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Physics, Astronomy & Cosmology / Re: Could a planet be orbited by another planet instead of a moon?

« on: 03/12/2013 10:38:09 »

Jupiter would be a bright point in the sky, easily visible before sunrise or after sunset (depending on whether Earth was at L4 or L5).

However, if you placed the Earth at the orbit of Io, Jupiter would be a giant sky-filling orb (I calculate that Jupiter would be 19 degrees across as seen from Io, hundreds of times bigger than the Moon as seen from Earth). If Earth were tidally locked to Jupiter, the day would be a rather tiring 42 hours - but with a natural siesta every noon.

Thank you, Kind of what I wanted to hear
I am interested in that Earth being Giants moon idea. Often there are imagined Earth like planets as being moon of some Gas Giant. To have night/day cycle on both sides of that moon it has to orbit the way that it does not get behind Giant at any time or the whole planet would be in complete darkness for some time and one part would never see the sun. I was trying to find out 3d image of Ios path around Jupiter but did not found. It has to orbit in very special way kind of like our moon that it can take sun on both sides during the cycle of day. Or how that work in order to have day and night on both sides?

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Physics, Astronomy & Cosmology / Re: Could a planet be orbited by another planet instead of a moon?

« on: 03/12/2013 01:32:20 »

You see the L4 & L5 describe essentially a loop path, which is also why they are relatively stable.  There may be a single point in the middle that wouldn't move, but many objects move somewhat.

Oh I see now.. thank you.. and so the sizes of those bodies matter? I read somewhere that it may be unstable if the one body is too large as I was giving the example of Jupiter size planet and Earth planet. You think that it could work in with Earth like planet and Jupiter size planet or is there any size balance maximum of those two bodies on the same orbit to be stable? thank you

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Physics, Astronomy & Cosmology / Re: Could a planet be orbited by another planet instead of a moon?

« on: 03/12/2013 00:42:52 »

Jupiter, of course, has Trojans and Greeks.  So, putting a large planet such as Earth into L4 or L5 would likely open the planet up for numerous asteroid collisions.  However, it is quite possible that a Trojan or Greek planet would mop up many of the other smaller asteroids, so by this time in evolution, most of the old asteroids would be gone. 

The planet would likely not occupy a single point in L3/L4, so it would likely follow an orbital path that takes it closer and farther from the host planet.   Distances would still be quite long, but perhaps there would be significant tides on the closest approach to the large planet, and very small tides when farthest from the planet.

Yeah I meant like just the size of that host planet would be as Jupiter not that it would have also the Greeks and Trojans. It would be clear of that, just instead of Trojans and Greeks there would be Earth in L4. So it would not stay L4? It would shift on that orbit of that Jupiter size planet? That is confusing..  I thought that object in L4 the Earth like planet with moon would just follow the orbit of that Jupiter size planet constantly in L4 position, if the orbit is perfectly circular.

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Physics, Astronomy & Cosmology / Re: Large planet instead of moon?

« on: 02/12/2013 23:59:21 »

The one you describe with Earth between Sun and large planet is called L1. Unfortunately, the L1 point is unstable, and any small disturbance (like other planets in the system) will cause it to move out of this orbit. The L4 and L5 points are a better location, as they are stable against moderate disturbances.

Interesting, I was reading that wikipedia article.. But still I have question. What if that Earth like planet with moon (just same as Earth with same environment, people etc..) would be on the same orbit with Huge planet (size like Jupiter or so) and it would be located in L4 position to this huge planet. Would that anyhow affect that human like planet? Or it would be only nice view at some point of the day for the beings on Earth? Thank you

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Physics, Astronomy & Cosmology / Is a stable axial tilt of a planet possible without a moon?

« on: 02/12/2013 14:16:57 »

I am interested if stable axial tilt of planet is aways caused by moons or it may happen without moon. Like that the planet has stable Axial tilt because it had a good kick at start or something like that.  I know our planet would be more unstable without moon and other stable planets mostly have some moons too. So is stable Axial tilt always caused by moons or it may be stabilized some other way, lets say some other objects may stabilize it or it just happened to be stabilized since ever.. or maybe it during the very long time of existing somehow stabilized it self? Thank you

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Physics, Astronomy & Cosmology / Could a planet be orbited by another planet instead of a moon?

« on: 02/12/2013 14:06:43 »

Would it be possible for Earth like planet to have Larger planet instead of moon? As we know moon is important for life on the Earth but I try to find way how to compensate moon by something else. The scenario would be like this:
 There would be no moon. There would be Large planet behind the Earth so the Earth would be between that Large planet and between Sun. This Large planet would orbit in the same way as Earth so they would always be in straight line (Sun-Earth-Large planet). Sun would have gravity pull on the Earth from one side and Larger planet would have gravity pull from the other side. That way there would be tide exchange as it is with moon. and the pull of sun and Large planet would stabilize Earth axis so it would not go crazy. The Larger planet would be placed in proper distance from earth to not consume it but just pull it in the right way.
 Is that concept theoretically possible? Or how could you modify it to make it possible. In way that the planet could hold similar environment as Earth does today.
And would it be possible for life to exist if Earth would have 0 axial tilt as Mercury (but spinning), or it would have 90 axial tilt as Uranus (but spinning towards the sun so the planet would change day and night), or it would have 45 degree axis tilt? thank you

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Plant Sciences, Zoology & Evolution / biological forms with non-organic growth

« on: 12/11/2013 13:09:01 »

Are there any animals or so, who has growth of non-organic matter? For example animal that would live in rocky area and would have actual stones on its skin because of cover-up to not be eaten by predators? Or animal that would live on a tree and would have actual tree bark on its skin because of cover-up?
Or is it possible only to achieve that actual animal has skin made of for example shell and that shell looks exactly as stone by color and texture but it is not stone its shell?

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Physics, Astronomy & Cosmology / Could humans exist in a different solar system environment?

« on: 12/11/2013 12:40:07 »

I am interested if human could live (not with modern technology), in different planetary environment, for example planet with two moons or closer/further from the earth. Lets assume that humans were able to somehow got in to that environment or they evolved somehow the way they are in different environment. I am asking how much that environment could be different from the one we have and what would surely not lead to human evolution. I mean, some environmental changes would surely change the environment that much that human could not ever evolve there, but there must be some environmental changes we could still stand.
Would our environment become human friendly if there would be no moon, multiple moons, or we would be closer, further from the sun (not too much)?
Our planet would be smaller or larger?
What effect has existence of other planets in our solar system on our planet? Would be our planet different if it would be the only planet in the solar system? or some different number of planets then we have now?
Would be life possible if some neighbouring planets were much closer to our planet?
Would be human life possible if there would be different size of sun (assume that our planet would be closer/if smaller and further/if larger)?
And what about multiple suns? Could planet with human life take multiple suns in some proper distance and placement?

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Physics, Astronomy & Cosmology / Is there any program to see universe from different points in the universe?

« on: 12/11/2013 12:14:53 »

I am interested if there is any program or way how to see universe, stars our galaxy, from different point of view then just earth. Lets say some other distant planet of some distant solar system in our galaxy (in the borders of what we have discovered).