Submitted 2 days ago by xkcdbot@lemmy.world [bot] to xkcd@lemmy.world
https://imgs.xkcd.com/comics/sea_level.png
Title text:
They’re up there with coral islands, lightning, and caterpillars turning into butterflies.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: xkcd.com/3135/
I remember never believing my parents when they explained it to me as a kid. Clouds being caused by cigarette smoke was reasonable but the moon pulling out the ocean seemed too outrageous.
Does the moon decrease the air pressure enough for that to matter?
Tides in the Bay of Fundy, Canada are 16 metres (50 feet).
See, that’s the part that confuses the hell outta me. How can water be higher in one spot than others just due to the Moon’s gravity? Yeah it’s the geography of the area, got it. But still, how?
Ever seen a ferrofluid, which follows the shape of magnetic fields? Same thing, but with gravity.
Of course, that only accounts for a fraction of those 16 meters… but there’s a lot of ocean water. Get it moving (because the Moon and the Sun move, and the Earth rotates under them, and there’s a whole lot of ocean currents on top of that, due to differences in water temperatures and salinity, and coriolis forces, and whatnot) and it builds up a lot of inertia.
Push it into geography that keeps narrowing and narrowing like a funnel, and the only place it can go is in, and up.
Water gets in there, wants to get out, but there’s a whole damn ocean pushing it in, so it has no option but to keep accumulating into the funnel.
Also, having the geography look a bit like a Tesla valve that’ll easily let water in but not so easily let it out probably doesn’t help either; place’s bound to get close to overflowing, before it can empty itself out.
Been trying to learn about the tides around here so I can tell what I’m seeing on the water. Imagine my joy when I found a Casio, which I collect, with tide and moon phase indicators!
And that’s when I learned the Gulf Coast is strange, has diurnal tides (twice a day) the watch can’t predict. Took me an hour and a half to figure out it would never function. The moon phase works!
Huh. TIL that there are three common types of tidal cycles and which one you get depends on geography, location, ocean currents. https://beltoforion.de/en/tides/tidal_cycles.php
Thanks. I didn’t know either that there are places, where the sea level does not rise and fall twice a day.
Me, too, TIL!
the Gulf Coast is strange, has diurnal tides (twice a day)
Diurnal tides are once a day (semidiurnal is twice a day). By the Gulf Coast, I guess you must mean the Gulf of Mexico. I’m living on the other side of the world in the other diurnal region, so I assume our tides are synchronised!
Gulf of America, you extreme left Antifa socialist!!1!one
No idea how I got that backwards. I even looked it up before posting!
Diurnal bros! Theres’s dozens of us!
Tidal prediction requires a harmonic analysis of observed tides, and its location specific. Not sure how a watch is supposed to do that other than holding a database of tidal coefficients.
This video contains a lot of interesting history of tidal analysis and prediction:
There are adjustments you can make on the watch. Requires tables and whatnot. That’s why it took me so long to figure out it wouldn’t work!
Tides go in, tides go out, you can’t explain that.
Casio can’t!
Now if you want strange tides look at Southampton. Not very big tides given its in the middle of the channel but the graph is an interesting one to look at.
Everyone was taught the tides look like two giant water bulges going around the earth in line with the moon.
That representation is oversimplified and false.
This is how the tides look like at a global level. It’s messed up.
Ok, that clarifies things so much better for me. Thank you.
In the Bay of Fundy, Canada we have the highest tides in the world (53 feet high). It’s enough to make some of the tributary rivers flow backward with the rising tide. I’ve seen it my whole life but it still amazes me to see a harbour completely empty of water with boats sitting on the bottom waiting for the tide to come back in.
"Tide comes in, time goes out - can't explain that!"
That’s some next level transformation, tide becomes time.
Soon scientists will discover dark tides and dark time, this could explain how tides go out and time seems to slow down or go backwards /s
Maybe one day dark light will be discovered which would help explain shadows and darkness at night or dark places /s
Imagine being out exploring new islands, not realizing its low tide. You setup camp for the night on an island that’s relatively flat and close to current sea-level. Then while you’re sleeping the tide comes in and washes your whole camp out to sea…
Come to the beach here in Bordeaux (well, on the coast) and see tourists set up their stuff at low ebb but forgetting they have to watch out for the flood.
