5 ms·

Tides are weirder than you think

172 points by surprisetalk 11mo ago

fhdkweig 11mo ago
https://www.youtube.com/watch?v=AxC770lpSLw https://www.youtube.com/watch?v=AxC770lpSLw shows one of the old tide prediction mechanical computers briefly mentioned in this article. It is effectively doing an inverse Fourier Transform, summing all the various 30+ sinusoids that affect the tides.
wasting_time 11mo ago
Relevant xkcd: https://xkcd.com/3135 https://xkcd.com/3135
- santoriv 11mo ago
  Reminds me of the time that Bill O'Reilly argued on national television that tides were inexplicable. https://www.youtube.com/watch?v=NUeybwTMeWo https://www.youtube.com/watch?v=NUeybwTMeWo
- boothby 11mo ago
  I live near a river that flows backwards for some 50km or so with tides. The first time I saw it, I thought I'd gotten turned around because surely water can't flow uphill, right? It's fun to find out that one is so wrong about basic physics.
- deleted 11mo ago
  [deleted]
xg15 11mo ago
> Kelvin’s machine automates the second half of that task. As the pulleys spin, they pull on a common chain by the correct amount for each of the calculated components. A year’s worth of tidal tables can be put together in half an hour, if you know the components. Even better, you can “guess and check” the components by comparing your machine’s output to past records, and adjusting the pulleys until you get something that works correctly. I didn't know they already had machine learning and model fitting algorithms in the 1800s, but here we are...
- LoganDark 11mo ago
  https://xkcd.com/1838 https://xkcd.com/1838
  - B1FF_PSUVM 11mo ago
    Sometimes we need dates attached - by the numbers (1838 of current 3176) that's probably some 5 or 6 years before ChatGTP. Or 3 or 4 years after the Netflix challenge.
    - eesmith 11mo ago
      No later than 17 May 2017 - https://www.explainxkcd.com/wiki/index.php/1838:_Machine_Learning https://www.explainxkcd.com/wiki/index.php/1838:_Machine_Lea...
  - thunderbong 11mo ago
    Mobile view https://m.xkcd.com/1838/ https://m.xkcd.com/1838/
- srean 11mo ago
  https://news.ycombinator.com/item?id=44066091 https://news.ycombinator.com/item?id=44066091
metalman 11mo ago
out the back door of my house, down through the field and woods to the water is a 12 min walk at high tide, and another 12 min + walk to the water at low tide, 53 vertical feet between the two. I know ,not the slightest thing about tides, other than what my senses tell me when walking the shore, and I suppose the practicalities of beach walking along cliffs are similar to planning and predicting arival times for ships loaded to the maximum draft, the money to be made there bieng the motivation behind the push to understand tides.
- ttoinou 11mo ago
  That seems huge. Are you in Fundy’s bay in Canada?
  - metalman 11mo ago
    huge, and where else? there are some places here where the slope is so gradual, that the low tide is over the horison growing up we had a camp right at the end of Burnt Coat Head, in Noel, and never did make it to the low tide line between there and Cape Split there is the full range of tidal phenominon on display, resonant standing waves, whirlpools, tidal bores(with surfing black ducks),whole bays emptied, and varios dikes and berms, dams, locks, to hold it back there are one ot two other places on the planet that are close, and from the charts in the article, spots with NO tide, which when I think about,is very wierd indeed
antognini 11mo ago
You may have seen diagrams of the tidal force of the Moon on the earth (like this one: https://www.oc.nps.edu/nom/day1/tide_force_diagram.gif https://www.oc.nps.edu/nom/day1/tide_force_diagram.gif). Intuitively you would think that the tide is being formed because the Moon is "lifting up" the water at the point closest to the Moon. But this contribution is actually very miniscule to the tidal effect. Instead the bulk of the tides are produced about 45 degrees away where the tidal force is parallel to the Earth's surface. This has the effect of dragging the water closer to the tidal bulge.
- fsckboy 11mo ago
  but to develop better intuition, think of the sun's gravity as a field in space and nothing is being dragged anywhere, it's just that wherever you are feels appropriate to where you are and where you are going is the path of least resistance, and the places around you feel the same way, and where you all are in relation to each other (in this field) changes its relative position to everything else. the water of an incoming tide doesn't feel "i'm being dragged uphill", it feels "hey, the earth is moving underneath me". it's all in freefall all the time. you don't feel like you are rotating at 1000 mph (1600 kph) but you do feel your weight against the surface of the earth. same with the water, except it feels itself being squeezed by everything around it like you only feel that in the entrance to a crowded venue. so, the water on the side toward the moon and the water on the side away from the moon would mostly perceive the earth as dropping away or coming closer (if they could perceive anything at all) where they are is always their point of reference
