Neil deGrasse Tyson Explains the Lagrange Points 

Dr. Tyson... I emailed a question to the StarTalk email questionnaire and never got a reply. Just wondering, if I may ask your opinion on changing the units of time going forward in the future. I think my question was pertaining to a recent video you did on how time is relative and the response to Dr. James Gates video you did on "Proving Einstein right." Since planets can become distant planetary rock bodies, such as Pluto being recast from planet to rock body... can we change the unit of a "second" to the Banneker or give some extra homage to the unit measurement of time? Best Regards... -Siray

You were not incorrect Neil. You merely used a word that some people have yet to properly define is all. There remains a level of an eclipse of the sun by Earth at L2 where JWT is located. The center of the sun's disk always has Earth essentially directly in between it and JWT. And since we know that not every eclipse is total, a partial eclipse throughout the entire orbit is still a "permanent eclipse". Just not a full eclipse of which those who mentioned it were thinking. They were more incorrect than you were Neil. For they did not understand that not all eclipses are total eclipses.

But _why_ are L4 and L5 stable? Seems like the gravity from the two bodies (Earth & moon or whatever other pair) would be pulling things at those two spots inwards like a pair of elastic strings.

@@HopDavid like what?

@@HopDavid I think Neil has no issues admitting any mistakes he's made. In fact he pinned his mistake and explained his mistake: Pinned by StarTalk Neil deGrasse Tyson 1 month ago (edited) Hi Everybody, just noticed that around 10m28s into the video I say that Earth permanently eclipses the Sun at L2 point, keeping JWST in shadow. But that's not correct. Earth will eclipse the Sun at that location but not always where JWST meanders. (L2 is a big area in space.) JWST's built-in Sun shade is what will keep it shaded. Thanks to a bunch of folks in the comment thread for noticing that error. -Neil deGrasse Tyson.

He's Watson, only funny.

CHUCK IS THE MAN. NOBODY PLAYS THE COMEDIC TIMER BETTER. CHUCK IS ALSO LEARNING WORKING ALONGSIDE DR. TYSON, HE'S VERY SMART, VERY.

When i look at the top & see all the succesful people.. there is NO mexicans 😩I review weed products on my RU-vid channel .. tryna make it out💯..

I've seen Mr. Nice go from hardly understanding Dr. deGrass Tyson to keeping up even though he can still be impressed. I've been a fan for years. Comedy and intellect or not exclusive parts of our minds. They both have it all.

And he's the only one who can interrupt Neil...

Same bro

The bromance

French fan approved! Thanks for the kind words, glad you enjoyed :)

@Hollister David could you elaborate on these so called false histories?

@@thebeast5215 This David is most probably a flat earther or creationist believer, just by looking at his words and his comments on other vids and channels that he's following.

@@waynewynnx7976 He is bar NONE, one of the most uneducated trolls the internet has ever known. You will never find anything factual with anything he says. And absolutely never will any level of education make it through his intentionally think skull which despises objective truth at all cost. He will almost never leave his own comment and will mostly only ever defecate upon other's comments which are based upon undeniable fact. He is a stalker in a sense. If you make the mistake of responding directly to him, he will locate ANY AND ALL of your social media activity in direct effort to attempt to insult and harass with nonsensical ramblings no one capable of critical thought can make sense of. To be honest, I believe that he believes ONLY in opposition, nothing else. He is convinced it grants him a personality. Matters not the topic, he only ever opposes without logical defense of his chosen opposition. He has called airplanes "non-existent". Claimed there is "no oxygen within Earth's atmosphere". And that lizard alien people have taken our brains, but never his. All because he came across a factual post or comment stating otherwise and no other reason whatsoever. It is STRONGLY advised to block him on every social media channel. Sure, it can be fun to poke holes in his nonsense. But that fun is quickly replaced with sheer annoyance, for he NEVER stops once he gets going. If you ignore one of his ridiculous responses, he merely continues tagging while offering increasingly more ignorant responses. And as with ALL internet trolls, he becomes entirely silent when face to face. He ONLY does this when he can falsely believe that his keyboard keeps him protected.

