A physics question, 'cause I'm weak in the noggin

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A physics question, 'cause I'm weak in the noggin

Postby Crescent Pulsar S » Sat Sep 03, 2016 7:43 pm

Okay, let's say that the solar system in the fictional setting is as it is in reality. Now, an Earth-sized planet appears roughly the same distance away from the sun, on the opposite side from the Earth. By the time twelve hours has passed since its arrival, the sun has been moved to the other side of the new planet, so the new planet is now between it and the Earth. The sun will continue to revolve around the new planet, making one revolution every twenty-four hours.

So, yeah... There are a couple of layers and perspectives of information that I'm hoping to learn about this scenario. Like, when would the abnormal movement be noticed? How would it look from Earth? (For simplicity's sake, from the northern hemisphere during the Summer.) What would be the first noticeable and tangible effects solely on the Earth, possibly including long-term projections? Would it disturb the Earth's orbit; and -- if so -- in what way? And then there's the affect on the solar system in general, whether Mars, Venus and/or Mercury will be hit and destroyed by the sun, or get close enough for the same results, if the same could happen to the Earth, or if their orbits will simply end up changing instead of being set on a course that's outside of the solar system.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Ellen Kuhfeld » Sat Sep 03, 2016 8:34 pm

You are speaking of a Ptolemaic solar system; the real thing is Copernican.

What you have done is put another Earth in the L3 Lagrangian point. Since it is opposite the sun, we won't see it from Earth - spaceprobes might, if they look. The major factor here is that solar gravity appears to increase slightly (by adding the gravity of the second Earth). Thus both Earths will move very slightly faster in their orbits. But in a world that keeps track of leap seconds, it wouldn't take long for astronomers to notice something off.

Expect a period of confusion while physicists check to see if the gravitational constant has proven - inconstant. But effects on the solar system will be small. It is the Sun, Jupiter, and quite a few bits of debris going around in ellipses. Some of the debris is larger than others, of course.

If you really want to set the cat among the pigeons, try a second Jupiter.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Spica75 » Sat Sep 03, 2016 10:23 pm

Okay, let's say that the solar system in the fictional setting is as it is in reality.


With that statement, you make the rest impossible as what you describe does not conform to reality.

By the time twelve hours has passed since its arrival, the sun has been moved to the other side of the new planet


Earth circles the sun in 12 months, not the sun circling earth in 12 hours.

For the new planet to manage that little stunt, it would have to be in spitting distance of the sun. Mercury is a very hot place(anywhere of it pointing towards the sun(420C), while the other side tends to be between -90C to -170C) yet travels around the sun in 88 DAYS. The new planet being that close would mean that it is constantly burned very "crispy" on the facing side.

The sun will continue to revolve around the new planet, making one revolution every twenty-four hours.


Impossible. A planet the size of earth could never come close to generating the gravity well strength needed to make the sun revolve around it.


Now, an Earth-sized planet appears roughly the same distance away from the sun, on the opposite side from the Earth.


If this is what you actually meant, including it having an orbit like that of Earth, then Ellen´s reply is how it goes.

To have the sun orbit around the new planet, you must give the planet at minimum a similar or greater mass than the sun. To give it such an extremely fast orbit as to get your 24 hour orbit, the mass needed goes from extreme to beyond ridiculous. I haven´t tried to calculate anything, but from what i recall, i don´t think even a supermassive black hole would be enough for the sun to suddenly run off to the side that quickly.


I think a better question would be, what generated your question in the first place?
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Re: A physics question, 'cause I'm weak in the noggin

Postby Slab Bulkhead » Sat Sep 03, 2016 11:37 pm

Earth 2 would wobble slightly relative to an observer on earth because the earth is not in a perfectly circular orbit. Probes like SOHO that are looking at the sun from earth orbit would see it, the STEREO probes which are on the other side of the sun from the earth would be able to detect it indirectly because of gravitational perturbations from Earth 2.

But more importantly, the Earth-Sun L3 point you're talking about is not a stable position, and t would only be a matter of time before any celestial body that was positioned there would be nudged out of orbit.

