why are most celestial bodies spherical or oval in shape...?
366583
This is because of their centre of gravity.\n\nAll of their constituent mass is  pulled with an even force into the centre of the object....thus the surface of the celestial body is equidistant from the centre...ie. almost spherical.\n\nMany are in fact oval due to the fact that they spin around. This moves some of the mass to the equator of the object....rightly due to centrifugal force.
47522
In a nutshell, planets are round because they are sufficiently massive to attract all of the material towards the centre.  When a planet forms, it is made of molten rock, that is very much like a liquid.  This liquid rock will try to take the path of least resistence (the shortest path) to the centre.  The only shape that would allow liquid on every spot of the surface the same ammount of effort is a sphere. Today, rocky planets still have molten cores and this shaping process continues.
350009
I believe its oval. It would look like a box if it was square..No?
455949
everything in this universe moves. stars are parts of galaxies. for example our sun is a part of the milky way galaxy. we are in the sagittarius arm of our galaxy which rotates about its centre and as we are in one of the outer arms as the galaxy seems to rotate the sun along with its nine planets revolves around the centre of the galaxy. this is exactly what happens in other stars and star systems. secondly  all stars are round not to mention, every heavenly body is round because gravity makes them round. and the shape we concieve is just because of the phenomenon of scattering of light as the light from the stars passes through various layers of the atmospheres of different densities
967418
yes there are straight lines. what you describe is according to the earth and the solar systems that appear round due to the force that acts from all directions creating a universal container (the sphere) which is round. But look at the BIGGER picture a straight line has to exist even if it is as small as an atom (universe - meter scale). also there are other geometrical forms. infact the only reason why round is soo common in all universal shapes (objects). well think of all forces acting on a body from all sides then reason the kind of shape it will produce when all forces level out the object.
991212
If you follow astronomy like I do they are discovering everyday that the Solar System is not what we thought it was!  Our Universe actually may look round/spiral but if you tip it on its side it is pretty flat.  The answers relating to gravity are sort of right as well, but scientists have found just recently (few weeks) that some of our planets aren't perfectly round like everybody thought.  As we send more cameras into space the more we realize that what we thought was fact...is wrong!  Scientists are saying "oops" quite a lot this past year or two!  But yes, gravity plays a role, but when you look closely, they are not perfectly round and flat.  They have gigantic craters, mountains pointing up so high we can't even imagine it.  Our telescopes are getting more powerful as the computer age expands our capability.to see so much better.  Its a great field of study, especially today and tomorrow.  Things are changing our perspective on what we thought and what we are learning is the truth.  The sun may appear round, but it is gaseous so bellows, in and out, with flares and cool spots, same with the storms on Jupiter, they just recently realized that the Big Red Spot MOVES! Yep, science was shocked to learn that the Red Spot moves all over the planet!  So study and explore, the Digital Science Channel, and Discovery Channel is what every one should be watching, not The Simpsons, although Bart is a lot more funny.  But science is always changing, nothing ever remains the same!  Become an exployer of the Universe, and get paid for having fun in discovering new stuff all the time!
1069514
By Newton's law of graitation any mass is attracted by another mass. Since the planets are matter like our Earth, the pull of gravity in all directrion make the planet spherical.\n\nThe spin of the planets about their axes actually make them close to  ellipsoid of revolution and not spherical. Our earth is also  close to ellipsoid of revolution.
57491
because of gravity, pulling inward with the same force in all directions, giving them a round shape.\n\nyou look very pretty in your avatar by the way ;)
34520
Gravity shapes objects.  If an objects mass is over a certain threshold then gravity will be strong enough to overcome molecular forces to "mold" an object.  Most asteriods have masses that are too low for this however planets and most moons are massive enough.  \n\nWhy a sphere?  This is due to the inverse radial dependance of the gravitational force.  In order words at a given distance from the center of mass distribution the force of gravity is the same.  This type of shape is a sphere.
184588
we know the shape of the solar system because we know from tracking the movement of planets that they orbit the sun, as they orbit the sun they must be going round it, so that is a slightly stretched oval shape. We can estimate where planets are (i.e. how far away they are) by using stars that we know are different distances away and measuring or by using the Hubble Telescope that can see all the way to Pluto and further and measure the distance.
431236
The celestial sphere is not a physical object but a virtual surface (an imaginary sphere, concentric and coaxial with the Earth) used by astronomers for projecting the positions of celestial objects. So, there is no definite radius, it is said to be "gigantic", just as wording convention to mean that it is big enough to contain the projection of whatever far object.\n\nLater addition: the parsec is defined by considering 1 sec parallax of an object seen from two opposite points of the Earth's orbit. So I suppose that in the parsec definition you have read, they used the wording "celestial sphere" meaning a sphere having the sun in the center and the Earth on its border. If this is true, your sphere has a radius of 1 AU (about 150 million km). But note that this is not the mainstream definition of celestial sphere.
231608
If the planets started out in a liquid shape, they would naturally want to try to assume a spherical shape due to their own gravitational forces.  A sphere is the most compact shape, with every point on its surface equidistant from the center, so as the mass settles, it slowly becomes spherical.
228461
Large bodies of matter, like planets, have a strong gravitational field.  The gravity, created by the mass of the object tends to pull the surface into a shape with the least amount of entropy.  This shape is a sphere.
339322
if any object following a straight or whatever path was to be attracted by some other larger body and put into and orbit then thru mathematical equations the orbit will always be elliptical(considering variable decceleration and velocity) that's why there is a doubt that moon was just a passing object that earth caught up..(coz it's orbit is circular and that it perfectly covers up the sun during eclipses....search for anomalies of the moon on google) so the orbit cannot be circular unless u "put" an object specifically into that shaped path...\n\nregards...\npretty rough explaination ..sorry cud not include the equations :)\n\nvivek
422854
The moon although is a sphere, but it is so far away that it appear a flat round disk. there is nothing strange about this and if people are not educated that moon is a spherical rock, they'd probably think it's a round flat disk.\n\nBut for me, I see it as a hole in the ceiling.
477513
When an object rotates, it has centrifugal force that pushes on its sides, flattening the disk. True, Pluto, Santa (2003 El61), Quouar, Sedna, Buffy, and most kuiper belt objects are not in orbit along the plane of the ecliptic (the usual plane of the orbits), their odd orbits are usually blamed on gravitational influence from Neptune, or a passing star. Comets are also usually not in the plane of the ecliptic. As of this date, I believe, there are no objects in orbit 90 degrees to the plane of the ecliptic.\n\nGalaxies are not related to each other (usually, though they can collide). As I understand it, (and I could be wrong), the shrinking of the galactic disk invokes angular momentum, causing the disk to rotate. And much like protostellar disks, flatten out. Stars form in this gas, causing galaxies. Elliptical galaxies have no plane, and are probably what you would describe as 'multiplane'. Their stars orbit anywhere, and everywhere, around the center.
468156
Most--not all--shooting stars (meteors) are about the size of a grain of sand. Most of these specks are left-over material from comets that have passed in and out of the inner solar system.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com