@@HopDavid I do not use the information, just the humour.

@@HopDavid Please explain. What information is incorrect?

We're glad you enjoy it! Cheers to you, fellow educator.

Agreed

@@HopDavid Good points, but you're being pretty nit-picky. At L1 the acceleration due to gravity is EXTREMELY low, as is the centrifugal acceleration. So, when you say the Earth's pull is much stronger than the moon's, that is technically correct, but both "pulls" are but the slightest of fractions that one feels near the surface of either body. It's a very, very weak game of tug o' war. As for the JWST's orbit around L2, you're spot on. Indeed, the diameter of the orbit is about the same distance as L2 is from Earth; a fact that I think is lost on most folks. NASA intentionally put the satellite into this L2 orbit to improve it's ability to image in all directions.

Lol bro

it really is the best a man can get.

You are right Sir.

I think that his definition of L1 is also wrong. He says a 3:50 that L1 is where the gravity of Earth and Moon are equal (and in opposite direction so they cancel each others). This is an oversimplification because there is gravity at L1. It is defined as a point where Earth gravity is reduced by the Moon gravity thus allowing an orbit with the same period as the Moon orbit. For example, Earth-Moon L1 is at 85% of the Earth-Moon distance. The Moon gravity at L1 is 38% of Earth gravity and consequently the overall gravity is still 100-38 = 62% of Earth-only gravity (so not zero). If you plug 85% of the distance and 62% of the mass in the formula that gives the orbital period then they will cancel each others (e.g. 0.85^3 = 0.62) thus providing a orbit with the same period than the Moon.

He is also wrong when he says that the James Webb telescope was placed at L2 because at that location Earth permanently eclipses the Sun. That would only be true if JW was exactly at L2 but in fact it follows an orbit around L2 that is larger than the Earth-Moon orbit. I would not be surprised if JW was never going through the shadow of Earth. In fact, JW has solar panels so it probably requires sunlight to operate.

And Lagrange was italian, he was born in Turin

You're totally right of course, however I think that is the flavour of this channel. If you want something more substantial PBS Spacetime is the one

Yes Sir.

yeah otherwise there would be no reason for the solar panels or tennis court sized sun shield.

Thank you, I was looking for this comment

Came to the comments to say this, happy to see you’ve done my work for me. I expected better from you, Dr. Neil!

Yes! The main benefit is that JWST does not have to shield its eyes from 3 heat sources (sun, moon, earth) in different parts of the sky. They are all hidden behind the one “visor”, the sun shield.

Right, and my comment was deleted as soon as I pointed that out.

@@Izaguirre2002 I just made a similar comment. It could be that your comment was deleted by RU-vid, I've noticed that a comment is very likely to be deleted if you used copy/paste.

That's right! That was a mistake. The spacecraft is actually permanently in sunlight!

@@Gerard1971 I stand corrected, it had link to a NASA blog talking about the solar array deployment.

@@HopDavid Yes, it had a link to a nasa blog talking about the solar array deployment.

They both smoked a big fat j before recording.

So glad you enjoy!

@@HopDavidan object at Earth-Moon L1 feels the Earth's gravity, the Moon's gravity, AND a centrifugal force because the E-M L1 point is moving at the Moon's orbital velocity.

@@HopDavid fair point. Also why i have more respect for chuck. He knows where he stands on all this so he only goes for a reach when a joke is there

That’s an easy fix, make your own video explaining it your way🤷🏾‍♀️

@@katrinamichelle8373 100%

Whats the other half?

@@HopDavid Well, he oversimplified it AF that might be way

@@HopDavid ook

Why not both!

Awesome to hear that! Glad you could enjoy it.

@@HopDavid I was going to ask for a source, but looked it up myself, and it seems that the scope is not in Earth's shadow. Ty for the info.

Learning is fun!

