what causes mars to seem to move backwards in its orbit?
347602
It's called 'retrograde' and it is has to do with how the orbits of Earth and Mars differ. Here's a good source for you, \nhttp://www.astro.uiuc.edu/projects/data/Retrograde/\nhttp://mars.jpl.nasa.gov/allabout/nightsky/nightsky04.html
759329
There are 2 ways to think abut it.\n\nOne way is that the centrifugal force of the orbital motion balances the gravity of the Sun, so if the Earth is orbiting a little too slow, it falls toward the Sun. But as it falls, it speeds up which increases centrifugal force faster than the decreasing distance can increase the pull of gravity. The result is that the Earth ends up closer to the Sun but going too fast. The extra centrifugal force causes the Earth to fly away from the Sun, but as it does it slows down. And it slows faster than the rate at which gravity gets less with distance. The result is that Earth ends up farther from the Sun and going too slow, just where it started from. This repeats forever to make an elliptical orbit. The only way to get a circular orbit is for the Earth to have exactly the right speed, not even off by a millionth of a mile per hour from the right speed. That would never happen in nature, so all the orbits are more or less elliptical.\n\nThe other, more physically accurate way of looking at it is the Earth is always falling into the Sun, but the "sideways" orbital motion makes it miss the Sun to one side all the time. If it is going too slow, it doesn't quite miss the Sun enough and ends up falling a little closer. But as it falls, it speeds up. And from here on the explanation is the same as above, but it is the sideways motion allowing a continuous fall instead of a balance between gravity and centrifugal force. The reason this is more physically accurate is that centrifugal force isn't real. It is a virtual force, but that is confusing to most people not schooled in physics.
66192
It is due to the slight orbital eccentricity of Earth rotation around the Sun. Since the orbit is not perfectly circular the distance between the two bodies varies.
1125215
because the mass of sun is higher than all the other planets ...Moon has a smaller mass compared to earth so it revolves around the earth ...actually it's all 'relative' ...Motion is relative ...if you are driving in the car ...you can say the whole world is moving backwards ....we don't say that ...beacuse of the frame of reference ...we have chosen i.e. "the driver" also the complexity of the motion ....involved when looking at the world the other way....similarly you can say that sun is revolvin the planets but in the frame of reference the motion would be very complex ....so we choose the easier frame of reference ....alo the whole galaxy is rotating ...if you look from the outside frame of reference ....\n\n\nMOTION HAS A DUALITY ....NEVER A SINGULARITY ....
476884
Venus rotates clockwise (as seen from Earth) in retrogate rotation as well as Uranus and Pluto. However, it is the only terrestrial planet that rotates in the opposite direction. The theory is that a large asteroid impacted it and that reversed its motion. As a result, it orbits the Sun faster than it rotates, creating a hostle environment with hot surface temperature, making it the hottest planet in the solar system, (hotter than Mercury, although it is closer to the Sun).
990192
i got a look at the conjunction on thursday night when mars was passing in front of the beehive star cluster (m44) -- very beautiful in a wide field telescope.  this would have been about half a day after the astronomy picture of the day from the link below was taken.  mars moved a bit to the left from where it is in that picture during that time.
767312
Mars takes 688 Earth days to orbit the Sun once.  This is a bit less than two Earth years (730 days), or not quite 6% less.  So about ten orbits, depending on when in 1987 you want to count from..
130418
There is really only three planets that exhibit retrograde motion; Venus, Uranus and Pluto. \n\nWhen viewed from the vantage point of the north celestial pole, the planets rotate on their axes in a counter clockwise direction, except for Venus, Uranus and Pluto, which rotate in a clockwise (i.e., retrograde) direction. \n \nIt is also interesting that the rotational axis of Uranus is roughly orthogonal to those of the other planets, almost in the plane of its orbit. \n\nInterestingly, all of the orbits of the planets are also in a counter clockwise direction, as the rotation of the sun.
