I Know This Isn't Realistic by Haken

GENERAL DISCUSSIONS

I Know This Isn't Realistic

POSTED BY: HAKEN
UPDATED: Friday, September 27, 2002 19:47
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VIEWED: 3601
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Thursday, September 26, 2002 1:53 PM

HAKEN

Likes to mess with stuffs.

Take a look at this from the 'The Train Job'

I'm guessing the largest one in the background is a planet. The other two are moons. One seems to be terraformed. The one Malcolm is on must be a moon as well because there's just no way for two planets to be that close together.

But how the heck do you explain all these terrestial objects being so close together in distance without gravity ripping everything apart? There's just no way.

A bit overzealous with the cut and paste I think.

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Thursday, September 26, 2002 2:00 PM

HOBBES

Great looking shot though.

The answer is that the moon they're on has a strange chemical that magnifies images that are outside the atmosphere :)

-------------------------------------------------
May the road rise to meet you.
May the wind be always at your back.
May you be in heaven an hour before
The Devil knows you’re dead.

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Thursday, September 26, 2002 2:23 PM

LIVINGIMPAIRED

________________

"I love to see a young girl go out and grab the world by the lapels. Life’s a bitch. You’ve got to go out and kick ass." —Maya Angelou

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Thursday, September 26, 2002 3:08 PM

ZICSOFT

How can you form any judgment about how big these objects are if you don't know how far they are? And vice versa? Look up in the sky some time when both the sun and the moon are visible. Their apparent size is very close (a coincidence that has always bothered me). Yet the sun is 400 times bigger than the moon! Being 400 times farther away cancels this out.

In any case, one's perception of the "size" of the moon is grossly distorted. A full moon looks like it takes up a huge chunk of sky, especially when it's near the horizon:

http://facstaff.uww.edu/mccreadd/

But look how tiny the moon actually is against an objective backdrop:

http://www.freemars.org/jeff/Luna2b.htm

I don't have the math to say this with authority, but try this: Mal's moon is about 500,000 KMs from the big red planet, which is probably a gas giant. That's about 1/4 farther than the our own moon is from us. The other terraformed moon is earth-sized and about 200,000 kms further in. My intuition is that this picture would look about right. And, yes, there'd be massive tidal forces (lots of earthquakes!) but not enough to break up the planets. Just a wild guess.

Did I hear somebody say "moonquakes"? Don't go there. A certain level of nitpicking is intolerable, even by me!

JOSS, WHERE'S MY CHECK???!!!

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Thursday, September 26, 2002 3:37 PM

HAKEN

Likes to mess with stuffs.

Quote:
Originally posted by Zicsoft:
How can you form any judgment about how big these objects are if you don't know how far they are? And vice versa?

Oh, come on, stretching it a bit here. Granted, there's truth in what you're saying, but the image just doesn't make sense. And you don't need fancy math to know that. A bit of geometry and some basic understanding of gravitational forces and their effects on orbiting bodies will suffice. The orbits are all wrong.

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Thursday, September 26, 2002 3:51 PM

HAKEN

Likes to mess with stuffs.

BTW, let me just add that since Mal and the rest of the folks on that rock he was on seems to be walking normal. Gravity must be equal to that of Earth's (assuming that they still go by Earth's gravity as a point of reference).

So, without needing to know how large the moon he was on is, my guess is that either the planet has very weak gravity or those moons are orbiting the planet really really fast, which, in that case would just cause all sorts of other problems.

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Thursday, September 26, 2002 3:56 PM

LIVINGIMPAIRED

Yeah, yeah, yeah... these are all good points. But we're getting away from the important point: It looks pretty.

________________

"I love to see a young girl go out and grab the world by the lapels. Life’s a bitch. You’ve got to go out and kick ass." —Maya Angelou

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Thursday, September 26, 2002 3:58 PM

HAKEN

Likes to mess with stuffs.

Quote:
Originally posted by LivingImpaired:
Yeah, yeah, yeah... these are all good points. But we're getting away from the important point: It looks pretty.

Yes it does. Never been one too into debating anyway.

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Thursday, September 26, 2002 5:01 PM

MOJOECA

The cool thing about that shot, I don't know if anybody else realized, is that those are the bodies Serenity can be seen crossing over later in the teaser.

--- Joe

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Thursday, September 26, 2002 6:55 PM

JASONZZZ

Overheard Joss telling his writers:
"Okay, let's check the Sci Fi completely
at the door. You have just entered the
world of completely fantasy."