@@StarTalk oooooo doctor, doctor! I just read a couple of articles that JWST orbits L2, instead of ‘sits at L2 permanently being eclipsed by the Sun’. Now I’m more intrigued as to ‘how’ the unstable legrangian points (1, 2, and 3) can have their own orbital paths? Much like the JWST has of L2? Or did I mess that question up?

Agreed. But don't forget that Chuck is the new host of Brain Games on Disney+!

@@StarTalk I had no idea I'll check it out thank you

Yes! Approved by a French fan. Thank you!

That's... not possible. You can't just "create" magnetic fields to protect entire planets. That's just science-fiction.

@@louisrobitaille5810 that’s true, i didnt formulate it very well. What I meant to say was the hypothesis about creating a magnetic field around mars to help it being terraformed, but it’s true sadly we don’t have the technology quite yet…

@@adrianwulff2608 We'll never have it... This will always be science fiction. The only way to create such a magnetic field would be to create a make a dynamo out of Mars' core. That's how all the massive magnetic fields in the universe work, e.g. the Earth's, the stars', and even dead stars remnants' like pulsars or more specifically magnetars. For funzies and reference, the Earth's magnetic field is measured in microteslas whereas an average magnetar is 10^15 teslas. A tesla is the unit of measurememt of the strength of a magnetic field. A microtesla is 10^-6 tesla.

As the moon's orbit is between the earth and sun, the earth and sun are both pulling on the moon in opposite directions. When the lunar orbit is furthest from the sun, then the sun and earth are working together to keep it balanced.

@@HopDavid Thanks! How bad does it affect stabilization at the L4 and L5 moon/earth points?

