How did scientists proved that the planets' orbit are elliptical.?
104516
By carefully and meticulously studying their orbits and taking note of their positions in the sky night after night for many many years. This work begun with the invention of the telescope but it wasn´t until Johannes Kepler got his hand on all that work, including the work of his mentor Tycho Brahe, that the elliptical nature of planetary motion was discovered. Until then planets were thought to be moving in perfect circles for many resons except scientific. The circle was a nice and harmonic shape. But Kepler, with all those measurments at his hands, couldn´t fit the circle into his charts and models. He thought for years about what other geometrical shapes could fit it and eventually thought to try the ellips. And it fit in (almost) perfectly. From that breakthrough he was able to come up with simple mathematical explanations for planetary motion, now dubbed Kepler´s laws. Isaac Newton later expanded on those laws and the result were Newtons laws. Kepler published his work in 1609 in a book called New Astronomy. (Some errors in Keplers laws could not be explained and corrected until Albert Einstein introduced his work on the space/time relation.)
224099
It's not that strange, why would you expect the Earth's orbit to be a perfect circle.\n\nEverything revolve in a elliptical orbit, because they can't all start moving in perfect circles, that's impossible, so when Earth got closer to the Sun, it basically falls and accelerates because of gravity, but because it's now faster, it can bypass the Sun so it won't crash into it.
1068958
Astronomers define a coordinate system on the sky that lets them identify the relative positions of stars, planets, the Sun and other celestial phenomena (the coordinates are called "right ascension" and "declination", but we don't need to worry about that here). Because of their great distance from the Earth, the positions of most stars are fixed on the grid. The positions of the planets and the Sun, however, are seen to "travel" through the coordinate grid in systematic (though sometimes complicated) patterns. The paths of the planets was carefully observed by Tycho Brahe in the late 1500s. Following Brahe's death in 1601, Johannes Kepler used the data to develop a set of laws that govern the way the planets move around the Sun (he proposed them in 1609). These laws, (creatively) called Kepler's Laws, still hold today.\n\nWith Kepler's laws in hand, one can easily interpret the motion of the Sun through the coordinate grid described above as the result of the tilt of the Earth by 23.5 degrees with respect to the plane in which the Earth orbits the Sun. Since Kepler was the one to correctly interpret the motion of the planets and the Sun through the sky, he is the one that I would attribute the title "Discoverer of the 23.5 degree tilt", in the early 1600s.
338602
There are a number of observations that prove Earth moves around the Sun. Astronomers have found that relatively nearby stars appear to move horizontally back and forth slightly over a year's time. This effect is due to a phenomenon called parallax which in turn results from Earth's movement around the Sun. Also Earth's measured movement through the cosmic microwave background radiation is consistent with our orbit around the Sun.\n\nThis website has a more complete discussion about proofs of Earth's orbit around the Sun --\n\nhttp://curious.astro.cornell.edu/question.php?number=190
64442
Planets are round because they have enough gravity to cut down elliptical or uneven parts in a sphere.
52806
Pluto's elliptical orbit is unusual. It is the only planetary orbit which crosses that of another planet (Neptune), and it is tilted 17 degress with respect to the plane of the solar system.
1090100
This can be answered very, very simply.\n\nRelativity works well in  in it's area of expertise, astronomy and space science.  Basically, the scientists took the answers (how the planets revolve around the Sun, the Mass of the planets and stars, how the stars and galaxies move) and created an elegant series of equations to explain them all.  They believed their equations to be correct because this is what they were observing, so it must be true right?\n\nWell no, as we built better telescopes we began witnessing objects and entire galaxies moving far too fast for their observed mass, defying the equations and defying gravity!  It wasn't light pressure robbing these celestial objects of a few arc seconds, which is what sprung Einstein to whop up Relativity.  Venus was so much of a mystery, but Einstein cracked it, right?\n\nWRONG!  If the atom doesn't fit, you must aquit!  Electromagnetic forces have been known to cause these very same effects we witness the galaxies doing.  If the astronomers can't explain something they see, they blame it on magnetics.  Double-helix galaxies, just like our DNA, are floating around out there.  That should tell you where you should start looking to explain the molecular and Universal connection.\n\nVenus' orbit is nearly a perfect circle, and it spins the other direction very slowly.  It used to be called the hairy planet, the smoky planet, and bearded planet.  It's latin name means morning star.  It was literally glowing!  I'm sure some electromagnetic stuff was going on with it, and that would help explain it's brand spanking new surface.\n\nhttp://answers.yahoo.com/question/index;_ylt=AuzSsKSIJO_WapqWQB7tQcPsy6IX?qid=20060612222952AAFdmeo\n\nMars got blown the hell up.  That's a start on finding out about it right there, google should take you the rest of the way.  Hope this helped you understand why those two theories will never be united.  One of them, relativity, was based on a few wrong assumptions.
686826
What is earth co-ordination ?\n\nThe ellipsoid effect manifest itself in the form that things weigh more at the poles and objects as they near the equator orbit at higher speeds than those farther away.
29403
The planets were formed by the same cloud of swirling rocks and dust, so when they came together and formed the planets they were all going the same direction. And actually, since the sun was made from the same stuff, it actually rotates in the same direction, though it is hard to tell because there are no surface details to see from earth without assistance to see the movement of the sun. I think astronomers see the rotation of the sun by watching sun spots. \n\nAnd actually they do not all lie in a flat plane. There is actually a small difference between the orbital planes of each of the planets.
469675
Planets came from clouds of spinning gases that later solidified.   So they are pretty round, but not exactly spherical.  The earth is around 8,000 miles in diameter.  Black holes are proven.  They were proven using gravity experiments on nearby bodies and light experiments from stars "behind" them when viewed from earth.