- mcswell 11mo ago
  Thank you--the diagram you link is a better explanation of whey the tide "bulges up on the sides of the Earth closest to and farthest from the Moon"--the article left this entirely unclear. In particular, I could understand how two satellites connected by a cable would result in the cable being stretched. But I still find it hard to wrap my mind around the fact that we get a high tide where the Earth's gravity and the Moon's add (the far side of the Earth from the Moon), but we also get a high tide on the opposite side, where the Moon's gravitational pull is subtracted from the Earth's. The centrifugal force is (I think) a much better explanation. (I realize physicists don't consider that a force, but...) So yes, tides really are weirder than I think. (The other facts in the article were actually familiar, e.g. the fact that the tides in Hawaii are quite small, because it's not far from an amphidromic point.)
esafak 11mo ago
https://en.wikipedia.org/wiki/Tide-predicting_machine https://en.wikipedia.org/wiki/Tide-predicting_machine Basically, a summation of sinusoids.
cortesoft 11mo ago
I know this is unrelated to the actual content, but I have such a visceral reaction to any headline in the "x is different than you think"... how do you know what I think? I am sure many people who read this will be experts on tides, and the title is completely wrong. For me, the worst are posts about scale and things I won't need, like "You don't need kafka" or "your data isn't actually big data" or "don't horizontally scale, just get a bigger server" I get that I am not the target audience and there are people for whom those statements are true, but I am running Kafka clusters with data from 10s of thousands of servers, I absolutely can't move that to a single machine. I wish they would phrase it as "Tides are weirder than most people think", although that probably doesn't drive as much engagement.
- renewiltord 11mo ago
  It is property of English language where "you" is used in place of "one" very often. This is particularly common in American English which has less formality to it; less Frenchiness. No 'on' etc. Everyone is 'tu'. It is language quirk, but you can probably use LLM to replace HN headlines like this. Pretty cheap and one will no longer have visceral reaction that one does not wish.
  - panxyh 11mo ago
    Most people might think that someone doesn't need LLM for that.
    - renewiltord 11mo ago
      Most people don’t have visceral reaction. The world is full of tools. You can bend your experience of it to your will.
- nephihaha 11mo ago
  Because if someone says "one" it sounds affected.
  - cwmoore 11mo ago
relwin 11mo ago
We have a "King Tide" today in SoCal where the local swing is +7/-1.5. Get to see normally hidden tidepools and a bunch of cobbles...
johnea 11mo ago
Nice article! Any talk of tide prediction should always mention xtide: https://flaterco.com/xtide/ https://flaterco.com/xtide/ I've used it with great accuracy in a number of locations around the world. Another one of those free software packages that's been meticulously maintained by one person for decades...
- 2b3a51 11mo ago
  Here we go (quote from the xtide Web page) "Q: I live outside of the U.S. and my location is no longer supported. What happened? A: Many data were purged after a legal threat from the U.K. Hydrographic Office (UKHO) in January 2001. I ended maintenance of the non-U.S. data that replaced them for different reasons in early 2012." I wonder how much money the Hydrographic Office saved by not allowing this data to be distributed?
o4c 11mo ago
Veritasium made a great video on Kelvin's Tide-predicting machine in 2021. Title: The Most Powerful Computers You've Never Heard Of URL: https://www.youtube.com/watch?v=IgF3OX8nT0w https://www.youtube.com/watch?v=IgF3OX8nT0w
themafia 11mo ago
> When they’re least lined up (First and Last Quarter Moon), tides are more smoothed out. This is a “Neap Tide”. And when they're the "most lined up" you get the "King Tide." https://en.wikipedia.org/wiki/King_tide https://en.wikipedia.org/wiki/King_tide
- pea 11mo ago
  We had one of these today in Sausalito!
srean 11mo ago
Relevant https://news.ycombinator.com/item?id=44065458 https://news.ycombinator.com/item?id=44065458 (92 comments) Also https://content.teachastronomy.com/taweb/images/textbook/hrthumbs/d13bb5d5f1856a0e38f838ab661b16fd1217c6ba.png https://content.teachastronomy.com/taweb/images/textbook/hrt... Inlining my comment that I had posted there: The problem of predicting tides was so important that it attracted many Physics and Maths heavy weights. You can well imagine how important predicting tides would have been for D-day landing. One related fascinating historical artifact is the special purpose analogue computer designed by Lord Kelvin in the 1860s based on Fourier series, harmonic analysis. Think difference engine in it's cogs and cams glory, but special