How We Solved the Greatest Riddle In Navigation 

Crazy

I feel like you need a link to the Map Men episode on Solving the Longitude as a foot note to this video.

Why did you change the name of your channel?! I liked the earlier one. Bdw, it's NOT Grenich but Greenwich(pronounced as Green Witch)!

Latitude and Longitude puns must be carefully coordinated. 👍🏼

@@manubhatt3 He’s using the American pronunciation. We’re “Two lands separated by one language.”

Why am i not surprised, terrible.

See I told you he got cheated. You are going to receive a lot of flack for not mentioning this in your video.

that's sad but not unexpected

Yeah.... I think two other prizes were also awarded by the Board of Longitude, but it was also basically like pulling teeth to get them, and the total amount paid out was RATHER less than £20,000. One of the main reasons for that reluctance to part with the prize money is likely that the national purse had grown a bit tighter right around that time due to... oh, I can't remember exactly, some wars or other, probably.

Not only was he screwed up with a prize, but after so many years, it wasn't even mentioned on RU-vid. I can imagine how he would feel now

I never knew that was how he measured the speed of light. That is very interesting and must of been bewildering for him to work through.

That's super damn neat

How does one check their "local clock" out at sea? Am I to assume they reset their watch every day at noon? But, if that's the case they would have moved since noon and then no longer be the same time. Maybe I'm missing something.

@@sindikit The short answer is they used sundials. And I imagine sunrise, noon, and sunset would be an easy way to recalibrate for the day (but I honestly don't know what they did in practice). But you are correct. Time and location are fundamentally linked out at sea. Which is why it was so important to establish another reference point (Greenwich / Naval Time) to differentiate the two. That is the problem statement that drove the arms race for a seaworthy clock.

Wouldn't the period change according to the radial velocity, not the distance? If something happens every 1 hour, we'll see it happen every 1 hour, whether it's next door or a light-year away. Its period will only appear to get shorter or longer if the event is moving towards or away from us. Essentially like a Doppler effect, or blue/red-shifting.

map thing men

Thank you, the subject was so familiar I was thinking this video was a reupload

WHEN WHEN WHEN WHEN WHEN

Isnt it like MAP MEN MAP MEN MAP MAP MAP MEN MEN

MAP MAP MEN MEN

I have another book by Sobel: "Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time." It was published in 1996. Perhaps it's an update of the one published in 1995?

@@jpsned I re-read the publication page. The text copyright is 1995. The Introduction copyright, along with the copyright of The Illustrated Longitude is 1998. This goes along with the story as I remember it from around 1998. Dava Sobel first wrote the book as you describe it with that full title and no illustrations. It was very well received in the scientific community, and she was encouraged to produce it with illustrations, which she did. The reason the text copyright is earlier must be because she used the same text from the original book. I first learned of her and the book on a C-Span Book Notes program -- the original one hosted by Brian Lamb. She was the interviewee. She was an elegant lady, as they say, "of a certain age." Within the interview, she described how she learned that her book had made the bestseller list. She had a hobby of ballroom dancing and was enrolled one night in a Fox Trot competition. Right before her performance, a friend brought in a newspaper clipping with the news that her book was on the best seller list. The Fox Trot is a complicated dance, and one she often was nervous about. But after seeing the news of her book, she stepped out onto the dance floor with the thought, "I don't need to worry about this I am an author!" She and her partner won that night's competition. If you liked the first book, I highly recommend this one.

@@jpetemadre2724 I just found my copy and indeed it has no illustrations. (Very cool cover, though, with two circles cut out to show Harrison and his watch on the inside first page!) That's a very nice story about Dava Sobel and the Foxtrot. I took ballroom dancing lessons for a while and the Foxtrot was one of my favorite steps! Eventually I moved on to East Coast Swing and Lindy Hop. I also performed this type of music (I play woodwinds) all through high school, college and beyond, so it was exciting to learn the steps that went along with the music. One thing that was eye opening to me: the music was definitely written to be danced to, as opposed to just listening. The composers and arrangers clearly knew this as dancing to it was effortless--once you knew the steps. 🙂

@@jpsned Very interesting commentary about the music and dance. I've enjoyed this exchange regarding the book, also.

@@jpetemadre2724 Myself as well!

OOO, nicely done.

This is my kind of detailed thinking!

@@besmart I love this video 🥰

@@besmart fancy 🍵 cup of tea very funny 🤭😃

@@besmart great video 👍

@OfficialBeSmart What is the prize ?