Well, yeah, "the three body problem" is ultimately chaotic. And so no system of three (or more) objects can ever be truly stable. Because, like, whatever object you place at a Lagrange point itself has mass - and therefore gravity - and it's now a three body system. So, now, adding this third object into the system - to create a Moon-Earth-Satellite system - you've got to consider the satellite's gravity on the Moon and the Earth. Yes, in practice, this is so infinitesimally small - as the satellite is tiny compared to the vast sizes of the Moon or the Earth - that we just fudge it and pretend like it's zero. But, technically, it's not exactly zero - just very, very, very, very small - and it is having this tiny minuscule effect. And that's where Chaos Theory kicks in, because no matter how tiny that non-zero difference is, it's accumulating over time. So, like, eventually, over very long celestial periods of time, it will add up to something significant. Gravity, as far as we know, has no limits on distance. But it attenuates according to the inverse square law: Twice the distance away then it's going to be four times weaker, three times the distance then 9 times weaker. Thank you, Mr. Newton for working that one out. So, really, every object in the universe is gravitationally affecting every other object in the universe. It's just that, over immense distances, that gravitational influence is so infinitesimally tiny, we fudge it and just treat it like it's zero. But, technically, it's not exactly zero. And this is where Chaos Theory comes in, because even though it's tiny, tiny, tiny in magnitude, it's accumulating up as time passes, and, eventually, after an insane amount of time, the butterfly's wings will cause a tornado on the other side of the galaxy. So, in that sense, nothing in the universe is truly stable. It's impossible. But, you know, in practice, we grossly simplify. Even though these things are technically non-zero, they're so damned close to zero that we just act like they are zero and ignore them. You can't practically take account of every single object in the whole universe when you're plotting a course for your satellite. And the point is that, in practice, you don't need to. The gravitational influence of Alpha Centauri - the nearest star to Earth - is so infinitesimally tiny, that we can safely just treat it as if it's zero (technically, it's not zero - gravity, as far as we know, extends forever - but it's so unbelievably close to it, we can totally get away with the simplification of treating it as if exactly zero). Every asteroid. Every particle of dust, even. Every single atom of hydrogen just floating out there by itself somewhere. They all have mass, and therefore have gravity. But when it's really tiny and really far away, then - inverse square law - it's so close to zero, we can treat it as if it were exactly zero. And, you know, just ignore it. There's a joke quote: "In theory, there's no difference between theory and practice. In practice, there is". And this is an example of that. In theory, everything with mass is exerting gravitational influence on everything else with mass - every object in the whole universe is pulling on every other object in the entire universe - but that's an impossible calculation to make. But, in practice, nearly everything - except for the big and close stuff - has negligible impact on your calculations, so you can throw away most of it, pretending like it's exactly zero (because it's so damned close to zero, it's really not going to change the conclusions of your calculations in any way). So, Lagrange meets Chaos Theory, and the real truth is that no location anywhere in the universe is truly 100% "stable". But, ah, it's close enough. For all practical purposes, it's so close to "stable" that, ah, we can treat it like it is. Or, more precisely, it's "mostly stable" and then we can give the satellite a thruster and some fuel... and we can then "correct" any tiny drifting away from perfectly stable. It's always a simplification, in the sense that we treat it like a "two body problem" or a "three body problem" and so forth, for our calculations. But, in reality, every object gravitationally influences every other object in the whole universe, so it's always a "every-object-in-the-universe body problem" in truth. But you can't practically deal with that. And, in practice, you don't need to. Just focus on the big and close objects, which have the lion's share of the gravitational influence, and act like everything else is zero. Alpha Centauri is having a gravitational influence on the Moon. But it's so ridiculously infinitesimally tiny, it's effectively meaningless and we just ignore it. It's close enough to the right answer. It's close enough to "stable" to be practically useful (and a retro-thruster can just fix any "drift" that occurs over time). There's the mathematical theory we work out in our calculations. But then there's also just being practical, in an engineering sense, of saying, ah, that's close enough. it's mostly right and who cares about our calculations being 10 atom widths out? It's good enough to be useful, and we can "correct" for it with retro-rockets. Basically, as the shepherd says to his sheep dog: "that'll do, boy. That'll do". In theory, all these calculations could go to infinite decimal places of precision. But, in practice, you can't pragmatically work to those levels of precision - we can't even measure things that precisely - and there's an "error range" where it just doesn't matter. If your satellite is 3 microns off where it should be, this really won't make any useful difference to anything. It'll do. It's close enough. We can work with this. It's always a simplification, but it's more than good enough, practically speaking. Like, maybe this satellite would, over a billion years, drift away from the Lagrange point. But, like, the satellite is not going to still be working in a billion years. As long as it's good enough for the decade or so that we're actually actively using it, then, ah, "that'll do, boy". If you like, it's the difference between a theoretical mathematician and an engineer. For the engineer, it's close enough. I can work with that. It'll do, for the purposes we have in mind. It doesn't have to be infinitely precise, just close enough that we can actually get the job done. So, yeah, in theory, every single object in the whole universe is contributing to the calculation. Yes, all of them. Everything with any mass at all. Even a single lone atom floating out there in the vast oceans of nothingness between galaxies. Every last bit of it. Anything - and everything - with mass has gravity, and gravity, as far as we know, extends forever. BUT, at the same time, gravity falls off by the inverse square law. So that's one over the square of the distance. Multiplied by its mass, so very tiny things contribute almost nothing. You get the picture - the gravitational influence of anything tiny or really far away falls off in an exponential way to effectively "so close to nothing, we might as well treat it as nothing" in very short order. I have mass. Therefore, I have gravity. But, like, my contribution to the Sun-Moon-Earth system? it's not worth considering. But, technically speaking, it is there. It's just so uselessly tiny, we can safely ignore it. So, in all of this talk of Lagrange points, you can introduce "but what about the Sun?" or "but what about the planet Venus? The planet Jupiter? The Oort Cloud? The Magical teapot that floats between Earth and Mars?"... and, technically speaking, they're all having some gravitational influence. As I say, every object in the whole universe is affecting every other object in the universe. You can literally extend this logic to encompass absolutely everything. But there's no point. Only the big and close things really make any serious difference to the conclusion, and you can safely disregard everything else and be so close to the correct answer that, in practice, it doesn't matter. If you like, every calculation we make has an "error range" on it. But if that "error range" is only a few microns or even millimetres then, in practice, who cares? As long as it's within tolerances, it's good enough. It'll do. We can practically work with that.