purpose. https://en.m.wikipedia.org/wiki/Tide-predicting_machine https://en.m.wikipedia.org/wiki/Tide-predicting_machine Possibly one of the first examples of Machine learning, with Machine in capital 'M'. It incorporated recent tidal observations to update it's prediction. Note that sinusoids are universal approximators for a large class of functions, an honour that is by no means restricted to deep neural nets. George Darwin (Charles Darwin's son) was a significant contributor in the design and upgrade of the machine. https://en.m.wikipedia.org/wiki/George_Darwin https://en.m.wikipedia.org/wiki/George_Darwin Other recognizable names who worked on tide prediction problem were Thomas Young (of double slit experiment fame) and Sir George Airy (of Airy disk fame).
globular-toast 11mo ago
I see I'm not the only geek fascinated by the tide. I knew all the stuff in the article already, of course. It seems it's like railways or something, seems to trigger something in geeky brains. I live in the UK so see some of the largest "swings" in the world. It never ceases to amaze me that it all happens in the space of 6 hours. I've also gone to see spring tides just to see what it looks like. It's cool, and scary.
nrhrjrjrjtntbt 11mo ago
Tides. The OG gravitational wave detectors.
- layer8 11mo ago
  Tides are gravitational waves, as it were.
geokon 11mo ago
This explanation is a lot more thorough and detailed (and there are no tidal bulges.. Common myth) https://physics.stackexchange.com/questions/121830/does-earth-really-have-two-high-tide-bulges-on-opposite-sides https://physics.stackexchange.com/questions/121830/does-eart...
- hyttioaoa 11mo ago
  I went down a rabbit hole a few weeks back to discover this. I was so upset with so many wrong explanations including Neil de Grasse Tyson saying we're moving into the bulges. it's very magical though discovering the beauty of it.
- B1FF_PSUVM 11mo ago
  What really gets me is the "Map of the strength of the 12-hr lunar tide" in the Layer 4 section of the article posted, which I haven't seen discussed. All the rest is swept away, and you have stretches of coastline with tides over one meter, and others with nearly zero, just because of landmass distribution ... If you moved Miami Beach to the French Atlantic coast, things would get interesting.
- deleted 11mo ago
  [deleted]
mycall 11mo ago
Odd weather wasn't mentioned. While weather does not create tides, but it can significantly modify the actual water level compared with the purely astronomical tide that the article describes.
fmjrey 11mo ago
Jeanne Rousseau, who passed away in 2012, asked in an interview [1]: Why are the syzygy tidal coefficients equal when the quadrature tidal coefficients are at opposite extremes? Why are the syzygy coefficients at opposite extremes when the others are equal? Who can explain this using the laws of universal gravitation? Her point is that you can't. Earlier in that interview she says: I was put in touch with the Institut de Physique du Globe [2]. In April 1953, I met with Professor Coulomb [3], who was the director at the time, and asked him about the ionic variations that might occur during the lunar phases. His formal response was that there were none. However, I had already been observing them for some time. I must say that in 1953 I had already begun to observe the phenomenon of the tides. Being told that, apart from a minimum of atmospheric ionization at 4 a.m., there is nothing else that can have an impact on the biological, human, or other levels, I said: but there is the phenomenon of the tides! And that's when I got this response, which marked a break with the scientific community for me: The phenomenon of the tides is a phenomenon that is beyond us. We waste our time when we take an interest in phenomena that are beyond us. If you don't want to waste yours, focus on other things. Jeanne Rousseau demonstrated through observation that tidal phenomena are not solely gravitational but primarily electromagnetic. One can read more about this in English in this paper [4]. [1] https://youtu.be/ytWerrYTBLs https://youtu.be/ytWerrYTBLs [2] https://en.wikipedia.org/wiki/Institut_de_Physique_du_Globe_de_Paris https://en.wikipedia.org/wiki/Institut_de_Physique_du_Globe_... [3] https://en.wikipedia.org/wiki/Jean_Coulomb https://en.wikipedia.org/wiki/Jean_Coulomb [4] https://www.researchgate.net/publication/384443419_Cosmic_Resonances https://www.researchgate.net/publication/384443419_Cosmic_Re...
- typicalset 11mo ago
  This is, not to put too fine a point on it, crank science. Opening up the linked document, the DOI fails to resolve, the paper investigates pH variations in urine during tide cycles, and also skimming over it doesn't appear to make a single prediction. This is at best unfalsifiable, and a "break with the scientific community" is an accurate assessment. The physics of tides is largely well-understood, and the moon and sun provide the primary forcing. Accurate tide tables are regularly computed the world over, with measurements regularly made. Without even looking at measurements, the shipping industry demands accurate tide forecasts for navigating efficiently. The claim that "tidal phenomena are... primarily electromagnetic" requires some serious evidence to back it up, with calculates to boot, rather than invoking mysticism that tides are "beyond us". Many things are beyond our current scientific understanding, and that is humbling, but tides are quite well understood.