EDIT: L1 (the point between the sun and the earth), L2 (a point where the earth is between you and sun), and L3 (a point on the exact opposite side of the earth from the sun) are all inherently unstable, and trying to put anything there is like trying to balance a marble on top of a basketball. It requires CONSTANT adjustment to keep it in that position.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Knight of L-sama » Sun Sep 04, 2016 3:15 am

Slab Bulkhead wrote:EDIT: L1 (the point between the sun and the earth), L2 (a point where the earth is between you and sun), and L3 (a point on the exact opposite side of the earth from the sun) are all inherently unstable, and trying to put anything there is like trying to balance a marble on top of a basketball. It requires CONSTANT adjustment to keep it in that position.


That's not to mention that there are mass constraints for a Lagrangian orbit, even the more stable L4 and L5 orbits. A ratio of 24.5 if I remember correctly. Something the approximate size of the Earth in any of the Lagrangian points are going to destabilize not only their orbits but Earth's. As for how long it would take to notice... probably days to weeks for the really sensitive equipment, months to years before the maco-effects start kicking in.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Ellen Kuhfeld » Sun Sep 04, 2016 7:35 am

Knight of L-sama wrote:That's not to mention that there are mass constraints for a Lagrangian orbit, even the more stable L4 and L5 orbits. A ratio of 24.5 if I remember correctly. Something the approximate size of the Earth in any of the Lagrangian points are going to destabilize not only their orbits but Earth's. As for how long it would take to notice... probably days to weeks for the really sensitive equipment, months to years before the maco-effects start kicking in.

Perhaps I should not have said "Lagrangian". As you point out, such a situation must have (Big Mass), (Not as big mass), and (Particle of tiny mass relative to the first two). The situation in this question is (Big Mass) and (Two particles of small mass relative to the first). The effect earth-1 has on earth-2 is matched by the effect earth-2 has on earth-1. If it were a three-body problem, and the rest of the Solar System weren't there, an 'L3' circular orbit would be quasi-stable -- much more so than a traditional L3.

This assumes, of course, a circular orbit. Earth has a somewhat-elliptical orbit. If we started going there, you'd need a supercomputer to answer the question. I don't think you want to get a supercomputer involved.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Crescent Pulsar S » Sun Sep 04, 2016 6:15 pm

Thanks for the help so far, guys/gals.

And I can't believe (although I actually can) that I forgot about SOHO. That would be really helpful for the beginning of the story.

Spica75 wrote:With that statement, you make the rest impossible as what you describe does not conform to reality.

You're looking at it the wrong way and assuming the wrong things. When I said what you quoted, it was merely to establish that the solar system in general looked and functioned as it does in reality. Whether the change that occurs after that is possible or not is inconsequential, which is why I asked for its affects rather than addressing what you did first.

Since you wondered about it, and I left it out because it wasn't relevant to what I was asking, what's introduced to the solar system is My Little Pony: Friendship is Magic. :P
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Re: A physics question, 'cause I'm weak in the noggin

Postby Spica75 » Sun Sep 04, 2016 7:09 pm

Since you wondered about it, and I left it out because it wasn't relevant to what I was asking, what's introduced to the solar system is My Little Pony: Friendship is Magic.


Then simply put it in orbit around the sun, same orbit as Earth but other side of the sun. That way you get a reasonably stable orbit and don´t have to explain away effects that simply could not happen with an extremely massive force added into the mix.

You're looking at it the wrong way and assuming the wrong things. When I said what you quoted, it was merely to establish that the solar system in general looked and functioned as it does in reality. Whether the change that occurs after that is possible or not is inconsequential, which is why I asked for its affects rather than addressing what you did first.


I wasn´t assuming anything, i went exactly with what you said.

Problem was the statement of having the sun suddenly orbit the new planet in a 24 hour orbit. Just not going to happen.
At 1 AU distance, the Earth has an orbit time of 365 days, at 0.46 AU, Mercury has an orbit time of 88 days. To reach 24 hours you would need to be in what is effectively called geostationary orbit, which is just under 36000km, while an AU is 150000000km.

