Why do planets move along elliptical paths and not circular orbits?
549175
Planets would only describe circular orbits if they were moving with the correct speed for their distance from the sun. Any slight disturbance to their motion, such as asteroid impact, would cause their motion to become elliptical. For instance if they lost energy (and speed) as a result of a collision they would be pulled closer to the sun as the result of its gravity. This would cause them to speed up and start moving away from the sun until their speed decreased so much that they were pulled towards the sun again. This is the elliptical motion of planets.\nUnless the solar system were intelligently designed it would be impossible (probability = 0) for any planet to be moving in a /perfect/ circle.
1130994
Yes, the planets go through phases. Celestial phases are basically light hitting different hemispheres at different times.
91267
You are referring to a concept in planetary astronomy call inclination of orbit.  The "disc" that the Earth revolves around the Sun on is called the ecliptic plane.\n\nTechnically speaking every other planet has some orbtial inclination or tilt of their disc.  But it is very small so the eight major planets are said to orbit in roughly the same plane (ecliptic).  \n\nPluto is different.  Its orbital inclination angle is about 18 degrees with respect to the ecliptic.  That's big compared to the other planets. \n\nNow the question is why are the eight major planets in the same plane?  Why is Pluto not?\n\nWhen the solar system formed it was originally a giant sphere of gas and dust and over time was gravitationally attracted into a compacted sphere.  When this happens systems need to conserve angular momentum.  This results in the sphere becoming flattened.  This flattened sphere now looks like a disc.  The disc is roughly the ecliptic plane. An analogy to this scenario is pizza dough being spun by a chef into a disc. \n\nPluto, it is believed, was probably originally part of this disc but later had an intereaction with another object which since changed its orbit.
963778
Eliptical orbits. If the orbit were circular, then you'd expect the period to be the same. ...The planet speeds up and slows down and spends more time at the part of the orbit more distant from the sun.
292052
That's a really good question, that doesn't have an answer yet.  The current theory of solar system formation suggests that planets spin in coordination with the orbital spin of the disk of matter that forms the core of the solar system.  The spin of the accretion disk itself is the result of conservation of angular momentum, and can either be clockwise or counter-clockwise, which would be a relatively random process.\n\nThere are 'accidents' however, whereby planets are impacted by other large bodies in random ways and can greatly skew the planetary orbit and/or spin.\n\nSometimes the results are really weird, such as Uranus, which rotates top-to-bottom relative to the plane of our solar system.\n\nFrankly, until we're able to do a survey of planets in our galaxy and a few others, I think it would be hard to guess what the real averages would look like, and whether or not they are random.
425798
Our planet earth and for that matter all planets, moons and stars are generally spheres, not cubes or cylinders or odd shapes. Some small galactic bodies such as asteroids comets do have odd shapes, but planets, suns and stars and even moons look like spheres. That's because, when they were formed millions of years ago, they were essentially molten liquid. Gravity and meniscus forces (surface tension) cause the object to take on a rounded shape--and it cools in that position. Do you remember seeing astronauts squeezing out juice or other liquids, they immediately become round in space.  It is the nature of gravity too pull uniformily toward the center--as the distance from the center increases, so does the gravitational force. You can think of gravity as a force that points inward toward the center of all things that have mass-- so that every part of the surface (especially liquids)is pulled evenly toward the center, resulting in a spherical shape.\n\nPlanets are not perfect spheres because there are other forces acting on the planets too which are trying to stretch them--rotational forces, etc. Because they were once hot moltent liquid, they buldge in the middle for these secondary centrifigal forces. Earth and the moon reflect this phenomina. Although gravity keeps planets close to spherical, there are other forces that cause deviations from the basic spherical shape. For example, the rotation of the earth once every 24 hours, causes an apparent centrifugal force which creates a bulge at the equator. In fact the earth's diameter at the equator is 7,926 miles while the diameter between the poles is only 7,900. \n\nNote that planets and moons had to be a liquid or they would not have been able to escape the gravitational force of the nearest larger body. Remember that liquid will seek the path of least resistance as it moves. In otherwords, an impact on the earth would cause a splash of moltent material that could escape the earth's atmosphere at the exact angle (path of least resistance) to be able to exit the planet's atmosphere without burning up. Once it exits into space, the gravitational pull of the larger body will pull it into orbit. It will stay in orbit until it is acted upon by a larger force. Fortunately, we haven't seen any larger forces since the earth was created and therefore, the conditions will remain for millions of years into the future.
442630
this planet revolves around the sun ,which is a very powerfull all influencing movement.\nall life follows this path.\n\nall spirals in Nature turn anti clockwise.\nthe bean,or vine that winds its way up a tree.\nthe bath water running down the drain,the toilet water going down the bowl,the currants, in the seas and rivers\n\nthe spiral paterns in our bones,the way branches devellop on a tree spiraling up wards in protruding branches.\nwhen you walk in the dessert your path will vere towards this direction \nand is it hard to walk in a straight line,\nmany people right feet are larger than the left,so that you will walk in this curve.\nin construction or actions involving a lot of people,i always make paths ,roadways and trafic go in the anti clock wise direction\nthis results in less congestion or accidents and it is the more natural and comfotable direction for the people .\nputting them in a better mood to work.\n\nthe twister and huricanes and tornados and wheather paterns just follow every body else\nand contrary to myth or ignorence this direction does not change if you go to the other side of the planet,this is an old wive tale.\nif you put a bath tub on the plane and slowly drain it ,the direction does not change all of a sudden when you get to Australia.
