In the 1600's they did not use this method. A clock that would keep accurate time at sea was not invented yet. They used the lunar distance method, using almanacs with celestial data.
@@jackjones9460 It's called the "lunar distance" method and requires a sextant observation of the angle between the sun and the moon - which is not a usual situation and not easy to do either. Google on "the nautical almanac" for some online resources. Some of them will give the lunar distance tables. Otherwise, if an accurate clock set to GMT is available for an ocean voyage, the same almanacs give the meridian crossing times which when compared to the local noon time (corrected for the "equation of time") give local longitude.
but how do you know it's 6pm on the ship? it seems like you'd just have to wait until noon everyday, and that would be the only time when you could accurately determine your own time, and thus the only time to compare your time with what your clock tracking Greenwich time. we're skipping the most important step, here.
You have to determine solar noon, which is usually not 12:00. Solar noon is different every day. You compare your solar noon based on the known solar noon time at Greenwich.
this video does not show how to find longitude using celestial observations - as per the title... it is about longitude using an on board clock sit to GMT
Also the Time zones are not hard and fast as shown in this video, for example China is a big country yet uses single timezone and US on the other hand uses 4 time zones.
Ok how do you know what local time is??? For example. I leave Spain at 3p local time, and sail on a westerly heading for 3 hours, with a 10 knot headwind, my watch now says 6p (left at 3p, sailed for 3 hours) what longitude am I at now???? Your assumption is that I KNOW what local time is (which I would not know at all) meaning that if I only move 10 feet in 3 hours, my time has changed but my position has only moved 10 feet. The question still has not been answered: how do you calculate local time if you dont know where you are?? With a ship rolling and pitching It would be hard to use sun shadows. Help me here....
roy Yung so you fix at noon. You know for sure that its noon when the sun is at its highest point. This also makes declination easy for lattitude fixes with a sun shot. Because declination will be 90 degrees
Suppose you have a watch set for GMT. You shoot lattitude at noon. It says 645 p.m. gmt when you do that. You would be 6 hours and 45 minutes behind (west) of greewich. Each hour is 15 degrees. So converting 45 into decimal hours gives you .75. So 6.75 x 15 = 101 degrees 15 minutes longitdue
rou Yung: Knowing local time is not a requirement. A navigator who knew Greenwich time (either from a chronometer or from Lunar observation) measured the angular height of a body. He then corrected that height for the effects of instrument error, atmospheric refraction, parallax, semidiameter, etc. Then, using that height, his best idea of his longitude, and the Almanac's predicted coordinates of the body he computed (or found in a table) the longitudinal difference between the body and his position. That gave him the longitude at his estimated latitude. Later navigators did this procedure twice, each time using a different assumed nearby latitude. That produced two lat/lon fixes which could be marked on a chart; a line through them was the line the navigator was on (or near). If done again using a body seen in a different direction, the navigator could cross the lines of position on the chart and have an approximation of his position.
i imagine it's reasonably easy to pinpoint the time within a few hours within at least the tropics, but if you get further north or south, it actually is fairly difficult to guestimate the time from the sun alone.
the time which the vessel presents is the zone time , its the same time of any thing which is placed or sailed in the same zone however the difference between them in position, that mean if there are two ships, one of them on long 15* degree and the other on 20* degree, both of them will have the same time, regardless that they are not on the same longitude !! because both of them sailing in the same zone (zone number 2 in this example) ! so, you can only calculate the zone number by using this method ( using the D.LONG) . if your vessel’s time & Greenwich time are given .. you can calculate the zone which the ship sailing on, without determine it’s longitude, if you check your video, you can only calculate 15* 30* 45* 90* 105* degrees ! difference 15* degree ( ranges of zones ), you cant calculate if the ship on long 17 for example! this method will be correct only in one case, if the ship sailing on its zone’s middle .. because the time of the zone = the local mean time of the middle of this zone, BUT you cant depend on this idea because you already don’t know where you are :)
Celestial means using the sky, or bodies in the sky, such as the sun (which is a star), other stars, or the moon. In this case the presenter is using the sun. Latitude may be determined by measuring the angle of Polaris ( the North Star) above the horizon.
So technically if you knew your lattitude and you took a noon reading at your location, then began to travel you would still be able to know your longitude without using GMT, would that be correct?
