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gravity an attractive force?


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Earth is indeed attracted to the sun, it`s just that it`s velocity of travel at 90 degrees to this gravitational force keeps us in a safe orbit.

it`s a nice balance between going in a straight line across the sun and going in a straight line directly into the sun.

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The earth is attracted to the sun. If there were no attraction between the earth and the sun, then the earth would not stay in orbit. Imagine a ball on a string. If you swing the ball around in the air, it goes (more or less) in a circle. The string represents gravity, and you would represent the sun. Should there be no gravitational attraction (say, we cut the string), the ball (earth) flies off in a straight line.

 

Laugh out loud at the coincidences of life:-p

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my explanation isn`t great but I think a more scientific wording would be along the long the lines of having 2 lots of linear momentum at 90 degrees to each other making a uniform angular momentum, or something like that :D

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according to newton gravity is an attractive force.in that case earth should be attracted towards sun isn't?

 

This maybe silly but a small doubt

 

Yes, the earth is attracted toward the sun and is constantly accelerating toward it. The ball on a string is a good analogy. The earth doesn't fall into the sun because it is moving sideways, so that the direction it is getting pulled is constantly changing.

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There would be serious questions to be asked if it was proven that all planets are getting further away from the sun, ie, what was the planet's past (where did it come from)?

 

Just sayin'

Edited by traveler
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The earth is quite literally continually missing the sun.... (as the others have said, this is due to it's tangential motion)

As Arthur Dent (from Hitch-hikers Guide to the Galaxy) found out. The way to fly is to throw yourself at the ground and miss. ;):D

 

The Earth has "thrown" itself at the Sun, but it keeps missing because it is also moving sideways. :D

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This is a tad off-topic, but I have a question relating to the gravity of the sun and Earth. If the sun or Earth were to gain a lot of weight (suppose the Sun got hit by a bunch of meteors or something and got heavier), do you guys think that the gravity would increase enough for the Earth to be pulled into the Sun?

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No, but the earth would be pulled closer to the sun. It would still be an orbit though.

The way this would happen is that as the Earth "Fell" towards the Sun, it would accelerate (get faster), and if something is in a lower orbit it needs to orbit faster. Eventually an equilibrium would be reached and it would settle into a stable orbit.

 

However, this orbit would not be circular. The way the planet would settle into a stable orbit would lead it to become more eccentric (elliptical). This is because a faster moving object will move away form the Sun.

 

So on one hand the increased mass will cause the Earth to be pulled closer and this will cause it to accelerate and avoid being pulled further in. On the other hand, this increased velocity will cause the Earth to move away form the sun, which would slow it down and cause it to move inwards again.

 

As this would occur in different parts of the orbit, the Earth would enter into a more Elliptical/Eccentric orbit.

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Earth is already in a slightly elliptical orbit, being closest to the sun in the Winter and farthest in the Summer. Of course, we still have our seasons the way they are here in the northern hemisphere due to the sun's angle at which its rays strike the earth.

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closest to the sun in the Winter and farthest in the Summer. Of course, we still have our seasons the way they are here in the northern hemisphere due to the sun's angle at which its rays strike the earth.

IIRC it is closer to the sun in the Southern Hemisphere's Sumner, and further away in the Northern Hemisphere's Sumner (southern hemisphere's winter).

 

Earth is already in a slightly elliptical orbit,

Yes, that is why I said a more eccentric/elliptical orbit.

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IIRC it is closer to the sun in the Southern Hemisphere's Sumner, and further away in the Northern Hemisphere's Sumner (southern hemisphere's winter).

 

I don't think so. Distance from the sun has no effect on the seasons, so I wouldn't expect them to be correlated.

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Earth is already in a slightly elliptical orbit, being closest to the sun in the Winter and farthest in the Summer. Of course, we still have our seasons the way they are here in the northern hemisphere due to the sun's angle at which its rays strike the earth.
IIRC it is closer to the sun in the Southern Hemisphere's Sumner, and further away in the Northern Hemisphere's Sumner (southern hemisphere's winter).

Perihelion currently occurs in early January. dirtyamerica is correct -- now. We'll have to wait ten thousand years or so for Edtharan to be correct.

 

Distance from the sun has no effect on the seasons, so I wouldn't expect them to be correlated.

Distance plays a minor role. The Earth's eccentricity helps make seasonal variations a bit less extreme in the northern hemisphere than in the southern hemisphere.

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I thought he was commenting on dirtyamerica's statement that "Earth is already in a slightly elliptical orbit, being closest to the sun in the Winter and farthest in the Summer" and saying that the minimum of the elliptic orbit was during the southern hemisphere's summer.

 

I am not saying this is wrong. I genuinely don't know, but if it were true, then there should be some mechanism to explain why it would be true, and I would like to know what that is (although I suppose it could just be coincidence).

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I don't think so. Distance from the sun has no effect on the seasons, so I wouldn't expect them to be correlated.

I know that the distance it moves is not enough to effect the seasons (otherwise why would we get Summer in one hemisphere and Winter in the other), but the Earth's orbit is not perfectly circular, it is slightly elliptical it also means that at one point it will be closer to the sun than at the opposite side of the orbit. From what I remember of Astronomy classes, it is when the angle of the Earth due to its tilt (rather than the orbit) exposes one hemisphere to more sunlight than the other, and currently when the Southern Hemisphere is in this position that the Whole Earth is slightly closer to the Sun due to its slightly elliptical orbit.

 

Over time this does change and the Northern Hemisphere was once closer (and will be again).

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I think This: http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Seasons.shtml clears it up nicely.

 

the 1`st sentence says it all really; "The Earth's seasons are not caused by the differences in the distance from the Sun throughout the year (these differences are extremely small). The seasons are the result of the tilt of the Earth's axis. "

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The next perihelion passage will occur on January 4, 2009: dirtyamerica was correct. This is not a fixed date. It exhibits short and long term variations.

 

In the short term, there's a phase of the moon effect on the time of perihelion passage. (Perihelion passage will be on January 5 in 2012 (full moon January 8, 2012), but on January 2 in 2013 (new moon January 12, 2013).

 

In the long term, the perihelion passage varies because of the precession of the equinoxes and the anomalistic precession. The precession of the equinoxes makes the tropical year (our calendar) about 1223.78 seconds shorter than the sidereal year. The anomalistic precession makes the anomalistic year about 282.77 seconds longer than the sidereal year. Time of perihelion passage advances by about 1 day every 57 years.

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