There’s an island near me that has a pedestrian causeway at low tide. There are huge signs warning to check tide times or get cut off, but still people don’t get it.
if you are exploring islands you probably have a solid idea of how tides work.
You probably should, but that doesn’t mean you do. It’s not like anyone makes you take a quiz to go wander around outside.
Plenty of people get themselves into trouble all the time exploring places/things they know nothing about.
i lived near the beach for a while and, uh, i have seen tourists do the stupid. i posit they count.
“Their moon is tidally locked” is an absolutely metal thing to say about a planet.
I wonder if anyone has ever done the math on how much (in L or kg) water is moved by the moon each day. It’s got to be something absurd.
Just wanted to mention I see your pfp on every post and you always have nice takes or funny comments.
Thank you for keeping lemmy alive and making like 4% of the total posts. Seeing you post up my day.
No(Optional :3) homo.
Let’s hope Lemmy grows big enough that I can just be part of the crowd.
I have to assume it’s about one moon’s worth, divided by the distance squared.
That would be its total pull, not just the water.
We probably can estimate the amount of water that’s at a different level from what a moonless Earth would.
We could also say that technically all water is moved somewhat, because gravity is like that.
I think lightning would be crazy to anyone who never experienced a planet with it. Like, “WTF, sometimes your sky does what?”
FlatEarthersSayWhat
They'll just say the moon pulls the water around as it circles above the flat disc or something idk
But the moon alone doesn’t orbit at the same rate as the tides
“The earth tilts when the moon hits far end of earth during moonset and that’s why there is low tide. A high tide happens during moonrise when the moon drags it up slightly.”
Thats just the tilting from where the elephants shrug
I live in an area with sea but almost no tide (although wind direction can have a pretty big effect on water level) and I have always felt that tides are weird man.
Yeah I grew up inland and tides are weird
Nah, that’s just Poseidon having a bad mood today. Just have to sacrifice your first child to make it stop for 10 years.
And when Mercury is in retrograde, you can make an excuse for anything being kind of shitty or off.
There better not be mercury in my Gatorade!
No, no, no; We’re just giving Mercury a retro-grade.
I’m thinking maybe a C to C+ at best. I mean it’s kinda ‘retro’, but that’s definitely not the first description that comes to mind.
Just scoop it off the top, jeez.
woah XKCD is still making comics?
Well, tides on moons (eg around gassy supergiants :)) are fairly usual.
So perhaps it’s not as much as the tides being “sci-fi” (sci??) but the relative size of Earth’s Moon (it’s basically a binary planet situation where they orbit around each other).
So, the sheer size of our moon as seen from the planet’s surface is the rarity.
(Then again, on a moon around a supergiant the same experience could be had from one tiny beings pov.)
gassy supergiants
Ugh, there you go talking smack about my mamma again! Dammit, Evil Shrubbery!
Dense at the core, but what escapes is free for all the solar system to enjoy.
ohulancutash@feddit.uk 2 days ago
There are places in the solar system where the tide rips new mountains up every go around.
tacosanonymous@mander.xyz 2 days ago
That’s metal AF
Evil_Shrubbery@thelemmy.club 1 day ago
… some metal band (Dethklok?) recording their song/filming their vid/having the concert on such a moon - the guitar solo intensifies as the band is lifted upwards by a soaring mountain, epicly.
Evil_Shrubbery@thelemmy.club 1 day ago
True!
Going further - “tides” actually rip planets & starts fully apart (binary star systems, around black holes, yo mamma casually strolling through a galaxy).
Ugh@sh.itjust.works 1 day ago
Gasp! I’m telling my mamma you said that about her!!
(because it’s gonna make her giggle like an idiot, too, like it did to me!)
shalafi@lemmy.world 2 days ago
Io.
8baanknexer@lemmy.world 1 day ago
Where is that? Is that on one of the moons of Jupiter?
shalafi@lemmy.world 1 day ago
Io is the most volcanically active place in the solar system, by a long shot.