Man I’ve been looking into these question to no avail. But you’re absolutely right. You have to calculate true noon while traveling on a ship which requires a device called a sextant. I’m still working on figuring it all out. Haha
One may wonder in that if Polaris could be used in determining latitude, why can't a particular star, any bright star as the reference point since stars also rise in the east and move westward. That is, set the clock in Greenwich when that particular star is on the meridian much like what's done with the sun. The only difference is the sun is done in daylight while it's nightime with the star. Sidereal noon, for instance.
And if the clocks match perfectly, you could be in port at London, or anywhere within that time zone which is a 7 1/2° radius in either direction of port. So margin of error is never less than 7 1/2° longitude.
Timezones are purely political hocum. Local solar time is the true local time used in the video (really local solar position, but time is a close approximation.).
At noon in your location the sun is at its highest point. Reset your local watch to 12:00 then compare to your other watch set to GMT. You’re OOL if your clock set to GMT is broken, though.
Sailors in the 1600's wouldn't have been able to use this method for determining longitude as they didn't have timepieces that were accurate enough to keep track of GMT. Even in the very early 1700's it wasn't possible. It was only after John Harrison presented his first clock to compete for the longitude prize in the 1730's did it become a real possibility. Even then many years were to pass before he finally presented his 4th attempt which was the watch that was to finally win him the prize.
There were other methods for determining longitude before this, such as using the transit of the moon or the relative position of the moons of Jupiter. I gather the difficulty with these methods come down to taking accurate measurements; these methods are what I was looking for when I ran across this video.
HOW DO YOU CALCULATE LONGITUDE WITHIN A TIME ZONE- ARE YOU ON THE EASTERN OR WESTERN SIDE OF IT OR ARE YOU IN THE MIDDLE?? IS THIS NECESSARY OR EVEN POSSIBLE??
There is a problem with this method. If the ship is anchored and is not moving from its current position, the clock continues to move forward. Therefore the clock's difference to GMT is irrelevant to current position of ship.
You have the concept ok but totally screwed up on the details. First off AM/PM are some antique ameture BS, navigation has always used proper 24 hour clock times. Second is the very common mistake of mis-using GMT. Solar noon on the prime meridian is 0000GMT, 1200 GCT or 1200 UTC. (and GMT stopped being a thing 100 years ago, and the GMT date changes 12 hours before the normal civil date. UTC replaced GCT 53 years ago.)
To acquire a more accurate longitude you will need to include minutes and seconds of time not just the time zone hour, or you may be many 100's of miles off.
@@Somethingisntright64 I am talking about how you'd find the time, although there's more to it than I say, like true solar noon versus observed solar noon.
If you don't have a clock set to GMT is is almost impossible. However there is a method which is quite a challenge using the angle between the Sun and Moon - providing both can be seen at the same time, not always possible. A number of special charts or tables would have to be available onboard. This method is known as "lunars" and was used by a famous sailor called Joshua Slocum.
Although your previous video of calculation of latitude was correct but this one is not(fully). GMT was established in 1884 by international meridian conference. If it were said by you," So, imagine that you are a sailor in the 1800s and....." it would have been correct but you said 1600s or 1700s. Other than that, the video is 100% CORRECT(for the people who said it was wrong). Keep making these type of videos... They are very usefull... -From INDIA.
Im a complete newbie to this but, how can using a clock give us longitude. There is no accounting for bearing, currents and winds. This doesn't make any sense at all.
Oops, what if you’re south of the equator. You basically start off with a little boat going into the Southern Hemisphere, then proceed to say you can use Polaris to determine your position. Do you see a problem here?
@@jackjones9460 there are a number of stars that can be used depending on your position. You need the nautical almanac and you need more than one celestial body.
@@jackjones9460 there are plenty of other celestial objects to chose from. Learn about celestial navigation, the celestial sphere, the nautical almanac.
I hope im not stupid :) If i start at GMT and take a a boat or on a plane and fly for 10 hours and look on my clock. If someone cant tell me what timezone im in im lost? AND if they say.. oh its +4 hours, then i already know what timezone im in? HOW can i determine longitude using celestial observations? like polaris for longitude? This video told me "Your in New York, change your Clock 10 hours to our time... do u know where you are now??" nothing about noon mentioned here?
This makes no sense, if I have a clock on the ship set to local time, then I already know where I am. send the ship out to sea where they dont know there local time and this demo fails
I’ll keep it simple for the simple minded on here. Time was determined by an hourglass. This was turned by the officer of the watch every hour. That is how one determined time. Simple…..just like some of you lot.
thanks for the video...very clear yet simple...can you please help me in understanding RA and Dec and second how to calculate degree of few other stars
Doesn't matter for this type of navigation, just as it doesn't matter for the clock in your living room when you want to watch your favourite TV programme!