Yeah everything from movement, humidity, air pressure, tempature, etc etc can effect all of it. Hell even what your clock is made of matters. Seriously mechanical clocks are just amazing to me. Wish I grew up around watch makers. Ever see how many movements in some are, and how tiny the effin things are?

Not completely true. The special relativistic effect due to the orbital speed which makes the clock appear 7 microsecond a day slower than on earth, is much smaller than the general relativistic effect due to weaker gravity which makes the clock in orbit appear 45 microsecond a day faster than on earth. The net result is that the clocks in the GPS satellites appear to run 38 microseconds a day faster than the clocks in a GPS receiver on earth. However, this time dilation is NOT included in the GPS algorithms, because it has already been corrected pre-launch by setting the clock speed slightly lower (10.22999999543 MHz) so it will produce the expected 10.23 MHz when in orbit. The only thing that the receiver has to do is compensate for the eccentricity of the orbits of the satellites and its own movement (which includes the rotation of the earth).

@@Gerard1971 Interesting! Thanks for the additional info.

@@Gerard1971 I read that GPS satellites compensate for the gravitational field differences over different parts of the earth as they move around. Not sure how true this is. If only for ones of certain accuracy and precision or what, or maybe a fixed offset based on average orbital path instead of "real-time".

@@BenjaminCronce There is the ground segment of several stations that tracks each GPS satellite to verify its health, time and orbital parameters, then they update the satellites with the corrected time, ephemeris (the orbital parameters of each satellite) and the almanac (the state of all the network). Then the receivers downloads the time, ephemeris and almanac to get their own precise location. Also, to speed up things there is A-GPS (Assisted GPS), in which the smartphone can get the ephemeris and/or the almanac from the cellular network or the internet. That's why is faster to find your location when you have cell service than when you don't have coverage for a long time, because the GPS receiver needs more time to get all the data and then estimate its position.

@@EduardoEscarez That's fascinating. GPS might be one of the most complicated and underappreciated technologies we routinely use.

I've been there three times and never heard any of this, but saw some cool boat stuff.

@SteveMcMief - And four of those old clocks at the Royal Observatory are the actual, original H1 through H4 timepieces built by Harrison! H4, his 4th attempt, is the timepiece depicted in this video.

@@stevenemert837 Also worth mentioning that H1, H2 and H3 will normally be running all the time. H4 is only run on occasion. BBC Horizon did an episode many years ago on Harrison. Since then Dava Sobel has published a great book on the subject. There was also two part Channel 4 drama staring Michael Gambon and Jeremy Irons which is excellent and tells parallel stories of the clocks development alongside their repair and refurbishment. One of the reasons that Harrison did not win the full prize was nothing to do with his skill or the clocks and watches he produced, it was because people expected the prize to be finally won by the almanac camp - aka astronomers. Basically, the competition was biased against him from the start.

@@apkk5594 Why was it only run on occasion?

@@Anonymous-df8it unlike the clocks, H4 is not self lubricating. The consequence is that the oil needed to run it will slowly degrade the watch and so they minimise it's use.

I was not... you made me lol

No evidence for aliens?? But, look in a mirror You are an alien, you live on a planet in space, and so would some other beings on a faraway planet in a faraway galaxy So yeah, there is evidence for aliens, you are one.

That is because of race-i.s.t anthropologists.

@@ws6778 Wait what if Ancient Aliens... Them Sudanese Green Card Workers stealing jobs from Real Hard Working Egyptian Citizens. /s [For those that do not get the joke Sudan has more pyramids - just smaller and different slope angles]

@@ws6778 Those furrys of the poles really like to drive against each other in tracks at high speeds huh?

good point! aliens have taken over the miracle business.

A star map is the most accurate way but there are other ways like magnetic field or sun/earth sensors. I'm a satellite engineer

How fortunate you are to have those knowlegeable ancesters.

In the USA anyway.

Yes, but if you go to 7 degrees longitude, the time will be the same as the time in Greenwich, so you still don't know where you are!

@@Anonymous-df8it No. At 7 degrees longitude your sundial will give you a time that is almost half an hour earlier than your clock set to Greenwich time. You can use that difference to calculate where you are.

@@neuralnetwork17 Aren't sundials wrong due to the equation of time though?