537473
There is something to this.  The net angular momentum of the Earth-Moon system is such that it is fairly stable to the small torques introduced by other planets.  For instance, the orientation of Mars' rotational axis is believed to have changed dramatically over time.  This is shown with numerical models. \n\nThe moon is moving farther away from the earth.  Angular momentum  is transfered by tides.  The tidal bulge of the Earth remains oriented towards the moon.  The earth rotates under this bulge and drags it forward a bit. The gravity of the bulge itself then pulls the moon ahead in its orbit some.  The net effect is the earth's rotation slows, and moon moves to a slightly larger orbit.\n\nAt some point, the Moon's orbital period will be the same length as the Earth's rotational period and the Earth and moon will be tidally locked to one another. \n\nRegardless, the entire system will still have a lot of angular momentum and the Earth will be fairly immune to significant changes to the obliquity of its rotation.
854008
The force is mv^2/r, and with a bit of algebra to convert period into velocity, you can do the math.  The force is, of course, Mars's gravity.
841326
I think you mean the Mercury transit - Mars never passes in front of the Sun from Earth's perspective.\n\nThat said, I don't know.  I bet www.spaceweather.com has info about where you can view it from.
625130
Gravity is only one of the reasons that the planets move in an eliptical path instead of a perfect circle.  As the planets move closer to the Sun they build up speed, which causes what is known as the Sling Shot Effect.  NASA uses the same effect to build enough speed on their space craft to produce the proper lunar tragectory.  As the craft moves around the Earth it builds up speed; when combined with boosters it allows the craft to break the gravitational pull of Earth and shoot out towards the Moon, Mars, etc.  The thing about the planets is that they don't have boosters, and the gravitational pull of the Sun is so strong that it's impossible for them to break their path, but the planets weigh enough that their momentum directs them in an eliptical path, instead of a circular one.
447889
As the Pioneer spacecraft traveled through the outer solar system, their trajectories were altered from the predicted course for unknown reasons.  There are a number of theories as to why this may be ranging from human error to new concepts in physics:\n\n* observational errors, including measurement and computational errors\n* deceleration by gravitational forces from unidentified sources such as the Kuiper belt or dark matter\n* drag from the interplanetary medium, including dust, solar wind and cosmic rays\n* gas leaks, including helium produced by radioactive decay escaping from the spacecrafts' radioisotope thermoelectric generators\n* radiation pressure of sunlight, the spacecraft's radio transmissions, or thermal radiation pressure from the RTGs\n* electromagnetic forces due to an electric charge on the spacecraft\n* clock acceleration between coordinate or Ephemeris time and International Atomic Time.\n* A modification of the law of gravity. The theory known as MOND (MOdified Newtonian Dynamics), states that at low accelerations, the force of gravity deviates from the traditional Newtonian value.\n\n\nResearch is ongoing to attempt to determine the cause of the Pioneer effect.
176123
The force that pulls you towards the side of your car when you go around a corner too fast is actually inertia.  It's the same force that makes you fly forward when you hit the brakes too fast or sink into your seat when you lay on the gas.  According to Newton (I believe it's his third law), "an object in motion tends to stay in motion and an object at rest tends to stay at rest."  Well when you are in your car and you are moving in a straight line, your tendency is to keep moving in that straight line.  When you take the turn too sharply, the car is turning but your body's natural tendency is to keep moving in that straight line, so you get pushed up against the side of the car.  The same justification explains why you move forward or back when the car accelerates or decelerates too quickly.\n\nCoriolis force is a completely different force that is caused by the rotation of a sphere and the fact that the sphere is densest in the middle, with decreasing density as you approach the poles.  This change in density causes a force which makes moving things tend to move towards the equator of the sphere.
515806
The earth rotates on its axis (spins) the same way as the sun does on its axis, since the planets all formed out of the proto-solar disc when the sun was forming.  All of the planets spin the same way, EXCEPT for Venus, which rotates (very slowly, once every 243 days) in the opposite direction.  Some planetary scientists consider this evidence that Venus at one time collided with another large body early in its lifetime, which caused the retrograde rotation.
691441
it is constantly changing since the moon rotates around the earth and the earth rotates around the sun just as mars rotates around the sun. Since the earth is 93 + or - million miles from the sun at any given time the planet mars is farther out from the sun than the earth. So if we are at our most outer distant positions 93 mil *2 and then some... would be our most distant position from each other. If we were at our closest it would be much less than 93 mil... these are estimates, but our distance can be a wide range of points in between 200 million to 45 million miles between the moon and mars. Hope this helps.
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