Come on! There has to be *some* element
of believ-ability. I can't just throw
out my entire believe system for the
sake of moronic entertainment. I am
not a big movie-physics buff. But having
that sort of atmosphere, climate,
gravity at that close to that Gas Giant!?

Fantasy I can deal with. Generally
suspension of disbelieve - okay. But I
just can't literally "check my brain at
the door" if I am watching anything
close to a SciFi.

Quote:
Originally posted by LivingImpaired:
Yeah, yeah, yeah... these are all good points. But we're getting away from the important point: It looks pretty.

________________

"I love to see a young girl go out and grab the world by the lapels. Life’s a bitch. You’ve got to go out and kick ass." —Maya Angelou

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Thursday, September 26, 2002 11:48 PM

DELVO

Thinking there's a problem with this is SERIOUSLY off-track from real-world physics and geometry. Where did such an idea even COME from?

For one thing, that gas giant (the big planet) looks almost exactly like a NASA simulation I've seen of how Saturn would look from one of its moons (I don't remember which).

Second, where did this idea of gravity ripping planets apart if they get too close come from? Stars do that, but they have much stronger gravity and are GAS. Planets can have very close orbits and not be damaged; a collision, not an orbit, is where there'd be trouble.

Third, multiple moons of big planets ROUTINELY pass close to each other. So all we're looking at here is a coincidence on the level of a "blue moon" (something that happens once every few months or years).

Fourth, haven't you ever seen the photographs of something with the moon behind it with the moon looking much too large? All you need to do is back off a bit with the camera, and presto, the foreground objects shrink in your viewfield and the distant ones like moons don't.

Also, the moon is currently drifting away from the Earth at a rate that puts it less than half as far away a few billion years ago. So it would have taken up four times as much of the sky. And the only nasty horrible consequence was that there'd be a bit more vertical difference between high tide and low tide. Closer yet would have been possible; there's no reason to think not.

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Friday, September 27, 2002 6:31 AM

ZICSOFT

Quote:
Originally posted by LivingImpaired:
Yeah, yeah, yeah... these are all good points. But we're getting away from the important point: It looks pretty.

Which is always a priority with Mister Whedon. And is actually the main thing I like about the show, despite all my nitpicking. (Hacken, sorry if I got too lectury.) Still, I think that Whedon is trying to give Firefly a semi-solid scientific basis. Those of you who don't care about that stuff can just ignore it. But some of us enjoy SF specifically for that kind of detail, and enjoy arguing about it.

JOSS, WHERE'S MY CHECK???!!!

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Friday, September 27, 2002 7:19 AM

JASONZZZ

I think the problem with the scenario is that there is a bluesky and people walking around on there without the aid of environmental protection. I wouldn't have a problem the whole deal if the environment is violently chaotic and people are basically sealed in barametric chambers. I can deal with fantasy, but just a tiny bit of realism would do.

Quote:
Originally posted by Delvo:
Thinking there's a problem with this is SERIOUSLY off-track from real-world physics and geometry. Where did such an idea even COME from?

For one thing, that gas giant (the big planet) looks almost exactly like a NASA simulation I've seen of how Saturn would look from one of its moons (I don't remember which).

Second, where did this idea of gravity ripping planets apart if they get too close come from? Stars do that, but they have much stronger gravity and are GAS. Planets can have very close orbits and not be damaged; a collision, not an orbit, is where there'd be trouble.

Third, multiple moons of big planets ROUTINELY pass close to each other. So all we're looking at here is a coincidence on the level of a "blue moon" (something that happens once every few months or years).

Fourth, haven't you ever seen the photographs of something with the moon behind it with the moon looking much too large? All you need to do is back off a bit with the camera, and presto, the foreground objects shrink in your viewfield and the distant ones like moons don't.

Also, the moon is currently drifting away from the Earth at a rate that puts it less than half as far away a few billion years ago. So it would have taken up four times as much of the sky. And the only nasty horrible consequence was that there'd be a bit more vertical difference between high tide and low tide. Closer yet would have been possible; there's no reason to think not.

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Friday, September 27, 2002 9:45 AM

HAKEN

Likes to mess with stuffs.

Quote:
Originally posted by Delvo:
Thinking there's a problem with this is SERIOUSLY off-track from real-world physics and geometry. Where did such an idea even COME from?

I wasn't going to say anything, but, this is high school physics.

http://www.astronomynotes.com/gravappl/s8.htm

And please read up on on the Roche Limit.

http://scienceworld.wolfram.com/physics/RocheLimit.html

But, in the end, like LivingImpaired said, all that matters is that it looked pretty.