bmitch3020 11mo ago
A detail not included here, but important for people interested in the sea level, is the effects of the wind. Lots of places along the east coast of the US experience mild tides, but a steady wind in the right direction will push sea levels up in various bays and inlets. The storm surge of a hurricane turns it up to 11.
vax425 11mo ago
I know! It took most of this summer to get my tide clock to predict accurately, using NOAA harmonic constituents data crammed into an Arduino, a GPS module, and published formulas. Take a look: https://digitalhorology.etsy.com/listing/4345582508 https://digitalhorology.etsy.com/listing/4345582508
teleforce 11mo ago
Reading most of the technology articles would have you to believe that dark ages really existed and for more than thousands years, i.e from Greece to Renaissance time there is no marine technology advancement between them. The truth of the matter is that the Arabic and muslim are the master of the sea during this so called "dark ages" time, and many advancement has been made from navigation gear of the Arabic astrolobe to the Idrisi map. In tide prediction Al-Kindi for example, has notable work on tides in his seminal book Treatise on the Efficient Cause of the Flow and Ebb back in 9th CE [1],[2]. [1]al-Kindi: https://en.wikipedia.org/wiki/Al-Kindi https://en.wikipedia.org/wiki/Al-Kindi [2] Al-Kindi: https://muslimheritage.com/al-kindi/ https://muslimheritage.com/al-kindi/
- eesmith 11mo ago
  From [1] > In a treatise entitled as Risala fi l-Illa al-Failali l-Madd wa l-Fazr (Treatise on the Efficient Cause of the Flow and Ebb), al-Kindi presents a theory on tides which "depends on the changes which take place in bodies owing to the rise and fall of temperature."
  - teleforce 11mo ago
    Thanks for pointing that out but there's must some mistakes on the website. Al-Kindi contribution is on the experiment in showing that tides are caused by the expansion of water due to heat but of course later people know that it mainly due to gravity. Other well known Arabic and muslim reseachers in the middle ages working on ocean tides are Abu Ma'shar al-Balkhi (Albumasar), Al-Biruni and Nur ad-Din al-Bitruji (Alpetragius). Albumasar in his seminal book on tides was the first hypothesized the lunar correlation [1]. He's arguably the most important figure in the history of tidal theory between the ancient Greeks and Renaissance. His famous work namely The Great Introduction to Astrology (Kitab al-Madkhal al-Kabir) was translated into Latin in the 12th century and became the standard reference for European scholars (like Roger Bacon and Albert the Great) when they tried to understand tidal physics. Al-Biruni was a polymath who had direct experience with the strong tides of the Indian Ocean specifically at the port of Somnath in Gujarat, India. Of the 146 books written by him, 95 are devoted to astronomy, mathematics, and related subjects like mathematical geography [2]. In his encyclopedic work Indica (Kitab al-Hind), he discussed how the moon influences "moist substances". He dismissed the common myth in the region that viewed tides as the breathing of the earth or sea monsters. He firmly established the moon as the physical cause of the tidal cycle. This observation was using data gathered from sailors and his own measurements of the shoreline. Al-Bitruji was the very first astronomer who proposed an alternative to Ptolemy's model of the universe long before (more than 300 years) Galileo, by avoiding both epicycles and eccentrics mechanism [3]. According to him, the movement of the celestial spheres created a physical dragging force that stirred the waters of the earth, but his theory is less accurate than Albumasar's. Ocean tides was a significant area of study for Arab and Muslim reseachers during the middle ages (Islamic Golden Age), had extensive access to the Persian Gulf, the Red Sea, and the Indian Ocean, where tides are far more dramatic. The Greeks and Romans however, had a very limited exposure to ocean tides since they mostly observing the tide-less Mediterranean sea. [1] Abu Ma'shar al-Balkhi: https://en.wikipedia.org/wiki/Abu_Ma%27shar_al-Balkhi https://en.wikipedia.org/wiki/Abu_Ma%27shar_al-Balkhi [2] Al-Biruni: https://en.wikipedia.org/wiki/Al-Biruni https://en.wikipedia.org/wiki/Al-Biruni [3] Nur ad-Din al-Bitruji: https://en.wikipedia.org/wiki/Nur_ad-Din_al-Bitruji https://en.wikipedia.org/wiki/Nur_ad-Din_al-Bitruji
ljgfxxxxxth 11mo ago
All of these explanations are talking about “pulling” from gravity. What they should really be saying is that spacetime is being affected as the moon orbits.