Seth very good video but you might consider editing the video to also an include and example of when the ship is in the west and local time is in the PM of a certain day and the GMT is in the AM of the next day.
Wrong, chronometers were not invented until 18th century, so this method was not used in 15th ,16th century as claimed in the video. Also the video title is wrong as you are not using only celestial measures but a chronometer as well.
agree, this is stupid and trivial. Besides an accurate on board clock/watch for GMT, the other important piece to know on ship is to determine local time. This video seems to trivialize this part, which is not.
In the 1600's they did not use this method. A clock that would keep accurate time at sea was not invented yet. They used the lunar distance method, using almanacs with celestial data.
Peter Linn I just completed an online class with Frank Reed Navigation, and he discusses this in detail over several days.
Hourglass
Almanacs of celestial data to find longitude? Very interesting. I’d like to know how.
@@jackjones9460 It's called the "lunar distance" method and requires a sextant observation of the angle between the sun and the moon - which is not a usual situation and not easy to do either. Google on "the nautical almanac" for some online resources. Some of them will give the lunar distance tables. Otherwise, if an accurate clock set to GMT is available for an ocean voyage, the same almanacs give the meridian crossing times which when compared to the local noon time (corrected for the "equation of time") give local longitude.
but how do you know it's 6pm on the ship? it seems like you'd just have to wait until noon everyday, and that would be the only time when you could accurately determine your own time, and thus the only time to compare your time with what your clock tracking Greenwich time. we're skipping the most important step, here.
You have to determine solar noon, which is usually not 12:00. Solar noon is different every day. You compare your solar noon based on the known solar noon time at Greenwich.
this video does not show how to find longitude using celestial observations - as per the title... it is about longitude using an on board clock sit to GMT
It's actually. Sundial
Also the Time zones are not hard and fast as shown in this video, for example China is a big country yet uses single timezone and US on the other hand uses 4 time zones.
Ok how do you know what local time is??? For example. I leave Spain at 3p local time, and sail on a westerly heading for 3 hours, with a 10 knot headwind, my watch now says 6p (left at 3p, sailed for 3 hours) what longitude am I at now????
Your assumption is that I KNOW what local time is (which I would not know at all) meaning that if I only move 10 feet in 3 hours, my time has changed but my position has only moved 10 feet.
The question still has not been answered: how do you calculate local time if you dont know where you are??
With a ship rolling and pitching It would be hard to use sun shadows.
Help me here....
None of it adds up, because the earth is FLAT.
roy Yung so you fix at noon. You know for sure that its noon when the sun is at its highest point. This also makes declination easy for lattitude fixes with a sun shot. Because declination will be 90 degrees
Suppose you have a watch set for GMT. You shoot lattitude at noon. It says 645 p.m. gmt when you do that. You would be 6 hours and 45 minutes behind (west) of greewich. Each hour is 15 degrees. So converting 45 into decimal hours gives you .75. So 6.75 x 15 = 101 degrees 15 minutes longitdue
No, it’s a glove
rou Yung: Knowing local time is not a requirement.
A navigator who knew Greenwich time (either from a chronometer or from Lunar observation) measured the angular height of a body. He then corrected that height for the effects of instrument error, atmospheric refraction, parallax, semidiameter, etc. Then, using that height, his best idea of his longitude, and the Almanac's predicted coordinates of the body he computed (or found in a table) the longitudinal difference between the body and his position.
That gave him the longitude at his estimated latitude.
Later navigators did this procedure twice, each time using a different assumed nearby latitude. That produced two lat/lon fixes which could be marked on a chart; a line through them was the line the navigator was on (or near).
If done again using a body seen in a different direction, the navigator could cross the lines of position on the chart and have an approximation of his position.
i imagine it's reasonably easy to pinpoint the time within a few hours within at least the tropics, but if you get further north or south, it actually is fairly difficult to guestimate the time from the sun alone.