If you DO put the new planet as stated, and then FORCE the sun to dash off into a 24 hour orbit by effectively using insane amounts of energy to control the sun, to suddenly move the sun at EXTREME speed to make it move close enough to the new planet that a 24 hour orbit is even remotely possible, you´re going to burn up the new planet, nothing on it will survive, you´re also going to drop the average temperature on earth drastically, almost literally overnight when the sun flies off to twice the distance it was the day before(expect earth average temperature to drop from 15C to maybe -55C or something, effectively ending the vast majority of life on earth in the near future), and depending on where other planets are in their orbits, Mercury and Venus(Mars is possible but not as likely) could end up doing "playing pool with planets", or simply "go rogue"(ie disconnect from the gravity well of the solar system and start taking a route of their own)...

Basically, doing EXACTLY what you said, then you kill everything on both Earth and new planet. It is also questionable if the new planet will even survive coming so close to the sun. Actually unless i misrecall, the new planet will end up inside the sun as the sun has a radius counted in the hundreds of thousands of km.


After checking it up, the stable orbit around the SUN, 24 hour orbit, would be 0.019 AU. The sun takes up most of the visible sky, not than anyone is going to be able to see it, being burned crispy and all. The sun is just ~4 times its own radius away from the planet.
If you make the sun orbit the planet, due to the smaller gravity well, that shrinks down to 0.002 AU. Planet just got eaten by the sun.
Sun radius, ~695700km, 0.0046 AU.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Crescent Pulsar S » Mon Sep 05, 2016 6:48 am

Spica75 wrote:Then simply put it in orbit around the sun, same orbit as Earth but other side of the sun. That way you get a reasonably stable orbit and don´t have to explain away effects that simply could not happen with an extremely massive force added into the mix.

I probably could have made it more clear, but that's where I said the new planet is.

I wasn´t assuming anything, i went exactly with what you said.

Problem was the statement of having the sun suddenly orbit the new planet in a 24 hour orbit. Just not going to happen.
At 1 AU distance, the Earth has an orbit time of 365 days, at 0.46 AU, Mercury has an orbit time of 88 days. To reach 24 hours you would need to be in what is effectively called geostationary orbit, which is just under 36000km, while an AU is 150000000km.

If you DO put the new planet as stated, and then FORCE the sun to dash off into a 24 hour orbit by effectively using insane amounts of energy to control the sun, to suddenly move the sun at EXTREME speed to make it move close enough to the new planet that a 24 hour orbit is even remotely possible, you´re going to burn up the new planet, nothing on it will survive, you´re also going to drop the average temperature on earth drastically, almost literally overnight when the sun flies off to twice the distance it was the day before(expect earth average temperature to drop from 15C to maybe -55C or something, effectively ending the vast majority of life on earth in the near future), and depending on where other planets are in their orbits, Mercury and Venus(Mars is possible but not as likely) could end up doing "playing pool with planets", or simply "go rogue"(ie disconnect from the gravity well of the solar system and start taking a route of their own)...

Basically, doing EXACTLY what you said, then you kill everything on both Earth and new planet. It is also questionable if the new planet will even survive coming so close to the sun. Actually unless i misrecall, the new planet will end up inside the sun as the sun has a radius counted in the hundreds of thousands of km.


After checking it up, the stable orbit around the SUN, 24 hour orbit, would be 0.019 AU. The sun takes up most of the visible sky, not than anyone is going to be able to see it, being burned crispy and all. The sun is just ~4 times its own radius away from the planet.
If you make the sun orbit the planet, due to the smaller gravity well, that shrinks down to 0.002 AU. Planet just got eaten by the sun.
Sun radius, ~695700km, 0.0046 AU.

Why can't sunbutt (AKA Celestia) move the sun as she usually does? (I mean, aside from the whole thing about magic not existing prior to this event.)

I appreciate hearing about the effects on the Earth, which I'm glad you got around to despite what seems to be a misunderstanding. Although I'm guessing that the conditions on Earth would be worse, since the sun would be three times the distance from the Earth at its farthest.

As an aside, the world from MLP: FIM doesn't have to appear at a similar distance from the sun as the Earth is. I also wouldn't mind exploring what would happen if it appeared close enough to the Earth to be a satellite or become a part of a binary system.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Neko- » Mon Sep 05, 2016 8:38 am

If the planet would show up in our solar system, I'm unsure what would happen to the orbits of Mars, Venus and possibly Mercury (to the latter may not be affected at all due to it's proximity to the suns gravitywell).