@@Anonymous-df8it I wouldn't call the sundial wrong. I am of the (minority) opinion that apparent solar time is the "real" time. 😆 But you're right, the length of the day does vary, and if you don't account for that you have a margin of error of about three degrees. Luckily, people have known about this for millennia, and accurate tables for accounting for this have been available since the 17th century. And even if you don't have those it is extremely useful to be able to determine your approximate longitude to a few degrees rather than not at all.

@@neuralnetwork17 Why do you need tables? Couldn't they come up with a formula that approximates the equation of time?

Oh the prize was paid, but only after the intervention of the monarch. Harrison died a wealthy man.

they sacrificed a child and waited for it to rain. then that’s 3pm.

It is accurate when you use a sextant.

@@stocktonnash YES

As far as I know you make several measurements (with a sextant) before and after noon. Problem is movement (not good on a ship), but it works on land (astronomers did it "back then") …

I don't think so. Timezones don't make any sense far away from Earth. I think we'll use some distant, periodic event, like a pulsar or something.

Some stratum 0 time servers get their time from GPS.

As far as I understand it, the timing signals from GPS satellites are critical for actually computing your location, so I think they're used every single time you use your phone's location services. My assumption is that the use of GPS time for stratum 0 ntp servers is a clever re-use of data already present in the signal for another purpose.

I was more disappointed that the clocks also have to take into account the relativistic speeds they are traveling (not near c, but it's enough, and their altitude is also messing with the effects of gravity on time.

You only need 3 signals if you already either know your altitude or have accurate topographic data (and assume you are on the surface of the planet).

@@eliljeho Yes, both special and general relativity affect the timekeeping between the sattelites and the earth's surface.

@@timseguine2 That is right, your altitude information basically solves/gets rid of one variable. However, I wonder how you can get Your GPS to know the altitude. Or is that only a feature on some devices?

@@andor_yoko As far as I know, the GPS units that support it assume mean sea level, which is a fairly crude approximation.

First reply

Last reply

Thats Voltron

Is pretty cool

@@SANDWICHvanquish Thanks! Really appreciate it. I recognized it from somewhere, but couldn't remember which show

@@Maybachdemon your welcome happy to help ^_^

Shh no one will notice Yugoslavia

@@besmart first big tik toker that's funny 🤭😃

Yeah, I also had the same question. The only way I can think of doing it is to use another clock and set it to noon. Since presumably noon would be where the sun is highest in the sky. But that might not be the right answer.

Sailors could calculate local time based on the suns position with a sundial or also from the position of the moon, pretty accurately. But the video doesnt make that part very clear.

by measuring the position of the sun with a sextant.

@@nulious sextant was invented in 1759 so they didnt exist in the period that the video is about.

@@brando8997 before the sextant they used an astrolabe

i guess theyd know the longitude just before entering the fog, and then they could estimate it further based on their trajectory which theyd know with a compass maybe? 12 days still feels like a stretch though. Also latitude would be difficult in a fog without access to view the north star.

local time is set by measuring the position of the sun with a sextant.

@@orsonmoniz exactly this was their problem in that example, they lost track and had way too big error

@@nulious yeah, if you can see the sun

We gotta make sure to call out Joe if we no longer spot Globey in the background for future videos 😂🌎

It's enough to know that it kept precise (enough for those times) time while at sea. How exactly it worked is a topic for a separate video.

If you want a video about advanced metallurgy and spring technology you'll have to go somewhere else, friend 😂

This is not totally scientific, but briefly, Harrison had already built extremely accurate (for his time and even later) land-based clocks. His experience as a carpenter using different woods helped; he realized a big problem was that metals, including steel, expand and contract with temperature fluctuations, distorting the timepiece parts. He was able to come up with a way to compensate. He also found a way to "cushion" his clocks and chronometers for use at sea from the movement of the ship on the waves. He was a very intelligent man, and his common sense and inquiring mind proved to be more useful than the university studies of the experts who were trying to refine the tables that were the competing and more prestigious system. I think he must have had a Darwinian type of mind, making observation primary and basing theories on actual facts. And, of course, having endless patience to keep experimenting over decades. One interesting point: a patron of Harrison was able to gain the interest of George III, who was fascinated by clockwork and automatons. This king tends to get dismissed as mad and/or a tyrant, but in fact, in the early part of his reign, was fairly enlightened as far as science and the arts were concerned. His interest and even help was useful to Harrison.

@@besmart cool video 😎

It's about time! :P