How would you know the local time when at sea?
the time which the vessel presents is the zone time , its the same time of any thing which is placed or sailed in the same zone however the difference between them in position, that mean if there are two ships, one of them on long 15* degree and the other on 20* degree, both of them will have the same time, regardless that they are not on the same longitude !! because both of them sailing in the same zone (zone number 2 in this example) ! so, you can only calculate the zone number by using this method ( using the D.LONG) .
if your vessel’s time & Greenwich time are given .. you can calculate the zone which the ship sailing on, without determine it’s longitude, if you check your video, you can only calculate 15* 30* 45* 90* 105* degrees ! difference 15* degree ( ranges of zones ), you cant calculate if the ship on long 17 for example! this method will be correct only in one case, if the ship sailing on its zone’s middle .. because the time of the zone = the local mean time of the middle of this zone, BUT you cant depend on this idea because you already don’t know where you are :)
What is the local time? Or do you just wait for midday and count west or east from there?
I don't know, sorry. I do know that at 12 noon your shadow will be pointing north if you're in the northern hemisphere.
@@MrJuvefrank that is not always true. If you are on north hemisphere but on south to tropic of cancer, on summer all shadows will point to south
Celestial means using the sky, or bodies in the sky, such as the sun (which is a star), other stars, or the moon. In this case the presenter is using the sun. Latitude may be determined by measuring the angle of Polaris ( the North Star) above the horizon.
How do we know what GMT is if we are thousands of miles from Greenwich??
The ship will carry a highly accurate clock (chronometer) set at GMT. Whoever reads it should know if it's am or pm in England.
Thanks for the video. It was very helpful.
Hello how you calculate the minutes and second
(minutes divided by 60) plus (seconds divided by 3600) plus (hour difference from GMT) all multiplied by 15 to get an exact longitude.
Very Good 🙂
So technically if you knew your lattitude and you took a noon reading at your location, then began to travel you would still be able to know your longitude without using GMT, would that be correct?
Man I’ve been looking into these question to no avail. But you’re absolutely right. You have to calculate true noon while traveling on a ship which requires a device called a sextant. I’m still working on figuring it all out. Haha
What happens when both of the Greenwich and Ships time show 12 o clock whether am and pm and vice versa?
One may wonder in that if Polaris could be used in determining latitude, why can't a particular star, any bright star as the reference point since stars also rise in the east and move westward. That is, set the clock in Greenwich when that particular star is on the meridian much like what's done with the sun. The only difference is the sun is done in daylight while it's nightime with the star. Sidereal noon, for instance.
really well taught thanks
And if the clocks match perfectly, you could be in port at London, or anywhere within that time zone which is a 7 1/2° radius in either direction of port.
So margin of error is never less than 7 1/2° longitude.
Exactly
Timezones are purely political hocum. Local solar time is the true local time used in the video (really local solar position, but time is a close approximation.).
How would you determine your local time if you were lost
at see ?
At noon in your location the sun is at its highest point. Reset your local watch to 12:00 then compare to your other watch set to GMT. You’re OOL if your clock set to GMT is broken, though.
Sailors in the 1600's wouldn't have been able to use this method for determining longitude as they didn't have timepieces that were accurate enough to keep track of GMT. Even in the very early 1700's it wasn't possible. It was only after John Harrison presented his first clock to compete for the longitude prize in the 1730's did it become a real possibility. Even then many years were to pass before he finally presented his 4th attempt which was the watch that was to finally win him the prize.
There were other methods for determining longitude before this, such as using the transit of the moon or the relative position of the moons of Jupiter. I gather the difficulty with these methods come down to taking accurate measurements; these methods are what I was looking for when I ran across this video.
So, according to you, is only the time 1800 wrong? Make yourself hear 1800s and the rest of the video is good.
That was perfectly explained. Reading the book Longitude by Dava Sobel brought me here.
HOW DO YOU CALCULATE LONGITUDE WITHIN A TIME ZONE- ARE YOU ON THE EASTERN OR WESTERN SIDE OF IT OR ARE YOU IN THE MIDDLE?? IS THIS NECESSARY OR EVEN POSSIBLE??
Knowledge of time zones and local time are not required. An observation of local noon and a clock set to GMT is what is used.
There is a problem with this method. If the ship is anchored and is not moving from its current position, the clock continues to move forward. Therefore the clock's difference to GMT is irrelevant to current position of ship.
You have the concept ok but totally screwed up on the details. First off AM/PM are some antique ameture BS, navigation has always used proper 24 hour clock times.
Second is the very common mistake of mis-using GMT. Solar noon on the prime meridian is 0000GMT, 1200 GCT or 1200 UTC. (and GMT stopped being a thing 100 years ago, and the GMT date changes 12 hours before the normal civil date. UTC replaced GCT 53 years ago.)