If the planet would have a different mass than Earth (smaller or bigger) it might well trigger irregular planetary orbits.
Same goes if the planet is moving at a slower or faster pace than Earth (we perceive a year to be 365,25 days - Who is to say the ponies don't work with 400 days (100 days per hoof/season)?
Then we get to the rotation of the planet. In other words, the length of a day. While we work with a 24 hr clock (and a correction every now and then), the ponies could work on a 20 hr or 40 hr clock.

While the moon of the planet may not have a profound impact, it does add to the gravity well of the planet in the grand scheme of things, and the show does show the moon to be much bigger (or atleast closer) than our own moon. But the length of day and night are also going to be making an impact here, dictating how long the moon will be in a certain area relative to the planet. And thus it's gravitational pull on other objects in the solar system.

All these factors mean that if we assume the new planet to have the same mass, velocity and 'rotational speed' as Earth, we may find it manages to achive a stable orbit directly opposite from Earth. Hell, magic may negate any weight/gravity issues all together, tho that's a bit of a far fetched assumption). If the planet is slightly off however, there is a chance this may start to impact oribital patterns in the long run.

But we'll assume a stable orbit for now. As soon as magic is going to be dragged into this, all bets are off.

While Celestia may not have sufficient power to move the sun, but instead manages to speed up or slow down the orbit of the planet according to their own clock (which MAY even be how it works in the show, since a planet is usually smaller and thus easier to move, which would still allow for irregular solar movements from the planets surface), the end result will potentially be Earth and the planet colliding. While the planet may be controlled through magic, the Earth will receive a gravitational pull from the back or front, which will either speed-up or slow-down the earths rotational orbit. We don't have the benefit of something that may alter our speed around the sun. And this may cause the Earth to assume a larger or smaller orbit around the sun. The movement of the planet may also upset the orbits of Venus and Mars to a degree.

If we proceed to add in the planets moon, with it's own gravity well, and the movements it may make, the predictability of the system takes an even further nosedive.

If you choose to have the MLP planet appear opposite from Earth, depending on where you want to take the story, you'd be best off accepting a lot of assumptions as truth. Either that, or go for a disaster-style fic, in which the planet (and Earth) may well be destroyed (collision, sun gravity well, debris from other planets colliding) as part of some minor nudges a certain pair of alicorns made. *My name is Celestia... Destroyer of Worlds*

You might have some fun with this: https://phet.colorado.edu/sims/my-solar ... em_en.html
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Re: A physics question, 'cause I'm weak in the noggin

Postby Spica75 » Mon Sep 05, 2016 9:33 am

Why can't sunbutt (AKA Celestia) move the sun as she usually does? (I mean, aside from the whole thing about magic not existing prior to this event.)


Because regardless HOW it´s done, it will take ridiculous amounts of energy to do it?

Although I'm guessing that the conditions on Earth would be worse, since the sun would be three times the distance from the Earth at its farthest.


Now, this suggests you expect the sun to be able to orbit a planet at the distance the Earth currently orbits the sun rather than having a natural orbit.

THIS, would entail accelerating the sun to 365 times the orbital speed of earth, and because there´s no gravity well keeping it in that orbit, constantly maintaining that control. So, Earth normal orbital speed is just under 30km/s, you are instead going to need to need the sun moving at 10800km/s. Maintaining that constantly will require the initial acceleration required for it to happen, to be applied continuously, without slightest pause, ever.

If you have Celestia have that kind of powerlevel, why bother moving a star? She can just say "there be light and heat" and be done with it and then take the rest of the day(or year, or century) off. That would take a tiny fraction of the energy she´s spending on controlling the star.
And seriously, why bother MOVING a star when letting the planet rotate on its own instead takes a barely noticeable amount of energy in comparison? Not to mention how it only needs to be done once, instead of being maintained constantly.

I have no problem with the "a wizard did it/it´s magic" explanation, but the power level involved in the above probably makes Celestia the most powerful magic user ever seen in fiction. Possibly by orders of magnitude. It´s an automatic God Mode "I win" button. There´s simply nothing with the level of power to stop her from doing whatever she wants.


And if you do this "implant", you will effectively destroy the rest of the solar system in short time. With the primary gravity well moving around at high speed far outside of it´s normal position in a relatively wide orbit and completely ignoring physics, it´s only a matter of time before the rest of the planets are sent off into deep space.