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Friday, September 27, 2002 11:03 AM

DELVO

Quote:
And please read up on on the Roche Limit.

OK, you got me for badly imprecise writing. I didn't mean to imply that there's no Roche Limit... just that there's PRACTICALLY not one for planets/moons because the limit would be so close that they practically never get that close without colliding anyway... and that the picture doesn't tell us that the Roche Limit has been violated.

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Friday, September 27, 2002 2:13 PM

ZICSOFT

Quote:
And please read up on on the Roche Limit.

Aha! I had forgotten about that. Nice simple model for planet break-upage. Here's a page with a slightly simpler description, accesible to anybody with a little basic math:

http://curriculum.calstatela.edu/courses/builders/lessons/less/les1/mo
ons/roche.html

The Roche limit of two bodies of the same size and density is 2.43 radiuses. Earth's radius is a little over 6,000 km, so two earth-like bodies start destroying each other when the get within about 15,000 km of each other. (If you're metrically challenged, that about 9300 miles.) The terraformed moon in the picture is obviously not that close -- it'd fill the sky if it was.

Quote:
But, in the end, like LivingImpaired said, all that matters is that it looked pretty.

Math can be pretty too!

JOSS, WHERE'S MY CHECK???!!!

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Friday, September 27, 2002 3:02 PM

LIVINGIMPAIRED

Quote:
Originally posted by Zicsoft:
Math can be pretty too!

Not the way my physics professor teaches it.

________________

"You still don't get it. It's not about right, not about wrong... It's about Power." —Morph-O-Monster, "Lessons"

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Friday, September 27, 2002 7:24 PM

JASONZZZ

Check this out: I remember this from a couple of different SF novels I read. Planet bodies in the same solar orbit but very close to each other's Lagrangian points...

http://burtleburtle.net/bob/physics/kempler.html

Very interesting...
Check out his other weird and stable orbits:

Figure 8 orbits:
http://burtleburtle.net/bob/physics/eight.html

Dyson's Swarms:
http://burtleburtle.net/bob/scifi/dyson.html

Quote:
Originally posted by Haken:
Take a look at this from the 'The Train Job'

I'm guessing the largest one in the background is a planet. The other two are moons. One seems to be terraformed. The one Malcolm is on must be a moon as well because there's just no way for two planets to be that close together.

But how the heck do you explain all these terrestial objects being so close together in distance without gravity ripping everything apart? There's just no way.

A bit overzealous with the cut and paste I think.

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Friday, September 27, 2002 7:47 PM

JASONZZZ

Quote:
Originally posted by Zicsoft:
Quote:
And please read up on on the Roche Limit.
Aha! I had forgotten about that. Nice simple model for planet break-upage. Here's a page with a slightly simpler description, accesible to anybody with a little basic math:

http://curriculum.calstatela.edu/courses/builders/lessons/less/les1/mo
ons/roche.html

Actually, we are talking about being just close enough to pass thru the (tremendously strong)magnet field of the gas giant and just enough gravitational influence to rip away the atmostphere and create 100 metre tidal waves - the same gravitational influence would create havoc with the moon's crust. Certainly enough stress to not just create tidal waves with fluids, but with the crust itself. In any case, still not close enough to actually rip the moon apart. Check out a similar comparison between Jupiter and Io. Io and Jupiter's Roche limit is 60223km, but its actual orbit is around 422000km. It has exactly the type of conditions that I described above. and no blue sky.

Quote:
Originally posted by Zicsoft:

The Roche limit of two bodies of the same size and density is 2.43 radiuses. Earth's radius is a little over 6,000 km, so two earth-like bodies start destroying each other when the get within about 15,000 km of each other. (If you're metrically challenged, that about 9300 miles.) The terraformed moon in the picture is obviously not that close -- it'd fill the sky if it was.

slight correction needed there. That result of 15447km is described from center of mass to center of mass. Earth has a radius of ~6350+km. So those two Earth like objects will actually be within staring distance of 2300km from each other surface to surface. With the top of the thermosphere at about 122km. We are talking about really maybe 2000km of separation.

In comparison, driving from Buffalo, NY to San Francisco would cover about 4300km.

Quote:
Originally posted by Zicsoft:

Quote:
But, in the end, like LivingImpaired said, all that matters is that it looked pretty.
Math can be pretty too!

JOSS, WHERE'S MY CHECK???!!!

In either case, you can be about 10x further away and still feel the influence described in my earlier case above. It's likely that all life and life sustaining type environment would get boiled and ripped away wayway before the planetary object actually catastrophically breaks apart.

I don't disagree, it is pretty and thought provoking.

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