To acquire a more accurate longitude you will need to include minutes and seconds of time not just the time zone hour, or you may be many 100's of miles off.
Also, you'd need to use noon, or calculate the time using the latitude and sun position.
@@one8576 They are referring to Longitude and how it relates to time, not latitude or body positions.
@@Somethingisntright64 I am talking about how you'd find the time, although there's more to it than I say, like true solar noon versus observed solar noon.
Celestial observations don’t include a clock. How do you use Celestial Observations to calculate the Longitude? Please explain. Thank you.
cannot
If you don't have a clock set to GMT is is almost impossible. However there is a method which is quite a challenge using the angle between the Sun and Moon - providing both can be seen at the same time, not always possible. A number of special charts or tables would have to be available onboard. This method is known as "lunars" and was used by a famous sailor called Joshua Slocum.
Although your previous video of calculation of latitude was correct but this one is not(fully).
GMT was established in 1884 by international meridian conference.
If it were said by you," So, imagine that you are a sailor in the 1800s and....." it would have been correct but you said 1600s or 1700s. Other than that, the video is 100% CORRECT(for the people who said it was wrong).
Keep making these type of videos...
They are very usefull...
-From INDIA.
Im a complete newbie to this but, how can using a clock give us longitude. There is no accounting for bearing, currents and winds. This doesn't make any sense at all.
Look up the definition of longitude and make sure you understand it.
Thanks Seth. Great explanation. I hope your a teacher cause your damn good at it. 👍🏻👍🏻👍🏻
Except you can’t use Polaris south of the equator.
@@guyfournier I believe the seamen managed to use the Southern Cross someway instead...
I don't understand the "degrees" part. However, this was very helpful and clear for what it did cover.
It means that we understand that the Earth is a kind of sphere, so we use sexagesimal system, i.e.: degrees, minutes and seconds, like in a circle.
Oops, what if you’re south of the equator. You basically start off with a little boat going into the Southern Hemisphere, then proceed to say you can use Polaris to determine your position.
Do you see a problem here?
How can latitude be measured in the Southern Hemisphere? Any idea for longitude?
@@jackjones9460 there are a number of stars that can be used depending on your position. You need the nautical almanac and you need more than one celestial body.
@@jackjones9460 there are plenty of other celestial objects to chose from. Learn about celestial navigation, the celestial sphere, the nautical almanac.
I hope im not stupid :)
If i start at GMT and take a a boat or on a plane and fly for 10 hours and look on my clock. If someone cant tell me what timezone im in im lost? AND if they say.. oh its +4 hours, then i already know what timezone im in?
HOW can i determine longitude using celestial observations? like polaris for longitude? This video told me "Your in New York, change your Clock 10 hours to our time... do u know where you are now??" nothing about noon mentioned here?
İf we dont have A watch and we dont know the time in UK
This makes no sense, if I have a clock on the ship set to local time, then I already know where I am. send the ship out to sea where they dont know there local time and this demo fails
I’ll keep it simple for the simple minded on here. Time was determined by an hourglass. This was turned by the officer of the watch every hour. That is how one determined time. Simple…..just like some of you lot.
awesome!!!
How did u know what time is was??? Did u ask the native Americans what time it was here?
thanks for the video...very clear yet simple...can you please help me in understanding RA and Dec and second how to calculate degree of few other stars
I had to watch this video for school
GMT does no longer exist! It is UTC, please!
Doesn't matter for this type of navigation, just as it doesn't matter for the clock in your living room when you want to watch your favourite TV programme!
Seth very good video but you might consider editing the video to also an include and example of when the ship is in the west and local time is in the PM of a certain day and the GMT is in the AM of the next day.
588158 its the same....
In 1492... THEY DIDNT HAVE CLOCKS !!!
@762fullmetal I never heard of such a thing. Can you say the same for the Europeans ?
@@RobertMOdell Clocks that were Accurate at sea weren’t invented until about the 1830’s, in recorded history.
Ok
Aren't you skipping a few steps?
*_💞💞a💞💞_*
Wrong, chronometers were not invented until 18th century, so this method was not used in 15th ,16th century as claimed in the video. Also the video title is wrong as you are not using only celestial measures but a chronometer as well.
No use
boring
agree, this is stupid and trivial. Besides an accurate on board clock/watch for GMT, the other important piece to know on ship is to determine local time. This video seems to trivialize this part, which is not.
Earth is still flat
Most people who give credit to something like what you wrote here died 500 years ago.