Longterm, that also means that Jupiter´s effect as a meteor shield is gone.

There´s also a chance that it could disrupt the local galaxy as well(and i´m not even sure how small or big that chance would be). Having a star start moving that fast in such a way is essentially like introducing a vibration in a nonsolid material. It´s a tiny thing on a galactic scale, but constantly introducing so much extra energy, well it´s unlikely to just go completely unnoticed.

So, you might just have made MLP:FIM the evil galaxydestroying alien invaders... :mrgreen:
And you HAVE made them the evil STAR system destroying alien invaders. :P
Oops?

I also wouldn't mind exploring what would happen if it appeared close enough to the Earth to be a satellite or become a part of a binary system.


As long as you include the "move and control a star at insane speeds", that´s not going to work. Earth would very soon be slingshot away. It comes down to one simple part of reality, the sun has a mass 333000 times greater than Earth, and adding a second, similar planet nearby doesn´t make any real difference to the force the sun is going to enact irregularly on the Earth due to the extreme speed of orbit.
The MUCH bigger gravity well always wins.

And in the meantime, with the Earth already spinning, you´re going to make day and night there roughly halftime until the Earth goes walkabout(either that or a constant day/night division due to being locked with the same spin as the sun orbits).
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Re: A physics question, 'cause I'm weak in the noggin

Postby Spica75 » Mon Sep 05, 2016 9:54 am



:mrgreen:

I tried running a few simulations, and while that is very oversimplified, before the time reaches 600, there´s usually either an impact or one of 2 planets gets slingshot away or ends up orbiting so far from the "sun" too much of the time that i wouldn´t want to live there.

I wonder if there´s anything like that, that would allow the nonnatural orbit required by CPS to be included? Probably not i expect.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Neko- » Mon Sep 05, 2016 10:16 am

All models are based on the standard based planetary orbits...

CPS wants to include an 'orbit' where the massive gravity wel orbits a small planet, at which point the rest of the solar system is going to follow that massive gravity well.

The fact that this alone flies straight in the face of all known logic and standards known, makes me pretty sure it's not something anyone ever conceived for a modeling of what would happen :)
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Re: A physics question, 'cause I'm weak in the noggin

Postby Ellen Kuhfeld » Mon Sep 05, 2016 12:28 pm

One final comment: you have not asked "A physics question," CP. You have asked a magic question. Expecting the rest of the Solar System to compensate for the magic by way of physics Does Not Compute.

Do what you want. "It's magic. An Alicorn did it." But stop asking physics and astronomy to hold hands and smile about it. They're as confused as you are.
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Re: A physics question, 'cause I'm weak in the noggin

Postby Spica75 » Mon Sep 05, 2016 2:02 pm

Neko- wrote:All models are based on the standard based planetary orbits...

CPS wants to include an 'orbit' where the massive gravity wel orbits a small planet, at which point the rest of the solar system is going to follow that massive gravity well.

The fact that this alone flies straight in the face of all known logic and standards known, makes me pretty sure it's not something anyone ever conceived for a modeling of what would happen :)


Nah, it will be travelling waaayy too fast to actually be a stable gravity well like that. Think about it, in the time the earth WOULD have travelled around the sun once, instead, the sun has travelled around the new planet, 365 times, shifting from a distance of 1 AU to 3 AU on a daily basis. And twice per day, the sun would cross the orbit of the new planet(IF it does have an orbit at all, otherwise it´s just a matter of waiting for earth to either crash into it, or into the sun(or the sun crashing into earth during its hyperspeed orbiting)), and present gravitational pull far to the side. Not healthy for the orbit of earth.

Venus and Mercury are going to get slingshot very quickly as they are no longer orbiting anything AND will have "close encounters" of the very wrong sort once a day the moment they are close to the new planet.


The only way for the other planets to follow, is for someone to forcibly pull them into orbit around the new planet, which the sun now orbits instead. And i very much doubt even that "solution" will result in any kind of stable system. In fact, i´m almost certain that it will result in a drastically unstable system, with all planets going rogue due to the primary gravity well not being the center, as well as the extreme speed it is moving around with.
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