172 points by surprisetalk 11mo ago

https://www.youtube.com/watch?v=AxC770lpSLw https://www.youtube.com/watch?v=AxC770lpSLw shows one of the old tide prediction mechanical computers briefly mentioned in this article. It is effectively doing an inverse Fourier Transform, summing all the various 30+ sinusoids that affect the tides.

wasting_time 11mo ago

Relevant xkcd: https://xkcd.com/3135 https://xkcd.com/3135

santoriv 11mo ago
Reminds me of the time that Bill O'Reilly argued on national television that tides were inexplicable. https://www.youtube.com/watch?v=NUeybwTMeWo https://www.youtube.com/watch?v=NUeybwTMeWo
boothby 11mo ago
I live near a river that flows backwards for some 50km or so with tides. The first time I saw it, I thought I'd gotten turned around because surely water can't flow uphill, right? It's fun to find out that one is so wrong about basic physics.
deleted 11mo ago
[deleted]

xg15 11mo ago

> Kelvin’s machine automates the second half of that task. As the pulleys spin, they pull on a common chain by the correct amount for each of the calculated components. A year’s worth of tidal tables can be put together in half an hour, if you know the components. Even better, you can “guess and check” the components by comparing your machine’s output to past records, and adjusting the pulleys until you get something that works correctly. I didn't know they already had machine learning and model fitting algorithms in the 1800s, but here we are...

LoganDark 11mo ago
https://xkcd.com/1838 https://xkcd.com/1838
- B1FF_PSUVM 11mo ago
  Sometimes we need dates attached - by the numbers (1838 of current 3176) that's probably some 5 or 6 years before ChatGTP. Or 3 or 4 years after the Netflix challenge.
  - eesmith 11mo ago
    No later than 17 May 2017 - https://www.explainxkcd.com/wiki/index.php/1838:_Machine_Learning https://www.explainxkcd.com/wiki/index.php/1838:_Machine_Lea...
- thunderbong 11mo ago
  Mobile view https://m.xkcd.com/1838/ https://m.xkcd.com/1838/
srean 11mo ago
https://news.ycombinator.com/item?id=44066091 https://news.ycombinator.com/item?id=44066091

metalman 11mo ago

out the back door of my house, down through the field and woods to the water is a 12 min walk at high tide, and another 12 min + walk to the water at low tide, 53 vertical feet between the two. I know ,not the slightest thing about tides, other than what my senses tell me when walking the shore, and I suppose the practicalities of beach walking along cliffs are similar to planning and predicting arival times for ships loaded to the maximum draft, the money to be made there bieng the motivation behind the push to understand tides.

ttoinou 11mo ago
That seems huge. Are you in Fundy’s bay in Canada?
- metalman 11mo ago
  huge, and where else? there are some places here where the slope is so gradual, that the low tide is over the horison growing up we had a camp right at the end of Burnt Coat Head, in Noel, and never did make it to the low tide line between there and Cape Split there is the full range of tidal phenominon on display, resonant standing waves, whirlpools, tidal bores(with surfing black ducks),whole bays emptied, and varios dikes and berms, dams, locks, to hold it back there are one ot two other places on the planet that are close, and from the charts in the article, spots with NO tide, which when I think about,is very wierd indeed

antognini 11mo ago

You may have seen diagrams of the tidal force of the Moon on the earth (like this one: https://www.oc.nps.edu/nom/day1/tide_force_diagram.gif https://www.oc.nps.edu/nom/day1/tide_force_diagram.gif). Intuitively you would think that the tide is being formed because the Moon is "lifting up" the water at the point closest to the Moon. But this contribution is actually very miniscule to the tidal effect. Instead the bulk of the tides are produced about 45 degrees away where the tidal force is parallel to the Earth's surface. This has the effect of dragging the water closer to the tidal bulge.

