotating around the observer.
Uh, it wouldn't work on a flat earth as the angles would be different. Plot all the latitude angles from a flat surface and they won't all be parallel nor would they intersect at a common point. It only works on a sphere.
@@finoochebear9944Why would you tell me to learn how a sextant works when you just told everyone you dont understand celestial navigation. It's okay to be ignorant but you dont need to be a jerk about it.
So you need a flat earth to measure the elevation angle of stars. Then you can use the celestial sphere model with an equatorial plane (flat earth) as a model for globes and maps. But again earth is measured flat.
@@karhukivi There's no tangent to a geometric horizon (earth curve). You never have a straight line of sight to a geometric horizon (earth curve).With a sextant the observer is looking at the horizon. That's refracted (deviating from straight). So not a tangent to measure elevation angles with.
@@karhukivi "Distance to the Horizon The solid arc OH now represents the curved line of sight; H is the (refracted) apparent horizon" (Andrew Thomas Young).
@@tbrown3356 Of course there is a tangent to a curve, that is the definition of a tangent! There is a dip correction if your eye is not at the ground or water level, which it usually isn't. There is also a small correction for the refraction of the atmosphere for grazing angles especially, that is used for both celestial navigation and land-based topographic surveying. With a sextant you can look at a reflection in a bowl of mercury as well as the horizon. This might come as a shock to you, but hundreds of thousands of navigators have used celestial navigation over the last three centuries and it works - using the astronomical tables and spherical trigonometry which only works for a spherical Earth. Perfect proof that the Earth is not flat!.
@@tbrown3356 In the celestial navigations aka "almanac" there are corrections for refraction. You have a computer and the internet, so why not go away and study celestial navigation and when you actually understand it then come back to discuss the bits you don't understand.
Can you identify the 1/2 truths or not? Shows a right angle using a FLAT HORIZON. DEPICTS A GLOBE and starts lying. Pay close attention how the angles and " conclusive evidence than switches. Of course he totally omits conversion point in his discussion . As if you could see Polaris from everywhere. Then he shows decradating from Polaris lines that make no sense and is not what I observe. 5 angles of Polaris from 5 different sources?! Wtf? 5rays from 1 source is truth. How do right angles still work with a sextant when you're on a globe?😲 I know some how someway you convince yourself it is possible. Remember this technology is based on water always finds it's LEVEL. A tool researched ,devised,and invented for flat earth. It was reliable enough to successfully ship all that merchandise for centuries. Boy were they lucky that it still worked on a ball 😂🤣😂😉
@@robertlacaille7359 Hey Robert, you think earth is flat? Enough talking, you need to prove it. Solve this celestial navigation problem using only flat earth. Here are 2 real Sun sights. Find the observer's position. 1st Sun sight: February, 20 2010 17:26:26 UTC (GMT) Sextant: 40°18.2' Artificial horizon Sextant error: 0.0' Upper limb of the Sun 2nd Sun sight: February, 21 2010 00:16:02 UTC (GMT) Sextant: 24°04.4' Artificial horizon Sextant error: 0.0' Lower limb of the Sun No cheating now, you can't use globe science, only ''flat earth science''. Show all your calculations. GO!!!!!!
@@robertlacaille7359 There are lots of those videos. Even the balloons sent by flerfs show curvature. Find them yourself. Now prove flat earth YOURSELF like a big boy. Do a flat earth celestial navigation demonstration. Until then you have nothing. I’ll wait.
Lol. Grab a globe and put it to the test. It doesn't work. (Use a protractor and see) However 90 degrees = 1725 nautical miles above true noth or 28.75 degrees which is half the distance to the equator of 57.5 degrees. That is a radius of 3450 nautical miles. So when Polaris is at 45 degrees latitude, it's half of 90 degrees and on the equator it's 0 degrees we know it's height:) If we lived on a globe and using your demonstration, Polaris would first of all start at an obtuse angle measuring from earth. 90 degrees + 23.5 degrees of earth's tilt = 113.25 degrees:) The sun is also the same height as polaris. Math does not lie:) Earth is flat friend:)
John Perri, you can’t see Polaris from the Southern Hemisphere because the Earth is an oblate sphere. It has nothing to do with my eyes having a convex lens. Actually the lens of the eye is biconvex, which is why we are able to focus light coming into the eye onto the retina. Why do the stars rotate in a different direction?
@@uphollandlatic spin your finger around in a circle in front of someone. They will see the opposite roation as you do. So in Australia for example looking north the stars will rotate opposite as apposed to looking south.
Garbage. The distance from the geographic position of Polaris to the Equator is 10.000km and the circumference of the Equator is 40.075km. This only works on a globe.