143927
the second proposition is a formulation of Euclid's postulate of the paralleles.\nIt's precisely a postulate, as the same Euclid posed it; rinascimental mathematicians tried to prove it as a theorem, but they failed: in fact Euclid knew well what he was doing.\nThe postulate of the paralleles defines the Euclidean geometry, which is "platonic": it needs abstraction, because you can't apply it on the spherical surface of the Earth.\n\nSo the answer to your first question is no: if you assume spherical geometry, and thus parallels as maximum circles on the sphere, the angles postulate doesn't work anymore.\n\n(Notice that ancient Greeks were able to measure the Earth's radius by astronomycal calculations: so they knew very well how the Earth was not planar ... )
168060
Circular. Imagine that you have a weight on a string, and you whirl it around over your head. That's the basic gist of it. However, in real life, orbits are elliptical.
266432
This is tricky without a particular formula to derive. The master of this was Richard Feynmann. Try his Six Easy Pieces. His lectures on the motion of the planets and his autobiographies are fun easy reading.\n"Surely You're Joking Mr Feynmann"  is the first.\nThe Physics Lecture series are classic physics books.
985857
GREAT QUESTION!\n\nThe answer is: In several ways.  First of all:\n\n1. Earth rocks!\n\nInstead of following a smooth Keplerian orbit around the Sun, Earth's own centroid performs an oscillatory motion about this "mean path."  By careful observations of the nearest PLANETS (but not the Moon --- why not?!) the amplitude of this Moon-induced "rocking" can be measured: Earth's centroid wobbles back and forth by about 3/4 of the Earth's own radius.  From this alone, one can deduce that the Moon's mass is ~ 1/80th that of the Earth.  \n\n[How?: From cunning arguments, the Greeks worked out long ago that the Moon was about 60 Earth radii distant; but when things are orbiting around one another with an equal but opposite force attracting them, it's the centroid of the COMBINED system that stays fixed, and the sizes of the "orbits" of both objects about their common centroid are inversely proportional to their masses --- just as though there's a giant Archimedes lever out there in space!  So that's how the "60" and the "3/4" combine to tell you that M_moon ~ M_earth/80.]  \n\nFurthermore, THAT is how it was already known in Victorian times that the gravitational acceleration at the Moon's surface must be ~1/6th that of our familiar 'g' at the Earth's surface.  \n\n[The ACTUAL PHYSICAL distance to the Moon is also needed to work this out, so that one can obtain its physical from its angular size.  You then plug the Moon's mass and physical size into Newton's Law of Gravity, applied at the Moon's surface.  Since the Greeks knew the Moon was ~60 Earth radii away, that actually meant measuring the Earth's size well!  \n\nWhen Newton made his own first "Moon check" on his law of gravity, it didn't seem to fit.  He was away home from Cambridge, in Lincolnshire, avoiding the Great Plague of 1666, and thus away from up-to-date books and other information.  But some time later, perhaps on returning to Cambridge, he learned of a new measurement of the Earth's size.  He then went back to his Moon test again, and found that when he'd corrected his earlier calculation, "it answered pretty nearly."  \n\nThat's how he first confirmed his Law of Gravity.  It tells you something about perseverance.]\n\nSo in the end, things like the acceleration at the Moon's surface were already known long before an astronaut demonstrated the "strength" of it by dropping objects on the surface of the Moon, on live television. \n\n2. The tides.\n\nAnother effect of the Moon's gravity on the Earth is of course the tides, though this is a more subtle and less direct (scientific) effect, as it's then the DIFFERENTIAL TIDAL FORCES (derived --- chuckle --- from differentiating the Moon's gravitational force at different places all over the Earth/Oceans etc.) that provide the forcing effect.  However, as we are riding on the surface of the Earth itself, we can ourselves more directly experience and observe this more subtle effect, through the tides, than we can the "rocking" produced by the stronger, main part of the attraction.\n\nI hope you get to study this some day; it's fascinating stuff!\n\n[Here's a funny thing that has always intrigued students at Starfleet Academy.  As viewed in a frame of reference in which the Sun is at rest --- the frame you use when you want to show the planets orbiting the Sun --- what do you think the path of the Moon looks like in space?  Does it spiral a lot, in overlapping circuits, around the Earth's path, or does it slowly and majestically make a gradually curving sinusoidal like motion, first curving in, then curving out (relative to the solar direction) about the essentially circular path of the Earth?  Would you believe that it always CURVES IN TOWARDS THE SUN?!!\n\nIf you know about gravity, acceleration, and the two separate orbital velocites
347854
It's pretty arbitrary isn't it? Look down on the North pole and the earth is turning clockwise, look down on the South Pole and it's the other way around.\n\nA more interesting question is: why are (almost) all planets orbiting and rotating in the same direction?\n\nThe solar system, earth included, is supposed to have formed from a dust cloud that contracted due to gravity. This cloud rotated in a certain way. As spin has to be conserved, all bodies in the solar system rotate in the same way.
111203
I think the current theory is that it comes from the origin of the solar system as a spinning mass of material. This material had a certain angular momentum, which was retained as the material coalesced into the sun and the planets and moons and other bodies. So there are only a few planets and moons whose orbital and rotational angular momentum vectors are not aligned with each other (like Neptune, and Venus, Triton and a few of the smaller, more distant moons of Jupiter and Saturn).
182867
The basic observations were done thousands of years ago. THe ancient Greeks knew that the direction of the pole changes over time (also known as the progression of the equinoxes). Of course, it wasn't until recently that this effect was explained by the wobble of the earths axis. It used to be seen as just another cosmic cycle.