fsckboy 11mo ago
but to develop better intuition, think of the sun's gravity as a field in space and nothing is being dragged anywhere, it's just that wherever you are feels appropriate to where you are and where you are going is the path of least resistance, and the places around you feel the same way, and where you all are in relation to each other (in this field) changes its relative position to everything else. the water of an incoming tide doesn't feel "i'm being dragged uphill", it feels "hey, the earth is moving underneath me". it's all in freefall all the time. you don't feel like you are rotating at 1000 mph (1600 kph) but you do feel your weight against the surface of the earth. same with the water, except it feels itself being squeezed by everything around it like you only feel that in the entrance to a crowded venue. so, the water on the side toward the moon and the water on the side away from the moon would mostly perceive the earth as dropping away or coming closer (if they could perceive anything at all) where they are is always their point of reference
mcswell 11mo ago
Thank you--the diagram you link is a better explanation of whey the tide "bulges up on the sides of the Earth closest to and farthest from the Moon"--the article left this entirely unclear. In particular, I could understand how two satellites connected by a cable would result in the cable being stretched. But I still find it hard to wrap my mind around the fact that we get a high tide where the Earth's gravity and the Moon's add (the far side of the Earth from the Moon), but we also get a high tide on the opposite side, where the Moon's gravitational pull is subtracted from the Earth's. The centrifugal force is (I think) a much better explanation. (I realize physicists don't consider that a force, but...) So yes, tides really are weirder than I think. (The other facts in the article were actually familiar, e.g. the fact that the tides in Hawaii are quite small, because it's not far from an amphidromic point.)

esafak 11mo ago

https://en.wikipedia.org/wiki/Tide-predicting_machine https://en.wikipedia.org/wiki/Tide-predicting_machine Basically, a summation of sinusoids.

cortesoft 11mo ago

I know this is unrelated to the actual content, but I have such a visceral reaction to any headline in the "x is different than you think"... how do you know what I think? I am sure many people who read this will be experts on tides, and the title is completely wrong. For me, the worst are posts about scale and things I won't need, like "You don't need kafka" or "your data isn't actually big data" or "don't horizontally scale, just get a bigger server" I get that I am not the target audience and there are people for whom those statements are true, but I am running Kafka clusters with data from 10s of thousands of servers, I absolutely can't move that to a single machine. I wish they would phrase it as "Tides are weirder than most people think", although that probably doesn't drive as much engagement.

renewiltord 11mo ago
It is property of English language where "you" is used in place of "one" very often. This is particularly common in American English which has less formality to it; less Frenchiness. No 'on' etc. Everyone is 'tu'. It is language quirk, but you can probably use LLM to replace HN headlines like this. Pretty cheap and one will no longer have visceral reaction that one does not wish.
- panxyh 11mo ago
  Most people might think that someone doesn't need LLM for that.
  - renewiltord 11mo ago
    Most people don’t have visceral reaction. The world is full of tools. You can bend your experience of it to your will.
nephihaha 11mo ago
Because if someone says "one" it sounds affected.
- cwmoore 11mo ago

relwin 11mo ago

We have a "King Tide" today in SoCal where the local swing is +7/-1.5. Get to see normally hidden tidepools and a bunch of cobbles...

johnea 11mo ago

Nice article! Any talk of tide prediction should always mention xtide: https://flaterco.com/xtide/ https://flaterco.com/xtide/ I've used it with great accuracy in a number of locations around the world. Another one of those free software packages that's been meticulously maintained by one person for decades...

2b3a51 11mo ago
Here we go (quote from the xtide Web page) "Q: I live outside of the U.S. and my location is no longer supported. What happened? A: Many data were purged after a legal threat from the U.K. Hydrographic Office (UKHO) in January 2001. I ended maintenance of the non-U.S. data that replaced them for different reasons in early 2012." I wonder how much money the Hydrographic Office saved by not allowing this data to be distributed?

o4c 11mo ago

Veritasium made a great video on Kelvin's Tide-predicting machine in 2021. Title: The Most Powerful Computers You've Never Heard Of URL: https://www.youtube.com/watch?v=IgF3OX8nT0w https://www.youtube.com/watch?v=IgF3OX8nT0w

themafia 11mo ago

> When they’re least lined up (First and Last Quarter Moon), tides are more smoothed out. This is a “Neap Tide”. And when they're the "most lined up" you get the "King Tide." https://en.wikipedia.org/wiki/King_tide https://en.wikipedia.org/wiki/King_tide

pea 11mo ago
We had one of these today in Sausalito!

srean 11mo ago

Relevant https://news.ycombinator.com/item?id=44065458 https://news.ycombinator.com/item?id=44065458 (92 comments) Also https://content.teachastronomy.com/taweb/images/textbook/hrthumbs/d13bb5d5f1856a0e38f838ab661b16fd1217c6ba.png https://content.teachastronomy.com/taweb/images/textbook/hrt... Inlining my comment that I had posted there: The problem of predicting tides was so important that it attracted many Physics and Maths heavy weights. You can well imagine how important predicting tides would have been for D-day landing. One related fascinating historical artifact is the special purpose analogue computer designed by Lord Kelvin in the 1860s based on Fourier series, harmonic analysis. Think difference engine in it's cogs and cams glory, but special purpose. https://en.m.wikipedia.org/wiki/Tide-predicting_machine https://en.m.wikipedia.org/wiki/Tide-predicting_machine Possibly one of the first examples of Machine learning, with Machine in capital 'M'. It incorporated recent tidal observations to update it's prediction. Note that sinusoids are universal approximators for a large class of functions, an honour that is by no means restricted to deep neural nets. George Darwin (Charles Darwin's son) was a significant contributor in the design and upgrade of the machine. https://en.m.wikipedia.org/wiki/George_Darwin https://en.m.wikipedia.org/wiki/George_Darwin Other recognizable names who worked on tide prediction problem were Thomas Young (of double slit experiment fame) and Sir George Airy (of Airy disk fame).