731336
Hi. The universal expansion, if it exists, is different from orbital motion. I would guess that all galaxies have SOME non-radial motion, but the overwhelming part seems to be radial.
64442
Planets are round because they have enough gravity to cut down elliptical or uneven parts in a sphere.
384805
The First law of Kepler is: \nPlanets move along elliptical orbits with the Sun\nat a focus.\n\nSo, all i can say is that the sun is relatively stagnant in our immediate universe.\nThe earth rotates along an elliptic orbit around the sun.\nThe moon rotates along an elliptic orbit around the earth.\n\nWell, all "movements" are relative to some reference point.
217587
First I want to clear up that clockwise is really a 2-dimensional description of rotation, and planet rotation can be viewed in 3D so you can't really describe planet rotation as clockwise or counterclockwise. If you define an "up" and a "down" for the solar system, and then say "when viewed from above the solar system rotates counterclockwise", then the "anticlockwise" description works. For my answer we will assume you have done all this and that the solar system rotates counterclockwise, so there is no confusion from the wording of the question.\n\nThe reason the solar system rotates counterclockwise has to do with the way the gas clouds that created the solar system collided. They didn't collide head on. Think of cars travelling in opposite direction down an interstate hitting each other not quite head on (i.e. the left headlights of both cars smack together). When they do this they will spin out sideways - they will effectively rotate around each other (in North America with the cars driving on the right side of the road, they will rotate counterclockwise when viewed from above if they collide like this). The gas clouds did the same thing and their collision exceeded the critical density needed for gravity to take over and start forming the solar system, and as this matter collapsed to form the sun and planets, the rotation sped up. The rotation these gas clouds got from their collision gave momentum to the rotation of most matter in the solar system; the sun rotates in the same direction as those clouds did when they collided and so does most other things, including all the planets.\n\nSo that is why.
859287
I'm certainly no expert, but from my high school physics days I recall something about Bode's law.  You might be able to Google or Wikipedia it.  It was an explanation, in Newtonian physics terms, of why the planets are where they are.
12606
Our world, Earth, is a planet, and planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it. With its large body and internal heating from radioactive elements, a planet behaves like a fluid, and over long periods of time succumbs to the gravitational pull from its center of gravity. The only way to get all the mass as close to planet's center of gravity as possible is to form a sphere. The technical name for this process is "isostatic adjustment."\n\nIf the shape of the Earth were due solely to gravity it would be a perfect sphere (round in 3 dimensions) but it's not, the Earth is shaped like what is called an oblate spheroid. As the Earth spins on it's axis, it produces a centrifugal force that pulls away from the Earth (in opposition to gravity)  at 90 degrees from the spin axis, this corresponds to the equatorial regions. So the Earth bulges out a little around it's middle.
373605
Although all planets' orbits are elliptical, Venus's orbit is the closest to circular, with an eccentricity of less than 1%.\n\nalso...\n\nOrbital characteristics (Epoch J2000) \nSemi-major axis 108,208,926 km\n0.723 331 99 AU \nOrbital circumference 0.680 Tm\n4.545 AU \nEccentricity 0.006 773 23 \nPerihelion 107,476,002 km\n0.718 432 70 AU \nAphelion 108,941,849 km\n0.728 231 28 AU \nOrbital period 224.700 69 d\n(0.615 197 0 a) \nSynodic period 583.92 d \nAvg. orbital speed 35.020 km/s \nMax. orbital speed 35.259 km/s \nMin. orbital speed 34.784 km/s \nInclination 3.394 71°\n(3.86° to Sun's equator) \nLongitude of the\nascending node 76.680 69° \nArgument of the\nperihelion 54.852 29° \nNumber of satellites 0
572633
Aren't the rings about planets just the debris that is spinning around them? If so, then not every planet has a ring because they don't all have space junk that is part of their gravitational field.
712687
If you imagine a solar system that includes the sun and the Earth,and no other bodies, the Earth would travel about the sun in an ellipse (strictly speaking, the Earth and the sun would travel around their common center of gravity in ellipses).  An ellipse has two foci, which are points that define the ellipse in the same way that a point defines the center location of a circle.  Because the sun is so large and the orbit is so nearly circular, both of the foci lie near the center of the sun  So it is not correct to say that one of the foci is the sun -- both foci are in the sun, but they're really just mathematical points that define the shape of the orbit.\n\nWhen you add more planets to the mix, things get much more complicated, but one can think of each approximately elliptical orbit separately, and then there is a different set of foci for each pair of bodies if one neglects the influence of the other bodies.
51021
No. Planets orbit stars.  The earth is a planet orbitting its star, the Sun.