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Planetary Orbits
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by
 
on 2006-06-15 10:31:26 |
As far as I know, planets and such revolve around a star in an ellipse, but why is it an ellipse and not a perfect circle or something? 
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Re: Planetary Orbits
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by
on 2006-06-15 12:10:45 (edited 2006-06-15 12:11:03)
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Answer: The Universe is not perfect. You see, the orbit of an object in space depends on the initial momentum and the distance between the orbiting object and the orbited object. Also, the orbital shape depends on other objects in the system. Since we earth-creatures do not live in zero-gravity, such phenomenaare not plainly intuitive. However, play around with a gravity simulator for a while, and you start to get some intuition about such phenomena. http://www.orbitsimulator.com/gravity/articles/simu.html 
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Re: Planetary Orbits
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by
on 2006-06-15 13:20:56 |
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Ok, but look at this (bad) diagram and the following explaination and tell me about it. http://i31.photobucket.com/albums/c384/nickmasterinu/Space-1.jpg I always thought that the reason the orbit is an ellipse is because the planet goes around the star and is "pulled in"(1), accelerating it and giving it the power to "slingshot" out away from the star (2). When it loses enough momentoum though, it is "pulled in" again on the other side (3) and the pattern repeats (with no other variables added to disrupt the cycle majorly).
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Re: Planetary Orbits
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by
on 2006-06-15 14:02:21 |
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Well, that is one way to think of it. You can look at the problem in terms of energy. When the planet is far away from the star, it has more potential energy (farther to fall) and less kinetic energy (speed). When the planet is close to the star, it has less potential energy (less distance to fall) and more kinetic energy (slingshot acceleration).
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Re: Planetary Orbits
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by
on 2006-06-15 15:27:25 (edited 2006-06-15 15:28:02)
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Ok. Mainly what I wanted was to see if my idea of ellipses was right (in a sence). Thx
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Re: Planetary Orbits
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by
on 2006-08-05 11:02:40 |
| That's because of the planet's inertia and the other body's gravitational force. |
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Re: Planetary Orbits
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| A simple way to view why this happen is to imagine a big fabric, add some mass in the center it will make the fabric distort and streach because of its weight, now make a small ball move in a tangent way to the first mass, it will follow a elliptic path due to convertion of kinetic energy into potential and vice versa. In this manner the space is also distorted by mass, producing what we call gravity. |
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Re: Planetary Orbits
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by
on 2006-08-06 20:34:26 |
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totally, space-time is like spandex :D
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Re: Planetary Orbits
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The great funny thing that I've never truly understood, is why the planets have a nearly circular movement... It's almost a perfect circle, except for Pluto, I guess. It has to be an ellipse, of course, so why isn't it an ellipse? I mean, a REAL ellipse, not some crappy elipse with 0.016 eccentricity (Earth) or 0.093 (Mars) or 0.006 (Venus). (the anthropic principle states that if it weren't such a neat circle, we wouldn't be around to watch it... but I hate the anthropic principle) (just checked wikipedia a bit more... Pluto's eccentricity is 0.248, not as much as I thought...)
"From East Middle School, Suzumiya Haruhi.
I'm have no interest in ordinary humans. If there are any aliens, time travelers, sliders or espers here, then come join me."
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Re: Planetary Orbits
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They are almost always neat circles because they would not have survived this long otherwise. The trajectory of the planets, as stated before by Gendou, depends on the initial momentum vs the gravitational pull of the masses affecting it. For example. Earth rotates around the sun. We can calculate the gravitational pull of the sun with the equation G(mS x mE)/r^2 where G is the Universal gravitational constant (6.67 x 10^-11) and r is the distance between their centres. mS and mE refer to the masses of the sun and the earth respectively. Given that the average radius of the earth is around 6380 km and mass of the earth is approx. 5.983 x 10^24 kg, the mass of the sun is 1.988 435×10^30 kg, The average distance between the sun and the earth is 1.496 x 10^9 km, and the sun's radius is 6.96 x 10^5 km, We can find the force of gravity that affects the earth from the sun.  |