globular-toast 11mo ago

I see I'm not the only geek fascinated by the tide. I knew all the stuff in the article already, of course. It seems it's like railways or something, seems to trigger something in geeky brains. I live in the UK so see some of the largest "swings" in the world. It never ceases to amaze me that it all happens in the space of 6 hours. I've also gone to see spring tides just to see what it looks like. It's cool, and scary.

nrhrjrjrjtntbt 11mo ago

Tides. The OG gravitational wave detectors.

layer8 11mo ago
Tides are gravitational waves, as it were.

geokon 11mo ago

This explanation is a lot more thorough and detailed (and there are no tidal bulges.. Common myth) https://physics.stackexchange.com/questions/121830/does-earth-really-have-two-high-tide-bulges-on-opposite-sides https://physics.stackexchange.com/questions/121830/does-eart...

hyttioaoa 11mo ago
I went down a rabbit hole a few weeks back to discover this. I was so upset with so many wrong explanations including Neil de Grasse Tyson saying we're moving into the bulges. it's very magical though discovering the beauty of it.
B1FF_PSUVM 11mo ago
What really gets me is the "Map of the strength of the 12-hr lunar tide" in the Layer 4 section of the article posted, which I haven't seen discussed. All the rest is swept away, and you have stretches of coastline with tides over one meter, and others with nearly zero, just because of landmass distribution ... If you moved Miami Beach to the French Atlantic coast, things would get interesting.
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mycall 11mo ago

Odd weather wasn't mentioned. While weather does not create tides, but it can significantly modify the actual water level compared with the purely astronomical tide that the article describes.

fmjrey 11mo ago

Jeanne Rousseau, who passed away in 2012, asked in an interview [1]: Why are the syzygy tidal coefficients equal when the quadrature tidal coefficients are at opposite extremes? Why are the syzygy coefficients at opposite extremes when the others are equal? Who can explain this using the laws of universal gravitation? Her point is that you can't. Earlier in that interview she says: I was put in touch with the Institut de Physique du Globe [2]. In April 1953, I met with Professor Coulomb [3], who was the director at the time, and asked him about the ionic variations that might occur during the lunar phases. His formal response was that there were none. However, I had already been observing them for some time. I must say that in 1953 I had already begun to observe the phenomenon of the tides. Being told that, apart from a minimum of atmospheric ionization at 4 a.m., there is nothing else that can have an impact on the biological, human, or other levels, I said: but there is the phenomenon of the tides! And that's when I got this response, which marked a break with the scientific community for me: The phenomenon of the tides is a phenomenon that is beyond us. We waste our time when we take an interest in phenomena that are beyond us. If you don't want to waste yours, focus on other things. Jeanne Rousseau demonstrated through observation that tidal phenomena are not solely gravitational but primarily electromagnetic. One can read more about this in English in this paper [4]. [1] https://youtu.be/ytWerrYTBLs https://youtu.be/ytWerrYTBLs [2] https://en.wikipedia.org/wiki/Institut_de_Physique_du_Globe_de_Paris https://en.wikipedia.org/wiki/Institut_de_Physique_du_Globe_... [3] https://en.wikipedia.org/wiki/Jean_Coulomb https://en.wikipedia.org/wiki/Jean_Coulomb [4] https://www.researchgate.net/publication/384443419_Cosmic_Resonances https://www.researchgate.net/publication/384443419_Cosmic_Re...

typicalset 11mo ago
This is, not to put too fine a point on it, crank science. Opening up the linked document, the DOI fails to resolve, the paper investigates pH variations in urine during tide cycles, and also skimming over it doesn't appear to make a single prediction. This is at best unfalsifiable, and a "break with the scientific community" is an accurate assessment. The physics of tides is largely well-understood, and the moon and sun provide the primary forcing. Accurate tide tables are regularly computed the world over, with measurements regularly made. Without even looking at measurements, the shipping industry demands accurate tide forecasts for navigating efficiently. The claim that "tidal phenomena are... primarily electromagnetic" requires some serious evidence to back it up, with calculates to boot, rather than invoking mysticism that tides are "beyond us". Many things are beyond our current scientific understanding, and that is humbling, but tides are quite well understood.

bmitch3020 11mo ago

A detail not included here, but important for people interested in the sea level, is the effects of the wind. Lots of places along the east coast of the US experience mild tides, but a steady wind in the right direction will push sea levels up in various bays and inlets. The storm surge of a hurricane turns it up to 11.

vax425 11mo ago

I know! It took most of this summer to get my tide clock to predict accurately, using NOAA harmonic constituents data crammed into an Arduino, a GPS module, and published formulas. Take a look: https://digitalhorology.etsy.com/listing/4345582508 https://digitalhorology.etsy.com/listing/4345582508

teleforce 11mo ago

Reading most of the technology articles would have you to believe that dark ages really existed and for more than thousands years, i.e from Greece to Renaissance time there is no marine technology advancement between them. The truth of the matter is that the Arabic and muslim are the master of the sea during this so called "dark ages" time, and many advancement has been made from navigation gear of the Arabic astrolobe to the Idrisi map. In tide prediction Al-Kindi for example, has notable work on tides in his seminal book Treatise on the Efficient Cause of the Flow and Ebb back in 9th CE [1],[2]. [1]al-Kindi: https://en.wikipedia.org/wiki/Al-Kindi https://en.wikipedia.org/wiki/Al-Kindi [2] Al-Kindi: https://muslimheritage.com/al-kindi/ https://muslimheritage.com/al-kindi/

eesmith 11mo ago
From [1] > In a treatise entitled as Risala fi l-Illa al-Failali l-Madd wa l-Fazr (Treatise on the Efficient Cause of the Flow and Ebb), al-Kindi presents a theory on tides which "depends on the changes which take place in bodies owing to the rise and fall of temperature."
- teleforce 11mo ago
  Thanks for pointing that out but there's must some mistakes on the website. Al-Kindi contribution is on the experiment in showing that tides are caused by the expansion of water due to heat but of course later people know that it mainly due to gravity. Other well known Arabic and muslim reseachers in the middle ages working on ocean tides are Abu Ma'shar al-Balkhi (Albumasar), Al-Biruni and Nur ad-Din al-Bitruji (Alpetragius). Albumasar in his seminal book on tides was the first hypothesized the lunar correlation [1]. He's arguably the most important figure in the history of tidal theory between the ancient Greeks and Renaissance. His famous work namely The Great Introduction to Astrology (Kitab al-Madkhal al-Kabir) was translated into Latin in the 12th century and became the standard reference for European scholars (like Roger Bacon and Albert the Great) when they tried to understand tidal physics. Al-Biruni was a polymath who had direct experience with the strong tides of the Indian Ocean specifically at the port of Somnath in Gujarat, India. Of the 146 books written by him, 95 are devoted to astronomy, mathematics, and related subjects like mathematical geography [2]. In his encyclopedic work Indica (Kitab al-Hind), he discussed how the moon influences "moist substances". He dismissed the common myth in the region that viewed tides as the breathing of the earth or sea monsters. He firmly established the moon as the physical cause of the tidal cycle. This observation was using data gathered from sailors and his own measurements of the shoreline. Al-Bitruji was the very first astronomer who proposed an alternative to Ptolemy's model of the universe long before (more than 300 years) Galileo, by avoiding both epicycles and eccentrics mechanism [3]. According to him, the movement of the celestial spheres created a physical dragging force that stirred the waters of the earth, but his theory is less accurate than Albumasar's. Ocean tides was a significant area of study for Arab and Muslim reseachers during the middle ages (Islamic Golden Age), had extensive access to the Persian Gulf, the Red Sea, and the Indian Ocean, where tides are far more dramatic. The Greeks and Romans however, had a very limited exposure to ocean tides since they mostly observing the tide-less Mediterranean sea. [1] Abu Ma'shar al-Balkhi: https://en.wikipedia.org/wiki/Abu_Ma%27shar_al-Balkhi https://en.wikipedia.org/wiki/Abu_Ma%27shar_al-Balkhi [2] Al-Biruni: https://en.wikipedia.org/wiki/Al-Biruni https://en.wikipedia.org/wiki/Al-Biruni [3] Nur ad-Din al-Bitruji: https://en.wikipedia.org/wiki/Nur_ad-Din_al-Bitruji https://en.wikipedia.org/wiki/Nur_ad-Din_al-Bitruji

ljgfxxxxxth 11mo ago

All of these explanations are talking about “pulling” from gravity. What they should really be saying is that spacetime is being affected as the moon orbits.